Cathode Ray Tube Experiment-How To Neck A Crt Tube Video

Myads

Cathode Ray Tube Experiment-How To Neck A Crt Tube Video

      

      

Cathode ray tube experiment-If you want to throw a cathode ray tube or crt away, please make sure that you break the crt neck first to let the air go in otherwise if someone accidentally dropped the crt while loading, the crt may implode and scattered the picture tube glass and injured his body. If the neck already broken, the crt tube is just like a normal beer glass. Anyhow, think of safety first even if you want to break the crt neck. If you don't want to break the crt neck, you can always engage a cathode ray tube disposal company that deals with junk computers. Always handle pictube tube with great care!

Monitor Rerpair: Some Common Problems on Monitor

Myads

Infinity Monitor Model: 14ED (W745114477 Chassis)

No power

Checked and tested power supply section, all resistors and filter capacitor checked ok. Replaced IC802 and unit then powered up ok
(Wiland Malapit - Philippines)

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Likom Monitor Model: L503RDN (13MLB0004424 Chassis)
Vertical problem, small picture, cannot adjust, sometimes rolling
Checked vertical section and found resistor R527 (10ohms) located near ICU501 had gone high resistance, replacing resistor cleared the fault
(Wiland Malapit - Philippines)

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Kds Monitor Model: VS21E (Evoked 2100K Chassis)
Dead
I found following parts had failed: Q425, C4924 and R497 (10ohm, 1w), the horizontal output transistor was also short circuit, replaced with type BU2527
(Imran Khan)

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Dell Monitor Model: D-1728D-LS (FCC ID A3LCMG737)
No display
I checked many parts in the Video driver area and found all was ok but IC MM1207 was found to have failed
(Imran Khan)

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Sony Monitor Model: GDM2036S
Monitor dead, green led comes on then fades out, EHT sometimes starts up
Remove power supply (very easy on this monitor). I found C102, C109, C112 and C101 on sub board o/c plus C19, C8 and C9 on main pcb also o/c, all 105deg caps. This is a quality built monitor
(Bernie)

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Mag Monitor Model: DX1795
Reduced width with failure to store settings
Dry joints on the display mode relay RL501
(Lacko)

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Silicon Graphics Monitor Model: 340C (Panasonic PanaSync P70)
No horizontal, single white line up centre of screen
Check fuse link J114 which feeds 220v to collector of Q881
(Steve May)

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Silicon Graphics Monitor Model: 340C (Panasonic PanaSync P70)
Vertical line down centre of screen, no horizontal drive
Check for horizontal drive across C516 (3V p-p both sides) if not change C516 (1uF, 100v), C516 is the blocking cap before the horizontal driver mosFet, also check for bad soldered joints
(Steve May)

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Belinea Monitor Model: 10 70 35 (Panasonic PanaSync P70)
No horizontal, single white line up centre of screen
Check fuse link J114 which feeds 220v to collector of Q881
(Steve May)

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Belinea Monitor Model: 10 70 35 (Panasonic PanaSync P70)
Vertical line down centre of screen, no horizontal drive
Check for horizontal drive across C516 (3V p-p both sides) if not change C516 (1uF, 100v), C516 is the blocking cap before the horizontal driver mosFet, also check for bad soldered joints
(Steve May)

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Iiyama Monitor Model: Vision Master Pro 411 (A705MT Chassis)
Tripping
Change the secondary psu smoothing caps for the 12v, 28v and 80v supplies (2200uF, 25v cap blown apart), the board is also prone to dry joints
(Steve May)

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Tatung Monitor Model: 47/2000 (VT-1980 Chassis)
No video
Change transistor C5521
(Roberto)

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Jean Monitor Model: JD144K (Ver 6.22 Chassis)
No picture, power led blinking, ticking sound
Replaced shorted HOT (BU2508DF). Resoldered dry joints on Q408 & Q412 pins
(Mattiemutare)

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Viewsonic Monitor Model: A75F
Dead
PCB board was cracked across 2 tracers cutting their path. Visible arc burn present. Occurred at position D1. I pulled PCB board out a little to see the crack and soldered the copper tracers to repair them
(Anonymous)

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Dell Monitor Model: EV700B (LA80 Chassis)
White Raster with flyback lines at Power-up, after a while, the green LED starts to blink
Resistor R972 open circuit, results in loss of 103V on CRT Board
(Sharesolution)

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Mag Monitor Model: DJ70E
Dead Set.
Found Resistor R318 (220K) in the power section o/c
(Anonymous)

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Proview Monitor Model: PK-770 (770M)
Reduced width and height with failure to store settings, display otherwise OK, front panel control functioning as normal
Dry joints on the display mode relay (on right-hand side of main PCB, about halfway down). I have had several of these monitors with the same problem
(Ian - Brighton)

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Packard Bell Monitor Model: A720
Board PWB-0172-06 (Hyundai), Green Led flashing - Power supply pumping. No picture
Replace 2SC5386 Q433 on large heatsink near FBT. Transistor has been replaced with BU2525AF
(Yves)

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Packard Bell Monitor Model: 1412SL
Shuts down after 15mins with picture shrinking and dancing
Problem caused by leaky transistor Q212 (C458 npn uni)
(Guruji)

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Packard Bell Monitor Model: 1412SL
Out of focus picture
The problem was the FBT part # TFB-239T
(Guruji)

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Samsung Monitor Model: Syncmaster 750S (DP17LS Chassis)
C508 (2.2uF, 250V) burst
The voltage on C508 appeared around +450V (correct voltage must be +210V), Check C506 (10nF) it was found to be leaky
(Raymundo)

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Lg Monitor Model: FB775C-EA
Dead
Q706 short
(Robin)

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Viewsonic Monitor Model: VCDTS2183-1P (E-40 Chassis)
No power, no LED blinks
Found short circuit HOT and also found bad high volt PF in horizontal area, Replaced with BU2508DF fixed the problem
(Imran Khan)

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Acer Monitor Model: 7276C
No video, no power up
Transistor IRF630 was short
(Anonymous)

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Compaq Monitor Model: MV400
Blown mains fuse
Replace 4 amp fuse and degauss posistor - I have had about twenty similar repairs on this model
(Tony Hamilton)

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Gateway Monitor Model: EV700
Dead
I have found that 9 out of 10 times, the LOPT is dud
(Anonymous)

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Nec Monitor Model: Multisync 75
No HV, goes into shutdown
Have replaced the HOT transistor C5521 which burnt out again. I found the problem was one of the 1600v caps in the yoke circuit that had changed value, Now have to find a .0075, 1600v cap
(Imran Khan)

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Ntc Alpha scan Monitor Model: KM-411 (C-411 Chassis)
Power OK but no display at all
Check for possible o/c fuse / resistor in the high voltage area
(Ian - Philippines)

