LCD TV System Block Diagram

Myads

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

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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

TV REPAIR GUIDE: How To Repair Emerson 32” LCD TVWith No Power And Shutdown Symptom

Myads

How To Repair Emerson 32” LCD TV With No Power And Shutdown Symptom

The first problem was no power at all (no indicator light) so I inspect all of the diodes in the power area and found 2 shorted diodes D503 and D505 and both were 1N5406. I replaced the diodes with exact part number and now the TV could power on but picture shutdown and sound is good. I knew this was a backlight problem, so I tested all the transformers on the inverter and found 2 high voltage transformer that were open at the primary T1100 and T1050. I replaced both with exact type and now picture comes on and then shuts down again after less than 1 minute.

I continued to test and trace and found a bad mosfet Q1102 (22N055). It was tested good out of circuit but when under full operating voltage the mosfet would fail. By replacing the 5 components- 2 x Diodes, 2 x High Voltage Transformer and a Mosfet cured the problem. I left the TV on for 5 hours for burnt in test and the TV worked perfectly good.

Here is a tip for you- when using an analog meter in the OHM scale (x10K) the test lead voltage polarity is switched, this means the positive lead (red) is negative voltage, and the negative lead (black) is positive voltage. The test lead voltage in (x10K) scale is 13 volts

 

which is very good considering this meter only cost $49.00 from MCM Electronics. This voltage is very good for turning on various components, but for some diodes this voltage can damage the PN junctions.

This article was written by Damon from the beautiful place Maryland USA. His position now is Senior Electronic Technician (TV Repair) and soon will be involve in the robotics technology. He has many secret repairs he’d done on plasma/LCD TV and he need to find the time to write it and post it on his websites. He welcomes any technician or engineer who is willing to connect and share information concerning electronic circuits, component science, and R&D.

Here are two photos of all the TV's that he need to repair-its a lot, in fact over 700 plasma and LCD TV and over 200 DLP TV and Rear Projection TV's to fix.

LCD REPAIR: The LCD screen does not light

Myads

The LCD screen does not light

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One of the most perplexing failures of LCDs, is when he turns on the power light turns green, as if normal, but the screen does not light and no image appears ... Thus, at first glance, have no clue to the possible cause, because it can be everything. A first step before starting to dismantle everything at random, at least, is to check if the motherboard is sending image.  But as if nothing appears on the screen? Well, we can not see it, but if it is being generated, be it '. To see it, we need to illuminate the screen, as they would fluorescents.  At this time, comes into play a simple, powerful and small flashlight LEDs. To reach a window behind the LCD screen, we need to do a partial disassembly of the device.  So already with access to the back of the screen, turn on the monitor is already connected to a CPU, where an image is being generated and light up any window with his flashlight.  Looking at the screen in front, we note the presence of the image. By exclusion, we now know is that the possible cause or in lighting or source. Then proceed with the tests to detect the presence and balance of the MAT in the output of the inverters and verification of fluorescent lamps, to resolve the defect. If, on the other hand, there really is no image, then the research question involves the motherboard monitor. Are you interested in purchasing a flashlight Led?  See more details about it by clicking here

MONITOR REPAIR: LG did not leave the screen saver

Myads

LG did not leave the screen saver

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Q: In my workshop, and a sta monitor LG FLATRON W2043S model with the following default: normal league, when you put a sign makes the message POWER SAVING MODE. I checked the source and everything ok. I noticed that this also happens with other models. What might be the cause? A: This means that the monitor is not detecting the sync signal from horizontal or vertical. The cause may be a defect in the signal cable (check wiring on pins 13 and 14). But if the circuit monitor, the cause should be near the Mykonos, a transistor or fusistor pifado line circuit horizontal or vertical. If not, it is the Micon.

LCD REPAIR: Replacing the Micon NT68F63LG

Myads

Replacing the Micon NT68F63LG

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The explanations were formulated for the chip SMD Novatek , but apply to all other MDSs similar . Removing the chip Take the edge Adjust the sides lightly to hold the chip Fit and use the heat gun For release without forcing Remove the excess with a fine mesh Welding the chip Position it correctly (notice the angled corner) pins and solder the ends to lock the chip Place a solder dross and go pulling iron Until you reach the opposite end. Repeat with the remaining 3 sides If the last pin stick together, remove excess with a sucker. Veirifque if there was no residue of tin between the pins or pin loose Rise