Hitachi 55HDT52 no picture, no audio

[Rack]

It's the same TV as in this thread (assuming Dennis H just kicked two letters around):
https://www.badcaps.net/forum/showthread.php?t=25765
with a different issue, though.

Service manual link:


After I opened up the back, I saw that the power LED wire was disconnected. After connecting that, I got a red light, solid. Upon turning it on, I got a solid green light, then it blinked 10 or 11 times, then a solid green light. The "Knight Rider" diagnostic on the main board was on "Flash Memory/Loading Program" when the power LED was blinking if I'm reading it right, then all the diagnostic LEDs turned off, indicating no error. I believe it was Tom66 that said in his videos "Thou shall check voltages" so that was I did.

Using the force voltage check procedure here:
http://www.justanswer.com/tv-repair/...l-55hdt52.html
I checked for standby voltages, and found them to be right near 5.5V and 3.3V. For the stage 1 check, I jumped the pins with a 1k ohm resistor, then checked various voltages. I got:
CNPPS:
24V: 22.0V
16V: 15.0V
10V: 10.7V
CNPPD:
5.6V: 5.7V
The (Vcc + 5.1V) pin read about 0.24V at this point.

The 24V and 16V look to be out of spec, but I jump some more pins for the stage 2 check anyway. I got:
CN64:
Va (~64V for this test): 0V
Vs (~64V for this test): 0V
Now (Vcc + 5.1V) pin is reading 5.1V, leaving Vcc right near 0V.

At this point, I'm stuck. I'm not sure if low 24V and 16V rails are enough to disable Va and Vs completely, and I'm not sure what would cause the 24V and 16V to sag so low in the first place.

[tom66]

Re: Hitachi 55HDT52 no picture, no audio

Va and Vs will drop if the Y-SUS or X-SUS is short on a plasma.
Unplug both Y-SUS and X-SUS and repeat the test for Vs (85V on Hitachi TERES-ALIS panel) and Va (55~70V for all plasma panels.)

[Rack]

Re: Hitachi 55HDT52 no picture, no audio

As part of the test procedure, both the Y-SUS and the X-SUS are disconnected before starting, I forgot to mention that.

[tom66]

Re: Hitachi 55HDT52 no picture, no audio

OK... Is there a pin marked VCEGO, VSEGO or VS-ON?

[Rack]

Re: Hitachi 55HDT52 no picture, no audio

VS-ON, not sure. I have a STBY2 and STBY3, which are jumpered to standby3.3V for the stage 1 power board test. I do have Vsago and Vcego which are jumpered to standby3.3V for stage 2 of the power board test.

[tom66]

Re: Hitachi 55HDT52 no picture, no audio

Ok, if VCEGO and VSAGO are high, Vs and Va should be there, but they aren't.
Did you check any fuses on the power board?

[Rack]

Re: Hitachi 55HDT52 no picture, no audio

I did check the fuses I found, they all had continuity. They were labeled F1AH, F2AH, and F5AH. I looked for possible F3 and F4 fuses, but I didn't see any.

[tom66]

Re: Hitachi 55HDT52 no picture, no audio

"1AH" "2AH" "5AH" probably indicate current ratings.
Can we have a picture of the PSU?

[Rack]

Re: Hitachi 55HDT52 no picture, no audio

Sure, but the pictures will be bad since all I have is an old iPod.
The heatsinks kind of get in the way of most of the caps on the topside of the board, but none of them look bulged in any way. Maybe I could get in closer with some more light if you wanted a closer look at something in particular.

[tom66]

Re: Hitachi 55HDT52 no picture, no audio

Do you ever hear a relay click when you turn the set on with jumpers applied?

[Rack]

Re: Hitachi 55HDT52 no picture, no audio

Yes, I do get a relay click when I turn the TV on with jumpers.
I was digging through the service manual some more, looking for more information.
Vcc is supposed to be +5.1V, it's a label, not a sum.
24V is supposed to read closer to 25V, 22V would be quite low.
16V is supposed to read closer to 16.5V, so 15V is pretty low as well.
10V is supposed to read closer to 10.5V, so 10.7V is okay.

[tom66]

Re: Hitachi 55HDT52 no picture, no audio

OK, do you see those two white resistors near the relay?

Sometimes they can fail open and cause lack of Vs/Va.

Can you check them for continuity?

[Rack]

Re: Hitachi 55HDT52 no picture, no audio

Sure! They are labeled as 10 ohms, they test at 10.3 ohm each (20.6 ohm in series).

[tom66]

Re: Hitachi 55HDT52 no picture, no audio

Hmm, OK. Are there any other feeds for Vs and Va going elsewhere in the set; for example, sometimes one goes to the buffers, or to Va goes to the panel directly.

[Rack]

Re: Hitachi 55HDT52 no picture, no audio

There just seems to be the one feed for Vs and Va coming from the CN64 connector on the power board, and for the Force Voltage test, the CN64 cable was disconnected.

[tom66]

Re: Hitachi 55HDT52 no picture, no audio

Can you check the output rectifier diodes on the PSU for Vs and Va?

If you need help post a picture of the bottom side of PSU, you may need to borrow a different camera.

[Rack]

Re: Hitachi 55HDT52 no picture, no audio

I'll have to work on finding a better camera, no one comes to mind at the moment.

Working back from the Vs pin, I see two diodes, D1529 and D1503. In diode testing mode, my meter reads 0.420V drop across both of them. The input of the diodes comes from pin 9 of the transformer T1502. The output of the diodes goes past a bank of capacitors, 4800uF in size, my meter read 4900µ in-circuit. At this point I wish I had an ESR meter, it'd be useful information to have. The output continues to a circuit that starts at my rectifier diode output after it passes the capacitor bank, let's call it junction A, goes through 3 3.3ohm power resistors in series, a IRFS634B drain (Q1512), the source connects to what I think is ground based on continuity. Junction A also connects directly to the Vs pin output on the power board.

Q1512 didn't seem to test like any of the other transistors using diode mode, but maybe it's special, I do not know. It wasn't shorted, though.
Spec sheet for the IRFS634B:
https://cdn.badcaps-static.com/pdfs/...62fa1479ff.pdf

Still working on tracing back Va.

[Dennis H]

Re: Hitachi 55HDT52 no picture, no audio

Yes, somehow I transposed the HDT to HTD in my thread, but we seem to have the same model accept my failure was no picture, but sound worked.

I initially had no Vs and Va, but after doing the check Rack linked to, I was able to verify that the power supply was indeed working (this was done with the Y sus disconnected.

I was then able to trace the problem further past the Ysus to the upper and lower buffer boards. With the Y sus in and connected but with both buffer boards removed, and the logic board reset out of protection mode, it will power up and give the correct Vs and Va at the CN31 plug pins on the Y sus. As soon as I plugged either buffer board in, it start to power up for a second (I could watch voltage rise to the rating) and it would then go into protect mode and Vs and Va would go to 0.

One thing I noticed, is you really have to be deliberate about making sure you have removed power for long enough to let the logic board reset from protection mode. It took me a while realize this.

Also, I noticed you mentioned the green light flashing at some point, Mine does that about 11 times when all the boards are plugged in at which point it goes into protect mode. When I have the buffer boards out, and power up, the green light just comes on like it should, ie it does not give the 11 blinks.

[Rack]

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.

[tom66]

Re: Hitachi 55HDT52 no picture, no audio

Here is how I test buffer ICs:
https://www.youtube.com/watch?v=51SZsfH60EY