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Compaq Monitor Model: MV740
Dead with standby led operating normally
R925 (1Mohm, 0.5W) was o/c
(Sami)

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Samtron Monitor Model: 4BNI
No display and power on indication appears a few second and then disappears. SMPS filter capacitor does not discharge at all
Suspect the flyback transformer
(K. Vatcharavelu)

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Dell Monitor Model: D1626HT (SCC-L04KA Chassis)
Cold picture jumps vertically
Vertical deflection IC
(Christopher)

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Hp Monitor Model: Pavilion M70
Display is dark but sometimes comes up to the right brightness, or brightness changes erratically with a relatively slow transition from bright to dark or vice versa
CRT socket has a bad solder joint at the heater pins. Resolder and have a nice day---- anyone know what causes tiny slightly curved HORz ripples at random points on the screen with this model ?
(Offset)

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Compaq Monitor Model: V70
Width can not be increased
Changed all PF (capacitors) near horizontal section
(Anonymous)

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Daewoo Monitor Model: 710BN
Top half of frame scan folded to bright line
Diode D105 was burnt out, this was found to have been caused by capacitor C105 (100uF, 16v) which measured dead short
(Brian)

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Compaq Monitor Model: V45
Very blurry display
This was due to a faulty flyback
(Anonymous)

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Brother / Aoc Monitor Model: Spectrum 7GLR
Dead, no power
There was no voltage at pin 7 of IC901, traced back to R906 ( 1M ohm 1/2W ) which was open circuit, replaced R906 and unit back to normal
(Vitus Luk)

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Compaq Monitor Model: V500
No Power
Replaced D630
(Prasad)

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Iiyama Monitor Model: Vision Master 17 (8617E Chassis)
Horizontal dark line across screen shadowing text or other complex display data - giving appearance of 3D grooves or just dark lines on light background - temp fix (few minutes) by banging monitor or jiggling the video cable (thats what threw me for a while)
Removed tube base board and ran over disc capacitors and other solder joints whether they looked dry or not. No re-occurence in 2 weeks of daily use. Seems to have fixed it. (Be prepared for a lot of metalwork and screw removal when opening one of these up - I still havn't figured out how to get the PSU/main board out of one !)
(John)

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Iiyama Monitor Model: Vision Master 410 (400 Series Chassis)
Set wants to start up, EHT can be heard to screen but then monitor shuts down, all secondary voltage are present for a short time but decay fast
Change all the electrolytic caps in the primary power supply especially the 10uF, 100v electrolytics
(Steve May)

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Malaysia Monitor Model: Titan TE555
No raster
Check C5296
(Anonymous)

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Sun / Sony Monitor Model: GDM20SE20 (N2H Chassis)
Bright raster with flyback lines and reduced width, trips after 5 seconds
Replace the video drive ic on the a pcb located on the rear of the chassis around the crt neck, IC420 type CXA1907S, part no: 875207156. http://groups.yahoo.com/group/TVmonitor_schematic_tips/
(Imran Khan)

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Ctx Monitor Model: PL9
Pincushion problem. Q401 may be shorted. Makes squealing noise
C334 (100uF, 250V) Failed, located at front left side of board just in back of Q311
(Gene)

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Hansol Monitor Model: E14BL (MAZELLAN 401A)
Dark (but visible) display with pronounced ripple, accompanied by buzzing from the chopper transformer. Buzzing also present (but quieter) in standby
C105, the main smoothing electrolytic on the mains input side was completely open circuit. Its value is 220uF, 400V
(Ian - Brighton)

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Sylvania Monitor Model: F96
No green, good blue and red
The crt board had cold solder joints
(Anonymous)

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Ast Monitor Model: VISION 7L
Blows horizontal output transistor intermittently 
L403 (4uH) defective, also check C446 and C451 both 10uF
(Anonymous)

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Iiyama Monitor Model: VISIONMASTER 400 
Powers up but goes dead when video signal applied. If powered with signal attached comes on then trips
Replace ALL the low value electrolytic capacitors in the primary side of the power supply even though they measure OK. Also check the capacitors on the secondaries especially the voltage rail that feeds the feedabck circuit for the power supply
(Arokh)

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Samsung Monitor Model: Syncmaster 753S (ANNN17LS7L/EDC Chassis)
No power
I discovered IC601 (DP704C) had exploded, Equivalent for this IC is 6S0765RC
(Anonymous)

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Philips Monitor Model: 2551
Dead
The BUT11AF was found to be faulty
(Ajesh)

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Philips Monitor Model: 201B10
Loss of horizontal sync at change of resolutions
Change capacitor 2431 (150nF, 63V)
(Anonymous)

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Panasonic Monitor Model: TX-D2151W (ACJ93312118 Chassis)
No power, no LED blink
Replaced the STRS6533 in the power supply
(Imran Khan)

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Pc View Monitor Model: 1512
Dead, fuse ok, led blinking
Mosfet (IRF630A), capacitor (150uF, 400V) and burnt up resistor R720 (9.4k)
(Imer)

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Philips Monitor Model: 105S
Fuse blown, not functioning
Replaced 3.15A AS fuse. Conclusion, fuses suffer from metal fatigue and fail without a serious fault being present. Constant inrush currents of 10A and degauss of similar level at switch on cause this progressive failure mode. Fuse is hard wired
(Mike - UK)

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Hansol Monitor Model: 710A (Also Belinea 103055 Chassis)
Tripping, occasionally works
Dry joint on LOPT, the connection to the line OP transistor. The worst part of this job is getting the beast apart, still the thing only cost £1 from auction and now has a great 17 inch picture!
(Bob Meade, Brandon, Suffolk)

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Siemens Nixdorf Monitor Model: MCM1405
Blew fuse, 2.5A A/S
D901 in bridge rectifer short. Replaced all doides in bridge with 1N4007. No other problems just a faulty diode
(Mike)

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Nokia Monitor Model: 447X
Picture disappears after 10-30 minutes of use, may reappear if monitor tapped
Dry dry solder joints on the video card
(Anonymous)

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Topcon Monitor Model: AM1782 (MT7A73029086 Chassis)
At power up there is a Black screen only
I checked the circuit and found that the PWM IC, KA3842B C826C (8 DIP) had failed, everything else appeared ok
(Caleb)

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Viewsonic Monitor Model: E-40 Digital 14"
Int loss of display
There were dry solder joints around the power output area.http://groups.yahoo.com/group/TVmonitor_schematic_tips/
(Imran)

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Aoc Monitor Model: CM336
Dead with PSU tripping. The chopper transistor and PSU transformer were getting quite hot
D920 (PSU secondary HT rectifier) was s/c. Replacement provided the fix
(Tom Crane)

