Panasonic Plasma TX-P42GT20E - massively damaged SC board TNPA5081

I got this nice 2010 Panasonic 3D plasma from eBay classifieds.

The seller reported that the device won't start and blink 10 times. I pulled the service manual from elekrotanya.com and looked it up:

Wow. That's a long list of possible failures! As the price was ok I dared to go for it.

The service manual is a delight. The best I have ever seen. Schematics and layout of all(!) boards are in zoom-able vector format. There are block diagrams, which give you a good overview of the main components. Very thorough diagnostic and miscellaneous service information. This is what you get from a manufacturer who does everything himself and not buy from others.

Back cover removed and the usual excellent Panasonic build quality shows:

The difference between this 2010 model and the 2011 Neo Plasma TX-P42ST30 I repaired earlier this year is significant. Everything is much bigger and clunkier. Even though the circuitry is probably very similar, the large semiconductors in this one are still through-hole as opposed to SMD in the later model. Cooling is passive with large heatsinks without fans.

So, my first check on a Plasma always goes to the SC board. But what's this?! A diode and transistor are missing! The cheeky seller did not tell me about that. Bastard. That was the reason for the 10 blinks in the first place, but what's the rest of the story? So I began measuring. I found those parts to be dead:
missing: D482, Q452
short: Q421, Q422, Q403, Q402, Q521
burnt, open or off-value: R421, R551, R522, R521

From that point on I did not bother investigating any deeper. After plowing through this thread in the Badcaps forum I realized that the SC board was severely damaged and a complete overhaul was the only option besides getting a used, working one. The board has the tendency to blow up again if not all of the dead parts are properly replaced.

The repair kit from GTV Watford in the UK, which is a very good source, costs 84€ including shipping and is a hell lot of work (27 parts). Luckily, I also found a board for 68€ from an Italian on eBay.

That board had one rub though. It was the AY type for the 50 inch 3D panel. I needed an AH type. What's the difference? See for yourself:

The only differences I found were the coils and the capacitors around them. The green and blue big drops and one electrolytic. A guy in a forum explained that this circuit is tuned in resonance with the individual panels to suppress electromagnetic emissions.

The board from Italy measured flawlessly. To be safe that none of the Y-buffers had killed the SC board, I removed all the panel connectors and measured the buffer outputs for shorts as well as the pins on the connectors to the SC board. No findings.

Now, to morph the AY into the AH type I swapped out the differing parts.

Board put back in and the TV worked. Almost. Because I removed the panel connectors, I had to go through the incredibly tedious routine of refitting them, which never works at the first attempt. The latches of the sockets on the buffer boards have the tendency to push the flat cables out of their position. Horizontal black lines and blocks all over the screen was the result. After 20min of trial and error everything was sitting were it should and Frau Johansson looking gorgeous as ever.

This older generation of Plasmas does not have the stunning image quality of the 2011+ Neo Plasmas. It is interesting that the image looks "analog", as if a CRT TV was pimped for HD. Nowhere as overly crispy digital and bright as modern LED LCDs are. It is pleasantly smooth and totally natural. This model also has an expert mode with countless image adjustments.

So, this adventure once again confirmed my impression: Panasonics are the best. Period.

Acer at3720 - no standby voltage - shorted FET FQPF7N80C and PWM IC DAP006

Acer used to build TVs. Didn't know that. Actually, it is the same as the Sanyo DP37647. A real oldie :-)

The set showed no signs of life. No standby light, no reaction to the power switch.

It is built like a monitor, with uncountable screws and a full metal cover over the boards. And it has reasonably sized speakers! :-)

I quickly found the 5V standby voltage to be missing completely. I removed the power supply and connected it to the isolation transformer for further checks. Never work on switching power supplies without an iso transformer!

The main reservoir caps were fully charged with over 300V. The FET, which controls the primary winding of the stand-by transformer had a short between gate and source. That's not good, because it switches the full main voltage and the PWM control chip is connected to the gate. I suspected that the chip did not survive this attack.

To be sure that a shorted transformer primary winding wasn't the reason for the dead FET I used my ring tester. Two green LEDs indicated a perfectly fine winding.

Well, I first replaced the FET, which is a cheap standard part. Not working. There was no voltage at the source pin. The whole stand-by section had no voltage anywhere. Tracing back to the main capacitors I came across a blown 0.1 Ohm resistor hidden under the large aluminum cooler. It is used as a fuse for fatal failures, I think, and cuts off all power sections. For testing I only had a 0.22 emitter resistor from an amplifier. Still not working. 

The PWM chip read DAP6A. I couldn't find anything under that type, until, after some research, I found out that it is actually called DAP006. Datasheet was available and I probed the chip. Uh oh, it had a short between ground and Vss. 

Thanks to ebay I found (only!) one dealer in Great Britain for the chip and one for the resistor.

The replacement chip worked fine and the TV is back alive:

Three parts replaced this time:

Philips 37PFL5603D - washed-out colors - AS15F chip defect - TCON board T370HW02 V402

Some repairs are becoming a routine like removing the appendix from the bowel. This TV showed all signs of a defect gamma chip on the TCON board. In most cases a solarization effect is produced by a broken gamma chip. Here though, the colors were almost completely gone (the moiree pattern does not exist in reality):

This device is from the golden age of LCD TVs (around 2008/2009). It is built like a tank. With its 25kg it trumps modern 46 inch TVs. The capacitors are all top quality and showed no signs of aging whatsoever. All wires are protected by sleeves, the boards are mounted on an extra frame. In modern TVs, they are screwed directly to the backplane of the panel.

Those HDMI ports will never break off:

You don't see this type of LVDS cable anymore. Solid plugs, massive sleeve and shielding. Not this cheap arse flat wire crap like today.

Removing the TCON was a bit tedious because the frame was in the way and I needed to lift it with one hand while loosing the screws with an extra long screwdriver with the other hand, pointing through the holes.

The infamous AUO type TCON board appeared. They are known for AS15-F gamma chip defects. The Samsung LE37B650 I fixed a couple of months ago had one of those, too. The chip is hidden under a heat conducting block, which needed to be replaced afterwards, because some material got ripped out when I pulled it off. To conduct heat properly, its surface needs to be smooth.

How can you measure the AS15 gamma chip? You locate the gamma voltage test points on the board and they should show a continuous stepwise increase / decrease of voltages from VGMA1 to VGMA21. Any test point with no voltage (a few millivolts) or a large gap is a sign of a broken AS15. In this TV, I tested VGMA1 to 5 and got nothing. I didn't bother testing the other voltages, as this was a clear case.

With the help of my pre-heater plate at 170°C and the hot air gun at 420°C the chip came off like a charm. On this board, it is not soldered to the ground plane for heat dissipation.

I screwed up the first replacement and the picture was even worse. Either the chip was dead on arrival or I broke it while trying to solder it with paste. The next one I soldered with the iron and plenty of Chip Quick flux (my favorite!).

A new heat conducting block attached to the chip and the board was good to go. On the picture you can still see the protective plastic film, which I almost forgot to peel off :-o

The colors came back alive:

Hallo Frau Johansson!

So, this was a quick and easy fix for as little as 10€ (including the failed first attempt). Not bad at all.