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.