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Aoc Monitor Model: CM336
Intermittent loud whistling made for a very irritating fault
Varnishing the windings of horizontal linearity choke L804 cured the fault
(Tom Crane)

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Aoc Monitor Model: CM336
Bad horizontal linearity with picture bowed out at the centre but only on the higher res. screen modes
C8105 (0.84uF, 250V) had gone low in value. Replacement provided the cure
(Tom Crane)

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Sun / Sony Monitor Model: GDM20SE20 / GDM-20SE2T5 (N2H Chassis)
Bright raster with flyback lines and reduced width, trips after 5 seconds
Replace the video drive ic on the a pcb located on the rear of the chassis around the crt neck, IC420 type CXA1907S, part no: 875207156
(Paul)

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Ibm Monitor Model: 6546-01N
Starts up OK from cold, but will not start when warm
Change C613 (47uF, 25V) Tant. and C602 (220uF, 400V)
(Simon)

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Fujitsu / Siemens LCD Monitor Model: CTM5010
VGA plug had been cut off at the PC during a burglary leaving no means of pinouts ID. Here is the correct configuration
Pin | Colour | Name | VGA Plug Pin No.
1 Purple SCL 15
2 Grey SDA 12
3 Black GND 5
4 Orange SGND 10
5 Yellow VSYNC 14
6 White HSYNC 13
7 Black RGND 6
8 Pink RED 1
9 Black GGND 7
10 Grey GREEN 2
11 Black BGND 8
12 Blue BLUE 3
(Simon)

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Philips Monitor Model: 3CM9609
Dead
Check R3121 (270Kohms, 1w, high voltage type) for open circuit which is located in the separate side mounted p.s.u
(Josh)

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Dell Monitor Model: 1028
Picture too wide / no trapezium / no controls of said functions
Change the fast acting diode D405 near the emitter circuit of the lopt transitor. This steals some of the flyback to feed a supply to the width circuitry
(Steve may)

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Iiyama Monitor Model: Vision Master (400/410 Chassis)
Picture comes on then moves quickly up off screen (vertical fault)
Change the vertical driver ic C1884CT (not the vertical output ic)
(Steve may)

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HP Monitor Model: Pavilion M70
Excessive width and no e-w correction
Modulator / damper diode (DMV32) had failed, these are available from Charles Hyde
(Thunderdunc)

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Mag Monitor Model: DX15T
Excessive Width / Pincushioning Problems
Check transistor Q203 (TIP127 - PNP Power Darlington Transistor). Check especially if Collector is internally short-circuited with Emitter. If so, replace it
(Francisco)

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Digital Monitor Model: VRCX1-W3
No light, no HT
Replaced two fast switching diodes (R4KL)
(Henk)

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Mag Monitor Model: DX15T
Dead, very low click - click sound heard from the chassis
Check Q105 if horizontal output transistor 2SC5129 and/or D104 fast soft recovery diode BD329-1200 are damaged (internal short circuit). If so, replace them
(Francisco)

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Dell Monitor Model: E551
Dead, yellow led flashing.
This monitor, only a couple of years old had been got at, a good fuse silver papered, a temper crack on the cabinet rear! It turned out the Chopper FET was shorted all ways & R618 o/c these were replaced & a good picture was the result
(Bob Meade, Suffolk.)

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Tce Monitor Model: M440
Não funciona e queima o Transistor de saída horizontal
Substituir o Capacitor Eletrolitico C430 (47uF, 250V)
(José Antonio Rodrigues)

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Acer Monitor Model: 7254E (15 inch)
Int loss of display, Power supply stable, all other sections are working properly
Replaced one 221, 2kV capacitor in the line output transformer section
(Rejeesh v p)

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HP M50 Monitor Model: D5258A
No display, ticking noise, green led is lit
Found Q402 Horizontal drive transistor (C3332) had failed, replaced with C3198, you can replace it with 2SC3198 or radio shack 276-2009 with care for the legs
(Mark Hanoun)

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Viewsonic Monitor Model: P815-1M
Dead / int
Bad solder on D855 located in power supply. You have to be sure to solder both the foil side and the component side of the board on the diode
(Mike Wilson)

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Compaq Monitor Model: 315U
Picture too wide
C434 (0.0047, 1.6Kv) located near fly
(Mike Wilson)

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Dell Monitor Model: D1025HT
Dim picture, looks like bad CRT
This is a common fault in this model and IC VPS12 is the main problem
(Imran Khan)

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Dell Monitor Model: M781P (CM2317 Chassis)
No picture, chirping noise, green light flashes
Replace MTP6N60 near flyback on large heatsink
(Wendell)

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Aoc Monitor Model: AOC (FCC ID: ARSCM3500 Chassis)
On switch on power LED flashing amber/orange, No Start up, but power available at main res capacitor C907
Check R904 for o/c (0.22Ohms), Q901 MOSFET (FS10UM) also shorted at all junctions. Use Equivalent IFR630 if Required
SAFETY NOTE: please ensure you discharge the mains reservoir capacitor before working in the area it will still have 300+ voltage charged. Use 10M Resistor on insulated crocodile clips and place on capacitor terminals. Ensure you remember to disconnect the resistor before switching on !
(Leon Guthrie - Electronics Technician), Borders college. Scotland)

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Belinea Monitor Model: 10-40-10 (MPR II Chassis)
Green power LED flashing, no picture, flashing diminishes slowly after swithing off
330v ok at main reservoir capacitor C105 (150uF, 400v), Check diode D057 (UF3004) or use UF5408 as replacement. This brought back the screen but was reduced in width. Q001 was also faulty (F630), replaced with IRF630 this cured the fault
(Leon Guthrie, electronics tech - Borders college. Scotland)

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Samsung Monitor Model: 551S
No power, fuse ok, noise from unit
Replace D606 and IC601 and it should be ok
(Maneco)

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Hyundai Monitor Model: V580 (C15R08050 Chassis)
No power
Check the KA3843B for failure
(Anonymous)

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Compaq Monitor Model: MV540
Dead with standby led going from green to orange as normal with no video input
The main PSU was dead but the standby psu was ok, R928 (620k) in the main PSU shutdown circuit was open circuit, its fed from the mains smoothing cap
(Owen O Reilly)

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View sonic Monitor Model: E40
LED blinking and no display
Q801 was short circuit and IC801 had failed, after replacing both the short was removed but the value of resistor R812 (.24 ohms) was incorrect, replacing resolved the fault
(Mohammad Akram)

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Hp m50 Monitor Model: D5258A (520X Chassis)
No raster or panel light, ticking noise
1.) Found Q502 Horizontal Output transistor had failed, Original part C5129, replaced it with type NTE2365
2.) Diode D509 had failed, Replaced
3.) Transistor Q104 was bad, Original part A1273. Replaced it with NTE12
4.) Q506 Mosfet transistor had failed, Original part IRF740. Replaced it with the same
(Anonymous)

