Philips 22PFL-3606H/12 - Not starting - defect TPS54319 DC-DC converter U702 on main board

Baby TVs also can go kaputt. I got this little 22 inch sucker in a package together with a bigger one. It wouldn't start. A service manual was readily available at elektrotanya and I was looking forward to solving this case.

Just look at the little one! :-)

Standby voltage was ok. So I focused on the mainboard's DC-DC converters. They all measured ok. Was this probably a CPU or EEPROM problem? Hard to tell and not fixable for me.

I then remembered a YouTube video from the infamous EEVBlog, where Dave fiddled with a processor stuck in reset mode. So, just for fun, I located the reset pin at the CPU and put the multi-meter probe against it. The capacity of the meter was enough to pull the pin low for long enough to make the TV reboot. And lo and behold, something happened and the backlight turned on. Sometimes. Most of the time nothing worked. Once the set even booted fully, but didn't stay up long.

Suddenly, I heard a buzzing noise. The 3.3V provided by the main DC-DC converter chip U702 was wildly oscillating. It stopped freaking around when I pressed my finger on the chip, and the TV booted once I reset the CPU! So, this regulator did not provide a stable enough voltage during the boot process. Afterwards it looked as if everything was ok. Obscure failure that one.

Ok, I ordered 5 pieces of the TPS54319 chip from a seller on Aliexpress.com. Those QFN16 package chips are tiny and very difficult to solder. I fried the first one and it took three attempts until the thing sat aligned with the solder pads. Would you believe that this breadcrumb is capable of 3A output current? I find that quite astonishing.

The TV worked! It has a surprisingly good image, once the PC mode is selected and all the silly image enhancers are bypassed. Frau Johansson radiated into the room as good as it gets.

Philips 37PFL8694H/12 - picture solarized - another AS15F chip defect on TCON board

Have I already said that repairing AS15F chip defects is becoming a routine? This is my third repair of this type.

I like the higher Philips models. They usually have a nice image and proper sound. This one came in with a solarized picture, which seems to be the standard failure on 2008/2009 models. Some colors were off. Not as bad as the last one I fixed, but unmistakably, this was a defect AS15 chip on the TCON board. I have those chips on stock, so this was going to be some solder work with a very good chance of success.

Apart from the image defect, this set was in mint condition. Not one scratch.

The panel and TCON has been manufactured by AU Optronics (AUO).

Wires flopping in the breeze everywhere. Oh my.

First I was happy to see the TCON board not buried under the mounting bracket for the stand, but this was even more silly. The plastic frame, which goes all around the device covered it up:

Hidden screws :-(

With some screws removed and careful bending I managed to remove the cover to gain access to the gamma voltage test points. This would give me the final confirmation of the defect.

I was right. A couple of voltages were inconsistent. They must continuously increase from left to right. This board had a number of jumps in the voltages. No total failures, just half a volt off. This was consistent with the screen symptoms.

Ok, chip removed, solder pads cleaned. I prefer to use solder paste for the bottom pad. It makes the chip stick nicely to the board, and soldering the pins is easier. I first soldered the pins with the iron and then reflowed the whole chip with hot air.

This heat conducting block cannot be reused.

I had no 6mm material at hand, so I stacked a 1.5mm on a 5mm. I carefully had to position it under the cover because it would stick immediately and move out of its place.

TCON back in the TV. All good. Frau Johansson looked content, albeit a little tense, and I am happy about the successful repair.

This TV is a good one. I generally prefer the image of a CCFL panel over the LED types. The panel has no backlight bleeding and is perfectly even lit. The colors are natural and precise. There is a white balance adjustment available, albeit no expert mode. Sound is more powerful than average.

Philips 42pf9966 Plasma 2004 model - defect 100µ capacitor in standby power supply.

A little mouse can demobilize an elephant.

A friend presented a 2004 Philips plasma TV to me. The device would begin booting but once the relais clicked it switched itself off.

This is a BIG machine. Enormously heavy. The level of component integration just wasn't as high as today. Many boards with discrete circuits around. Even DC-DC converters, which come in chips today, were built with transistors.

It already has Ambilight - implemented with CCFL tubes, not with LEDs like modern models! Amazing.

It once cost 4500€ - not for very long though.

