Hitachi 55HDT52 no picture, no audio

[martyparish]

Re: Hitachi 55HDT52 no picture, no audio

I see you got your tripod Tom. looking good!

[tom66]

Re: Hitachi 55HDT52 no picture, no audio

Found at discount shop for 60p, and it works OK!

[Dennis H]

Re: Hitachi 55HDT52 no picture, no audio

There's a transistor, Q1515, that is connected to Vs at its drain, some other section at its gate, but from its source, it goes through a couple power resistors in parallel, to a little transformer, then past a capacitor on the way to Va. Nothing tests unusual.

I checked the other thread (Dennis H's) and saw that tom66 posted posted some troubleshooting guides, so I checked out the shorter one:
http://www.tgohome.com/ServiceManual...901_Dead_Tips_[TM].pdf
Testing ICs for shorts from Vcc to ground across capacitors between their voltage lines seems easy enough. First random IC on the upper buffer board, 5.9 kohm or so. Seems normal. Second one, 6 ohms. I tested some more and it seems about 50/50 at the moment; half good, half bad. Same story on the lower buffer.

Here's how I see the economic reality of the repair. One buffer board repair goes for like $85 on eBay, and "new" board is about $95 or so, which is probably just a pull from a cracked screen. My boards are already 6 years old at this point. The suspect chip is about $11 a pop from a TV repair shop domestically, or $4-$5 from China. There are 6 chips per buffer board. Given that they are 6 years old, I'm would lean toward replacing them all. Also, it is unknown how these shorted ICs damaged the Y-SUS board they are connected to, but I do see a combo repair of all three boards (2 buffers and Y-SUS) going for $210. Hopefully it's this condition that's causing the TV (power board) to kill the voltages to Vs and Va and not additional damage to the power board itself (looking not good since I couldn't get Vs and Va to come up even with jumpers).

Thanks for the key service manuals, tom66, but at this point, I'm not sure this TV is worth fixing. Maybe when I learn to pull the ICs myself it'll be more economical.

I decided to try the buffer chip repair and ordered the $11 chip. Just got it so hopefully this weekend I'll have a chance to replace it. I'll post back with results... hopefully good ones

Rack, I just noticed your in Cedar Lake, small world!

[Rack]

Re: Hitachi 55HDT52 no picture, no audio

Not that small of a world, still takes the better part of an hour and a half to get from me to you, Dennis H.!

I did most of my measurements with the boards still in the TV, but I took out the buffer boards and Y-SUS to give them a closer look, and see just what went wrong. From the picture, you can see one of the buffers got hot, but it seems only that one. Using the video tom66 posted, that was the only buffer chip with issues, but when I tested the buffer ICs while it was put together, every other chip was "bad". It wasn't actually the chips, it was how they are connected to the Y-SUS.

In this particular TV, the even buffer ICs get their power from one half of the Y-SUS board, and the odd ICs get their power from the other half. So when I was measuring 6 ohms, it wasn't the buffers, even though it indicated something was wrong. It was the Y-SUS that was connected to the buffers still.

Given that only half of the Y-SUS powers half of the ICs, and there are identical circuits for both halves, I can compare one against the other and see what's different. Given one side reads 6k ohms, and the other read 6 ohms, I'm going to go with the 6 ohm side being "bad" and start picking up legs of components until the short goes away. So far, tested the first cap I came to on the Y-SUS coming from the buffer boards. Not it, 47uF cap reads 48.0uF with one leg raised, and the board still reads 6 ohms.