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Ctx Monitor Model: PR711F
BANG! followed by smoke, still operating after failure (promptly removed AC main power)
Replace C137, a 47uF 250v radial capacitor, was visibly blown
(Anonymous)

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Gateway Monitor Model: EV900 (X19001)
Components VR501 (22K) and R573 (68k) in the ABL circuit burn out.
This is caused by the Flyback Transformer FEA-658. The transformer is available from Nikko Electronics @ £30 +VAT
(Ray)

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Apple Monitor Model: M9101Z/C
Dead
Check R3121 (270Kohms, 1w, high voltage type) for open circuit which is located in the seperate side mounted p.s.u
(Josh)

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Sony Monitor Model: GDM20SE2T5
Dark picture and jagged edges on both sides of the picture
Replace IC 007 on video board CXA1908S and replace all caps in the power supply (MUST do, all have high esr) Part can be ordered from www.powercomponents.nl, 1/3 of sony's price. Also check caps on other boards and cracks around the flyback
(Bart Bervoets)

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Viewsonic Monitor VP181 Model: VLCDS21544-1M
Back light bulbs not working
Repaired inverter board
(Anonymous)

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Sony Monitor Model: PVM1444QM
Top of picture is flipped
Change Q547 in the vertical circuit
(Francois)

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Compaq Monitor Model: 15FS
Shadow of one of the colour guns across screen (brighter on right)
Small electros (22uF) on neck board
(Anonymous)

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Kenitec Monitor Model: PX-14S
When cold picture jumps vertically
Vertical deflection IC (TDA1675) is temperature sensitive
(Jeroni Paul)

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Ctx Monitor Model: VL700 (1795VL)
Power led on, EHT rustles up normally but no display
Checks around the tube base panel revealed that the 6V3 heater supply was reading around 1 volt. Replacing C125 (1000µF, 16V) which was leaky cured the fault
(Simon)

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Essex Monitor Model: PV-7721M
Dead, 3A fuse blown
Check C510 & C511 (both 220µF 250V) for bulging can tops. If either is damaged, change both caps. Also IC501 (STR81145) will almost certainly be damaged and need replacing
(Simon)

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Mag Monitor Model: Innovision 570V
Poor horizontal linearity, display cramped at both sides
Check relay RL601 for dry joints and poor internal switch contacts. Replace relay with RS 198-6905 if required
(Simon)

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Ctx Monitor Model: 1569SE (Badged DAN)
Completely dead, no led lit
D407 (HER303) was short circuit, replaced with similar HER305. Also short circuit was Power FET Q401 (FS12UM-5), this is a 250V 12A device and proved difficult to obtain. Replaced with IRF644 (250V 14A). The monitor was now restored to normal working
(Simon)

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Belinea Monitor Model: 10 40 10
No display, green power led flashes, flashing slowly diminishes when powering down
D152 (UF1007) on secondary side of chopper transformer was short circuit. Replacing with a BA159 cured the fault
(Simon)

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Belinea Monitor Model: 10 20 10
Dead, power LED flashing and ticking noise
Q422 (2SC5297) Line Output Transistor was dead short. A replacement restored normal working
(Simon)

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Aoc Monitor Model: Spectrum 5ELR
Display wobbles, hissing noise from PSU chopper transformer
Replacing C907 (220µF 400V) cured the fault
(Simon)

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Kds Monitor Model: VS-7E
Dead set
Replaced Q412 type BU2520DF
(BenRose)

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Quantex Monitor Model: XP170S
Tripping - off/on switch ind led flashing
Replace Q712 (IRF630)-leaky all round
(Anonymous)

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Compaq 17" Monitor Model: V70
Image width / height increases / decreases
Replaced C851 (47uF, 250V)
(Alex Veltmans)

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Tiny Monitor Model: A1770
Raster too wide, will not adjust and appears bowed
Q423 and R411 replaced
(Geoff)

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Gateway Monitor Model: CPD-GF100
Field foldover on bottom of screen
Check capacitor C653 (470uF, 25v)
(Geoff)

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Dell Monitor Model: D1025HE
Dead. No HT on Line output Transistor
Change R414 (220k) in the collector feed to TR404
(Susy Brown)

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Sony Monitor Model: CPD-15SF1
Monitor shuts down just after pressing the power pushbutton, and the power on LED(green) and power save LED (yellow) both flash
The monitor started normally when pushing the power button twice. After troubleshooting found (Q001) spotkiller transistor was the reason, after replacement all was O.K
(Saudalhinai)

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Apple Mac Monitor using a Radius Card in a 20 inch monitor
Unable to set Resolution
Switch off Hold down 'T' button then switch on
(Roger - STS)

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Apple Monitor Model: 1710 (Sony Chassis)
No start or starting erratically
In the psu area Change the PTC (Burklin ref in Germany) and it's supply resistor
(Disco)

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Gateway Monitor Model: EV 700A (LG CA-65 Chassis)
This monitor which appears under many guises (LG CB775N, Studioworks 775 etc.) had very low width and severe E/W distortion. On screen H.size adjustment had no effect
Replaced R736 (100K, 0.25W) which was O/C
(John @ WTVV)

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CTX Monitor Model: VL700 (1769E)
Dead
Had nearly given up on this one till I got cct. for CTX1569! Original fault Q415 s/c and R474 burnt, no obvious shorts and replacements going same way shortly after switch on. Cause turned out to be C440 (10nF, 1kV) smoothing cap for G2 voltage leaky (reading 11K) also Q415 (BF488, used BF423 ok), R474 (33k, 0.5W), Same parts in CTX1569 are Q721, R761 and C733
Note there are different versions of this chassis depending on CRT and scan coil assembly type, one I had uses LG CRT and scan coil assembly and had board revision 11S31-069A REV: AS
(Kenny Cargill)

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Philips Monitor Model: 7CM5279/00T
White raster with flyback lines on screen
This was due to low collector voltage on the video output transistors, replaced R3570 (0.68ohm)
(Anonymous)

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JVC Monitor Model: TM1010P
Vertical scan collapse / horizontal black bars
Replace C416 with higher temp rating - goes low value due to proximity with v-drive heatsink
(Martin)

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Elonex Monitors
A common fault on these monitors is flickering lines about an inch or two from the bottom of the screen
The solution to this is very simple. The heat produced by the frame I.Cs heatsink destroys C313. Replace this on the underside of the pcb along with R308 (2.2ohms) which will also be open circuit
(Peter. E)

