Philips 42PFL9803 - chassis Q529 - two blinks - shot FDS8884 FETs on main board - typical fault

The Philips 8000/9000 series from around 2010 are my favorites after the Panasonic NeoPlasmas. This one came in with the two blink code. The seller said it suddenly switched itself off and never came back alive.

Just look at this. Two fans and four decent speakers. Only one adhesive tape, the rest is done with clips. The power supply is built for eternity. Back in those days, TVs used to have a protective shield in front of the panel and the frame was rock solid. The golden age of LCD TVs.

Ok, service manual readily available at elektrotanya.com. The Philips manuals from those days are enormously detailed. They even explain the DC/DC regulator circuitry. Real engineering pride. They always give me good confidence to attempt any repair, even on board level. First thing to do with a dead Philips is to activate the SDM (service default mode). This is done by shorting the SDM point on the main board to ground:

The device will ignore a number of checks and keep running. Also, it will morse an extended error code via the stand-by LED. In my case it was 1 long - 8 short, which means code 18. Let's look it up:

Aha, so next task was to locate the DC supply circuitry on the main (SSB) board and measure. I found a broken fuse:

I measured the FETs right next to it and found 7U05 to be dead short. It was the 1.2V DC supply. All the FETs are FDS8884. Didn't have those in stock, but I had a number of FDS8880, which are from the same family, but can handle more current. After removing the FET I also did an A-B check on the two identical PWM chips on the underside and found nothing alarming. So the PWM chip could still be ok.

Now, for testing I connected a fuse holder with a 4A fuse and started the device. Klack klack - dead - blinking. The fuse blew again! Was I a little to hasty this time?

The FET was shorted again. Why? Because I was sloppy and did not properly check 7U06, which wasn't dead short but almost. This so-called 'lower FET' goes to ground and 7U05 goes to 12V plus. Therefore, this sucker killed my new FET by pulling it to ground.

Now this got me thinking again: if 7U05 goes short, which is connected to 12V and is feeding directly into the 1.2V line, 12 volts are hitting the processor! Even for a short period of time, this could be fatal for main processor's core. I also did some research on the net and that did not lift my spirits, either. In a number of forums I found a couple of similar cases with no good ending.

With mixed feelings, I replaced both FETs this time. I connected the board to my bench supply, limiting the current to 500mA. I first connected the 1.2V line directly and it only pulled much less than that. Chances were high that the processor was still good.

Then I connected the 12V feed. The DC/DC regulator came up ok and the board pulled a constant current around 550mA. Nice.

Back in the TV, I still kept the 12V feed connected to the bench supply. The TV wouldn't come up unless I raised the current limit to 1600mA.

But that did the trick. It was working again! I was lucky. No ICs fried. A cheap repair.

Hallo Frau Johansson!

This TV confirmed my opinion about the 8/9er series. Brilliant image! Totally even backlight, crisp colors, very high contrast. Like all LCD TVs I've seen, it does not match the natural colors of a Panasonic NeoPlasma. The viewing angle is a little critical, too. The colors quickly wash out viewed slightly from the top. Like many LED LCDs, it emphasizes reds a little. The software does offer a custom white balance, which does help somewhat.

The sound is powerful, homogeneous and spacey, thanks to four proper wide-band speakers.

Epilogue

I was lucky++. Later I found the following warning note in the manual:

And this:

These guys know their stuff!

I should have checked the FETs first. In my case, the fuse blew and they were inactive, anyway. But if they had produced over-voltage without blowing the fuse, I definitely would have fried the main processor. The main board is not available anywhere, not even in the most exotic countries.
Always fully read the fucking manuals!

As this TV had some mileage, I also had a look at the power supply's solder joints. None of them showed any signs of aging. As a precaution I re-soldered all FETs and diodes. All heavy and hot parts are mounted in rivets, the heat sinks are ridiculously over-sized. They get a little more than hand-warm at best.

A great machine. However, it seems to have trouble with the DC/DC stage sometimes and according to some voices on the net, it may fry its processor.

So what about the three blinks error code?

The same model was on eBay at the time, with a three blink error code. According to the manual, this means 12V supply failure. Your first instinct would focus on the power supply. But, from what I know now, I'd suspect an identical failure, albeit with no open fuse. The DC/DC stage might produce heavy over-voltage and there is nothing the protection circuitry can do about it except cutting the 12V supply. The warnings from the manual have to be taken very seriously. The question is: did the ICs survive the attack or not?