It had no stand and I didn't want to carry this monster into my lab, so I did some checks on it at my friend's place. Something had to be wrong with the power supply. It did not start all the voltages and switched off after 5sec or so.

I decided to pull out the supply for measuring in my lab. The excellent service manual was easy to find at elektrotanya. Wow, this is the biggest power supply I've ever seen!

I tried to figure out how to start it. In modern supplies this would be a simple connection to the power-good pin from STDBY or ground. Not here. This one produces three different standby voltages, which are partially looped through the main board and come back as OK-signals to the supply. It has multiple stages, which activate in a certain sequence controlled by individual signals.

I gave up on that and started to measure all the standby voltages instead. 3.3V, 5.2V were ok. But the supposed 9V were only 6.1V! I tracked down the smoothing cap. It was just a little 100µF SMD type.

I checked the voltage with my scope and the problem was clear: a 6V baseline and way too high spikes up to 9V. This cap wasn't doing its job. I removed it and it measured only 85µF. Dead alright! I soldered in a new one quickly and the voltage measured proper 9.5V.

Board back in the TV and it started just fine. Nice. As little as 1€ material bill this time.

This little sucker made all the difference in this enormously complex machine:

Philips used to be top of the notch. This plasma monster proves it. It is an engineering masterpiece, which flawlessly ran for over 10 years. These days Philips TVs don't stand out from the crowd. They are not even built by Philips anymore.

Samsung UE40C8790 - defect STD452S MOS-FET in Power Supply

I once had sworn not to test my luck on Samsungs anymore because you have to navigate the boards without proper service manuals. However, this set looked very interesting and its price was ok, too. A defect C-Series does not appear on eBay often. It seems to be generally reliable. On the other hand, there is a D-Series model listed almost every week and they usually have panel failures. Those are really bad. Don't buy a Samsung D!

This TV showed some reaction with its stand-by light, but wouldn't boot. It went click-click-click...

I have to hand it to Samsung, their higher models are looking pretty good:

It also has a fancier remote than the cheaper models.

Considering its young age - about 4y - I did not expect to find any dead capacitors. The seller said that it had intermittent problems and one day it wouldn't start anymore.

In this model Samsung went to extremes to design the device as flat as possible. It is not much thicker than my thumb! The chips on the mainboard use the back cover as cooler. Instead of the normal, large capacitors, they planted nests of tiny ones in parallel. That's not bad in terms of reliability, my only hope is that nobody will have to replace those. Not so easy to find.

The downside is that all connectors besides HDMI and USB need adapters. Even for the aerial antenna. That particular adapter was missing. The original Samsung part is ridiculously expensive. Some shops charge 35€!

Stereo? Who cares! Both speakers share the same cabinet:

A quick measuring of the voltages revealed a dead 12V line. It was dead short and a FET was the culprit. It's the little one in the center next to the coil:

A little weird how they botched the thing onto the board, right across two jumper wires.

An older version of the power board's schematic shows a different 8-pin type.

The solder joints looked terrible. The thing was already wobbling:

So here we have the reason for the intermittent failures. Cold solder joints. They cause instability and probably sparking, which eventually killed the FET. It is a very exotic part, a SamHop STD452S. The data sheet calls it STD4525. Anyway, there was none available on eBay for a reasonable price. I found a Chinese specialist called transistormosfet.com. 3$ a piece and another 8$ shipping. A fair offer. I ordered six pieces. This worked well. After 15 days they arrived as registered mail. I'll keep this shop in mind.

In a forum, people reported the same symptoms. This seems to be a standard failure.

So, what can be done to make the thermal situation of the FET more stable? It is obviously running too hot. First I used leaded solder, which is more elastic than lead-free. Then I decided to use a heat conducting block to attach the FET to the back cover.

First, two little splashes of nail lacquer showed me if and where it is making contact:

I carved out the plastic and did another lacquer check:

So that was looking good. I had the device running without cover and the FET surprisingly didn't run very hot. Anyway, this should prolong its life.

Frau Johansson was very happy with the results:

This TV has a very good picture. It is evenly lit, sharp, with brilliant and bright colors and good contrast. Like all the LED TVs a bit too aggressive in the reds and generally a little artificial for my taste - but I am a plasma man anyhow.

The sound is not bad either. A little inhomogenous, but powerful thanks to the closed resonance cabinet and both speakers working together.

So here we go, one part replaced this time.

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.