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Proview Monitor Model: 998M (PX-995 chassis)
Power Supply defective. Black lines on screen
The UC3842AN (KA3842B) was defectiveAfter assembling there was no picture
Bad solder connections were found on the CRT board (No Heater voltage)
(Winter)

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Hyundai Monitor Model: S450 (CKLS450 chassis)
Adjustment for v-size is limited. Vertical Raster is big. Other parameters are normal
Flash dead
(Roman)

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KFC / Smile Monitor Model CK1450 / CK1420
Dead
Replace R531 (560k)
(Duncan Newell)

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CTX 1765S Monitor
Over-bright display, with the brightness control having no effect.
R218, 390K, in the brightness circuit had gone o/c
(John Coles)




Source: www.e-repair.co.uk/tipsmon.htm

How To Test The Internal High Voltage Diode In Flyback Transformer

Myads

A leaky or shorted internal diode in the flyback transformer of a CRT TV or Monitor would cause the set to shutdown upon power on, power blink and even blowing some of the corresponding components like the HOT, B+ FET and B+ coil. Usually if the diode have a direct short circuit it will be easily detect by checking the connection between the anode and the ABL line using analog meter set to X 10 K ohm range. If the diode is leaky then it would be hard to confirm it with the analog meter.
In order to solve the problem you can use two analog meter set to x 10 k ohm and connect the meters like a battery in series an then test from anode to any of the flyback pin. A good diode will usually have only reading. If there is a pin that shows two reading then the internal diode had shorted. It is as simple as that!

Troubleshooting and Repair of Computer and Video Monitors

Myads

Here I Saw a useful link in the internet about repairing a Computer Monitor, containing his experiences in repairing a computer monitor and put in the web his knowledge thats he gain.

Notes on the Troubleshooting and Repair of Computer and Video Monitors

Monitor Repair

Myads

View here some of the notes and common question and answer about repairing a monitor, click the link below. They are based on experience of the one who wrote that articles

Monitor Repair

LCD Backlight Conversion to LED - StumbleUpon

Myads

Learn how to convert the CCFL Backlight of your LCD Monitor into LED.

LCD Backlight Conversion to LED - StumbleUpon

How To Repair ACER AJ17 Monitor With Horizontal Size Problem

Myads

How To Repair ACER AJ17 Monitor With Horizontal Size Problem

This Acer AJ17 Monitor came in with the complaint of wide screen and distortion (line swimming) across the vertical line of the display. Although you can adjust the horizontal size, you just can’t make it into smaller and the horizontal size still big and curve inward.

You could also clearly see all the vertical lines at the display have a small wave (distortion) across it. At first I thought it was caused by a defective filter capacitor at secondary side of the display but all the capacitors checked to be okay.

Since all the caps tested okay, now I fully concentrate on the horizontal size and pincushion circuit area. If there are any components shorted or faulty in this area, it will cause the display to go big (wide) and many times you can’t tune it back to normal size. From experienced, mostly the problem was the modulation diode that have shorted or a pincushion transistor that have leaked.

But both components and all the nearby circuit components checked to be okay too. Using high voltage probe to test on the anode voltage proved it to within the right range. For your information, if the holddown or safety capacitor capacitance value out it could also cause the display to turn big but of course the high voltage measured at the anode cap would be higher.

Since all the suspected components measured okay, I would then use voltage testing to locate the fault. Just before doing the voltage test, I observed that the eeprom ic is installed just beneath the picture tube. If any eeprom ic in any monitor located under the belly of the CRT, then chances are high the data would be corrupted by the discharge of the CRT.

If you repair some of the latest model of Samsung Monitor, you will understand why because the Samsung monitor had a piece of aluminum shielding to protect the microprocessor and eeprom IC from being discharge onto it.

A corrupted eeprom data could cause the micro processor to output a wrong signal to certain or all circuit. If it send a wrong signal to the DPMS circuit, then the monitor will shutdown once the power is on.

The ACER AJ17 eeprom IC part number was 24C08. I used to keep good eeprom data in my hardisk for future use just in case if there is a need to reprogram the eeprom IC. I took out the eeprom IC from the board and insert it to the center socket of the pony prog eeprom serial programmer.

I then connect it to the serial port of my computer and begin to look for the good data for this model. I do keep a lot of ACER monitor eeprom IC data.  Once I got it, I overwrite the old data with the good data.

Installing back the eeprom IC took only a while and the Monitor was switched “on”. Guess what? Not only the horizontal size now got back to normal, the distortion at the vertical lines vanished too. You better believe it that a corrupted eeprom IC could cause many weird symptoms. For some monitors, once the eeprom IC have been programmed, although the monitor work, the color may run. Some techs are good in changing the code in the data and tune to the desire colors.

In order to make the new reprogrammed eeprom data last longer, you can add a piece of shielding on top of the EEprom IC to prevent any loss data in the future. Bare in mind that, eeprom data loss not only occurs in monitor, it could happen in other electronic equipment too such as LCD Monitor, Television, UPS and etc. Whether you are repairing the ACER AJ17 or any other brand of Monitors, if you come across any weird problems that you can’t solve, try reprogramming the eeprom IC and who knows the monitor may work again. In order to do this, of course you need a serial programmer which you can easily buy one from the internet.

Troubleshooting And Repairing Sylvania LD320SS8 LCD TV With Shutdown Problem

Myads

 Troubleshooting And Repairing Sylvania LD320SS8 LCD TV With Shutdown Problem

 

This is a common LCD TV that we see for repair. The failure symptom is almost always that the TV will turn on for just a moment, “digital television” is displayed in the lower right corner and then the TV shuts down and goes back into standby mode.

This type of failure is almost always caused by a power supply or inverter circuit failure in the majority of LCD TVs. Normally I would start by measuring output voltages from the power supply during the moment it is on to see if any are out of tolerance or missing especially the output to the inverter circuit, inspect the PCBs for solder connections with ring cracks and check the power supply secondary side filter capacitors for raised ESR and check the pico fuses and transformers on the in the inverter circuit etc.., but with this model I know that one of the HV transformers in the inverter circuit often develops an open secondary winding, typically it is  the HV transformer at location T1100. 

The first thing I do with this model is check all the secondary windings to see if any have opened by measuring there resistance, an open winding will have an infinite resistance or if you are using a DMM you will get an O.L. (Over Limit or Open Loop) reading. Each one of the HV transformers in this model TV has 2 secondary windings. 

 

While measuring the resistance I found that none of the secondary windings had opened, but what I did notice was that one of the secondary windings had a much lower resistance that then all the others I measured. All of the secondary windings had a resistance of between 522 and 527 ohms and the suspect secondary winding had a resistance of 495.4 ohms, about 30 ohms less than the rest. This was a very good indication that this secondary winding had shorted turns. This is what's great about testing the HV transformers in most LCD TVs, being able to compare the test results of one transformer against the others as typically only one of the HV transformers will go bad and it will be easily identified when tested and compared against the others. 

Upon closer inspection of the transformer with the shorted secondary winding the burned area of the secondary winding was noted as well, confirming without a doubt that the transformer was faulty and sure enough it was T1100, the transformer that we normally replace in this model but always for an open secondary winding but this time obviously the winding was shorted. Most likely what typically happens is the secondary coil shorts and then excess current is drawn as the resistance of the coil drops which in turn causes the coil to heat up and burn causing it to go open, but in this case the coil shorted and the TV shutdown before it had a chance to open. 

After the HV transformer was replaced with a new one, part number LTZ2PC0MS008(substitute for 3PC0XB001) the TV turned on and functioned properly once again.

The LTZ2PC0MS008 can be found at Electronica USA along with many other electronics components. 

Hopefully you all enjoy this article and special  thanks to Jestine Yong for giving me the opportunity to do a guest post this month. Best wishes to all the ERG members. As always I can be contacted by emailing me

john@preher-tech.com

source: electronicrepairguide.com

How To Repair LG 710E CRT Monitor With Power Blink Problem

Myads

How To Repair LG 710E CRT Monitor With Power Blink Problem

LG 710E 17” CRT Monitor came in with the complaint of power blink. A power blink problem can be cause by either in primary or secondary section or even in both sections.

A defective power IC, power fet breakdown when under load, high esr in electrolytic capacitor, increased in current sense resistor value, a shorted zener diode, a leaky transistor, open circuit or resistor has changed value in primary side can cause power to blink.

As for the secondary side, a shorted secondary diode, flyback, HOT, horizontal yoke coil, damper diode, B+ fet, an open filter capacitor, shorted IC and etc can cause power to blink as well.

Normally what I do is to remove the B+ fet first and connect a light bulb to distinguish whether is the primary or after the B+ circuit components that caused power to blink. However in this case, I did not put the light bulb and I directly removed the B+ fet and power on the monitor. For your information, this B+ fet is the N-channel mosfet and this B+ fet is part of the boost circuit. 

After removing the B+ fet, not only the power didn’t blink, there was display as well and the anode voltage reads about 12 Kilo volt (a good monitor should have about 24 KV). The reason why you got 12 kilo volts is because the boost circuit is not functioning due to the removal of the B+ fet. The display shown a small width and the horizontal size control is already set to the maximum (you can’t get maximum width because the anode voltage is only 12 KV). You can control or set everything in the On Screen Display (OSD) except you can’t bring horizontal size to maximum.

With having a display, it is a good clue to me because I knew that many circuits is working such as power section (so you don’t suspect primary side anymore), flyback transformer, yoke coils,  micro-p, eeprom, horizontal and vertical circuit, color circuit and even the Osd circuit. Without the B+ fet, there is display but with B+ fet the power blink. In this case, one would always check the B+ fet first am I right? However the B+ fet turned out to be good!

Now where is the culprit hiding? Troubleshooting sometimes can be very frustrated and most of the time is always fun. One of my methods that I liked to use is to touch for any unusually hot components on board with my finger. (Please take note for all electronic repairers-switch off and unplug the power cable and discharge the big filter capacitor in primary side before you begin to touch any components).

Usually after power off, I would touch on the flyback first then to other components surrounding the high voltage section. While browsing the components with my finger I stumbled upon a resin coated ceramic disc capacitor which is quite hot. It is located near the flyback transformer and in fact the capacitor was there is to act as a filter capacitor for the 400 vdc line output as shown from the photo.

After the cap was removed and checked with an analog meter, it showed a shorted reading even in the X1 ohms range. A good capacitor should show a charge and discharge activity in the X10 k ohms range. A new capacitor replacement for this LG 710E 17” CRT Monitor cured the fault.

The reason why the monitor power blink is because the faulty capacitor become shorted when in full operating voltage (boost circuit is functioning and approximately 60 -70 vdc enter the B+ flyback pin). When the B+ fet was removed (boost circuit not working and only about 40 vdc enter the B+ pin of flyback) the monitor is not working under full operating voltage and the faulty capacitor can still tolerate (partial short) and became hot. I believe if the monitor is switched “on” for a little longer, it would cause the capacitor to develop a direct short circuit and if this happen, removing the B+ fet to test the monitor would not make any different (the power would still blink).

Monitor Color Problem-How To Repair LG 710E Monitor With A Missing Blue Color

Myads

Monitor Color Problem-How To Repair LG 710E Monitor With A Missing Blue Color

If you think that electronic repair is very difficult to learn then you have to read this article where only by using a solder gun could solve a Monitor problem. Of course there were many tough dog cases (very difficult to find out the fault) in electronic repair but at the same time there were also many cases that can be solve by some simple ways.

This LG 710E LG Monitor came in with no blue color problem. How do I know if the blue color was missing? Simply run a color test (that you may also download from the internet) or from a Monitor testing program generator, you could clearly see as which of the color is missing when you run the color bar test.

A missing blue color in the Monitor could cause the display to turn yellowish. Troubleshooting color problem is one of the easiest in Monitor repairing. Whether the missing color is from blue, red or green there are some areas that you need to check in order to successfully repair it. Here are some of the points that you need to check:

- A bended color pin at the VGA connector. (If pin one is bend then there would be no red color)

- A defective VGA signal cable. If the internal wires were broken then there would be missing colors. You can check if the signal cable is good or bad by doing a continuity test using a multimeter.

- Dry joints in the CRT board such as in the CRT socket pins, video pre amp and driver IC and even at the connector pins. In fact this problem contributed about 80% of Monitor color problems. Applying fresh solder would usually solve the color problem.

- A defective IC either in the Video Pre-amp or Video Driver IC.

- Faulty components in the CRT board. It could be a shorted driver transistor or even electrolytic capacitors that the ESR reading had shot up!

- A bad CRT socket. Sometimes decayed glue could cause the internal pins rusted and thus affecting the colors. Replacing only the CRT socket would definetely solve the problem.

- A weak or a defective picture tube (CRT tube). Yes, I do came across one of the electron gun (most probably the cathode materials had used up) in the tube faulty caused a missing color in the screen. There’s no way to repair this type of problem-the only way is to replace the CRT tube.

- In the newer type of Monitor, color setting is save in the EEPROM IC . Thus, if the EEprom data is corrupted, you would also get a missing color! The only way to repair it is to reprogram the IC or use a soft jig to tune it back the color setting.

Now, which one of the above is the easiest to start with first when comes to troubleshooting the color problem? I believe you would agree with me that the first, second and the third are the easiest compare to the rest. Normally I would hit the Monitor with my bare hands to see if there are any changes in color at the display (be careful not to hit too hard till the casing broken). If there is a change or flashes then I can say that the Monitor has dry joints. And if it stills the same no matter how many times I hit it, I will then starts check the VGA connector and the cable.

In the above Monitor, the problem was dry joints because when I softly hit it with my hand at the side of the Monitor, the blue color immediately appears. The aluminum shielding at the CRT board was opened and I could clearly see lots of dry joints especially in the video pre amplifier and the video driver IC. When you resolder please don’t just touch on the IC’s only, you need to resolder others area as well like the CRT socket pins. Doing this would prevent any color loss again in the future. A good job would prevent call back and to save you time and money and most of all your reputation!

 

After everything was done, you then need to gently knock at the CRT board again with the plastic handle of the screw driver to see if the color problem still exists. You may also knock on the main board just incase there is any dry joints there. One more thing, if you find that the Monitor is a bit dusty, you may use a vacuum cleaner and a brush to clean up the dirty area. 

Whether you are repairing the LG 710E or any other brand of Monitors, if you come across color problems, you can always use the procedure above to find out the fault. If the VGA signal cable is okay and there were no dry joints in the Monitor, I guess the only way is to use voltage testing method and start checking components with your tester or meter.

How To Repair Dell 17" (Likom L705XXX) Monitor With No Power Symptom

Myads

How To Repair Dell 17" (Likom L705XXX) Monitor With No Power Symptom

This DELL 17” Monitor (Made in Malaysia under LIKOM model L705XXX, product no: L7055LP) came in with no power symptom. Normally after opening up the cover I would look at the power supply (primary side) for any burnt and cracked components first.  If there are darkened area and burnt components, I would tell myself that this Monitor needs a little more time to repair it. If it is not (component’s intact) I would usually begin to discharge the filter capacitor and start checking the fuse.

Okay, it is confirmed that all the primary side components looks good in this Monitor.

First, discharge the big fat filter capacitor with a resistor (I know that the voltage already drained off but it is a normal procedure for me because what if the start up resistor has an open circuit?) then check the fuse.

If the fuse is okay, experience will tell you that the bridge diodes are also working fine. Place your black probe of your analog meter set to x1 to the center pin (drain) of the power FET and red probe to the other pin one at a time (gate and source). If the pointer of the meter doesn’t kick then 80 % of the Power FET is okay. If you want to 100% confirm if it is good then you have to solder it out and test. If the pointer shows a reading then most probably the power FET has developed a short circuit. The result that I got from this Monitor was the pointer don’t flick.

Now is the time for me to use the dick smith flyback tester to check the smps primary winding. The result that I got was, the led bar don’t lit. Ah ha! That was a clue and this clue tells you that it is either the smps primary winding is shorted or one of the secondary diodes has given way. Of course you can check all the secondary diodes with your normal multimeter first (remember, every electronic repairers have their own procedure methods of troubleshooting) but I prefer this way as I want to confirm also if the smps primary winding is working or not.

Usually smps transformer is very robust thus I didn’t suspect it to pull down the flyback tester reading. I straight away check all the secondary diodes with my analog meter and found one diode shorted (part number U202G). Since I do not have this part number, I use a UF5404 ultra fast recovery diode as a replacement. In fact I use this UF5404 to all 14 to 17” Monitor as a replacement for all part number of secondary diodes. The spec of this diode was 400volt, 3 Amp with 50 nanosecond.

 

After the replacement of the diode, and placing the flyback tester probes again to the primary winding, the result shows full bar on the LED. Don’t be happy with the result yet because your job still hasn’t done.

Now I moved on to check HOT with the same procedure as checking the power FET. The HOT checked to be okay too. Next, I check the internal capacitance of the flyback transformer to see it is shorted or not or is the capacitance value run. For your information, internal capacitor in flyback transformer gave lots of problems in computer Monitor. I also scanned thru the B+ FET and found it to be good too.

Now is the time to switch on the Monitor, however this round I don’t connect any bulb because it was only a shorted diode in the secondary side. I would only connect a light bulb after repair when there is major short circuit in the primary side such as a blown bridge rectifier, shorted fet and smps primary winding and also burnt components in the board.

The DELL 17” Monitor worked beautifully and after long hours of burn-in test, I declared it okay and ready to send back to my loyal customer. Isn’t it fun to be able to repair a Monitor and at the end you get paid for something you like doing. I just love electronic repair!

How Cathode Ray Tube Work And Explanation

Myads

How Cathode Ray Tube Work And Explanation

     It is important to know how a cathode ray tube work and its explanation. Whether you are in the monitor or tv repair, i'm sure you had came across picture tube that has gone dim and no display. Every electron gun has it life span, i still could remembered there was a picture tube that had a very dim display and the monitor was about 1 and a half to 2 years old only. Some picture tubes were designed to last more than 15 years! If you truly understand how electron gun work, you can perform some modification to brighten up the crt. Some technicians suggest to increase the heater voltage to burnt off the contamination while others just used their own home made crt rejuvenator.

Short Circuit Between The Screen (G2) and the Control Grid (G1)

Myads

Short Circuit Between The Screen (G2) and the Control Grid (G1)

Dear Jestine: I have a very interesting question about whether we can use the same method of blowing away a short between the focus grid and the screen grid and apply this method to the shorts that can happen between screen and control grid or for example or the control and cathodes .....if so then I would use it to increase the possibilities of saving a CRT tube bye for now. Wael Fathe

 

Dear Wael: If the CRT screen grid (G2) and the control grid (G1) shorted internally it could cause the Monitor to have no display and even if have display it will going to have bright display with white flyback lines across the screen diagonally. The method that I had shared to all of my ERG members was to remove the shorts between the screen (G2) and the focus grid (G4). To answer your question, yes there is a possibility that you can use the same method to blow away or remove the shorts between the screen and the control grid.

However there is a risk because the control grid (G1) is located very near to the RGB cathode. In other word, if you use the method on this screen and the control grid, I’m afraid you may blow away a good RGB cathode (cathode material drop out from its location because of the high voltage across it) or even causing short circuit between the control grids with one of the RGB cathode. If this happens the Monitor will be going to have a missing color or even a bright display with flyback lines across the screen.

There is no harm trying it, after all the CRT is already confirmed to be not working. Let your customer know first the consequences before begin to blow away the shorts. If you have a ready spare tube for replacement I suggest you to try it, who knows the short might be removed with just a single discharge!

Viewsonic Monitor Problems-CRT or The Degaussing Circuit?

Myads

Viewsonic Monitor Problems-CRT or The Degaussing Circuit?

This Viewsonic 15” Monitor came in with the complaint of color problem in the whole display. Some techs called it as rainbow display while some referred to it as color patches fault. This problem usually were related to a bad picture tube (due to a fall that caused the internal shadow mask to come out from the original location) or from a faulty degaussing circuit.

The degaussing circuit consists only of the Posistor, degaussing coil and a relay (depends on designs). Digital Monitors are using the microprocessor to trigger the relay through a NPN transistor (C945) in order to activate the degaussing circuit.

 

Now, whenever I see this problem I would normally first use a demagnetizer to degauss (to make the color problem (purity) to be even again). If the Monitor color patches still remain the same (no changes) then it is confirm that the Monitor CRT is at fault. There is no way to solve the bad CRT problem unless you replace it with a used or a new pc tube. If the display color can get back to normal again, then most probably the degaussing circuit has problems.

Some common problems that can happen in the degaussing circuit were dry joints (very high percentage) especially at the leads of the Posistor and a defective Posistor. You can’t test a Posistor with a normal multimeter. The only method to check it is direct replacement and retest again to see if the color problem symptom has gone away or not. If you can’t find any dry joints in the degaussing circuit, chances are very high that the Posistor may have problem. Sometimes you can remove the Posistor from the board and shake it to hear if there any loosen materials inside the Posistor. A good working Posistor should not produce a loud noise.

As for the degaussing coil, you can easily unplug the coil and test it with an ohmmeter. I came across before an open coil but the problem was very rare. You may also test the degaussing coil with the Dick Smith flyback tester. A good coil should show at least 3-4 bars and above! Assuming the problem was can’t degauss the picture tube and the Posistor and the degaussing coil you had checked to be okay, then suspect a bad relay or the circuit that trigger the relay. It could be the microprocessor is not sending the signal or the faulty NPN transistor along the circuit.

Overall, color patches problem is not difficult to repair but you must understand how the circuit works first. Many times, Monitor repairer confused about the symptom. For example- if you could see a display (character) with color patches then it is either a bad CRT or a degaussing circuit. If you could not see the display character but with color patches then suspect a defective vertical section. I had solved lots of the problem (no display character but with color patches) by changing the vertical IC and resoldering the circuit. Please take note on this complain! The Viewsonic Monitor problem that mentioned above was actually solved by replacing only the Posistor.

How To Repair Likom Monitor With No Display Problem

Myads

How To Repair Likom Monitor With No Display Problem

 

The complaint for this LIKOM 15” L4031NDG Monitor was no display and has power. Well, no display can be no high voltage, failure in G1, G2 and heater circuit, defective flyback transformer, failure in picture tube and microprocessor or many other reasons . In order to find out the answer we have to switch on the Monitor. Upon switching on the monitor, I could not hear any sound from the monitor but the power led is on (green light). You can’t feel any static at the glass of the picture tube. This could be a sign of no high voltage symptom.

 

 

Anyhow, I have to use my faithful Kaise SK9000 high voltage probe to check if the high voltage present at the anode. Sometimes if you can’t feel the static at the glass of CRT, doesn’t mean that the high voltage is not present. It’s only low in high voltage; say may be 10 to 12 kilovolts. Low high voltage and no high voltage are totally two different symptoms. In the above case, my high voltage probe registered zero volts! So it’s confirmed no high voltage problem.

There are many reasons for no high voltage problem. A missing B+ voltage, a defective flyback transformer, no horizontal drive pulse from h/v oscillator ic, low or missing supply voltage to horizontal driver transformer and etc could cause no high voltage. The first point that I have checked was the flyback internal capacitor-the capacitance is within the normal range which is 2.7 nanofarad. If the internal capacitor is shorted, it would cause no high voltage. The second point that I have checked to be okay was the B+ voltage. It showed about 50 + volts and this mean there is supply entering the B+ pin of flyback transformer.

When checking the third point (the voltage at the primary winding of horizontal flyback transformer), I found that it has zero volt which is very unusual. The base drive power supply input has about 14 volts but after the resistor it showed zero volts (by right it should have about 12 volt-voltage drop after the resistor). When I placed my finger on the base drive power resistor just after switching off the Monitor, I could felt it was very hot.  Now this is what we call a clue. A good working base drive power resistor won’t get hot till it burns your finger! There must be something that has gone wrong or shorted that makes the power resistor turned extremely hot. From the result we get, we can say that the horizontal drive circuit is having problem so my concentration is on this circuit.

A shorted horizontal driver transformer primary winding, horizontal driver transistor, components surrounding this circuit could cause the power resistor to turn hot. The horizontal driver transformer primary winding can be check by using a dick smith flyback tester while the horizontal driver transistor and surrounding components can be test with a normal multimeter. The result, surprisingly not even one component in this circuit found to be faulty.

Since I could not locate the defective components, the only way to find out the culprit is to come out with my own schematic drawing base on this monitor circuit (using monitor circuit theory to solve problem).

When the monitor is turned on the h/v oscillator tda4858 will receive a supply voltage about 9-12 volts from power supply. Then it will send a square wave pulse to horizontal driver transistor through pin 7 (horizontal driver output) to cause the transistor to switch. Once the horizontal driver is switching the horizontal driver transformer would work and a base signal was produced to turn on the Horizontal output transistor (HOT). This HOT would then drive the flyback transformer and 24 kilovolt would appear at the anode.

I asked myself what if the h/v oscillator ic tda4858 instead of producing a square pulse, it produce a constant signal? If it sends out a constant 5 volts signal to the horizontal driver transistor, then this transistor would not switch and causing it to turn “on” all the time. If this happen, the base drive power resistor and the horizontal driver transformer primary winding would suffer. The base drive power resistor and the horizontal driver transformer primary winding now would acts just like a filament or a lamp!. No wander the base drive power resistor was getting hot when the monitor was turned on.

After carefully studied the horizontal drive circuit, I’ve made the conclusion that it was the h/v oscillator tda4848 that sends a wrong signal causing the base drive power resistor to get hot and at the same time causing no high voltage in the monitor. I did not use an oscilloscope to check for the square wave in order to prove my theory right because I’m very certain that it was the h/v oscillator IC that output a wrong signal that caused no high voltage.

You would not believe this; yes it was this culprit (TDA4858) that caused no high voltage problem. After replacing the IC, the high voltage immediately energized and the zero volts measured at the pin of horizontal driver transformer now showed 12 volts! What a relieved and a great satisfaction in my heart. I believe if we continue to switch on the Monitor for a longer period, either the base drive power resistor or the horizontal driver transformer primary winding would burnt out causing it to open circuit.

Repairing Monitors need patience, understanding how Monitor work and its signal and also the right way to test electronic components. If the practical way can’t solve a problem, you can always use the theory way to help you out. Thus it is important to know on how to read a monitor schematic diagram. Don’t give up and continue to learn and I believe one day you shall achieved what’s desired in your heart! Have a good day!

Likom L4031NDG Monitor