Hitachi P50H401A fixed but flashes of black

[Videojoe]

Well this is the third one of these I have fixed by doing exactly what I read here. Replaced the two 3300uF, 100v caps on the power supply and the lower y scan buffer. Cradeal.com has always given me quality y scan boards for about $62. So it fired up beautiful, done deal. I put the many,many screws back in an buttoned it up. But this time I noticed that when you turn it on, it flashes to black screen for a couple seconds and beautiful picture returns. It does this every now and then after that. Whenever you change the channel it goes black for a second and comes back. If you switch to an standard def channel, it makes an appreciable glitch and comes back to normal. Is this sync loss? Blanking? Anyone know where to adjust this? I don't have an o-scope, just a fluke multimeter.

[Videojoe]

Re: Hitachi P50H401A fixed but flashes of black

Can anyone help me out with this?

[Videojoe]

Re: Hitachi P50H401A fixed but flashes of black

Vs=87.7, Va=65.2v matching sticker on panel.

[tom66]

Re: Hitachi P50H401A fixed but flashes of black

Do Vs or Va drop out when panel blanks?
Does panel glow go away when it blanks?

[Videojoe]

Re: Hitachi P50H401A fixed but flashes of black

I just measured Va and Vs and waited for the screen to blank again and yes, both voltages drop out completely to 0 for a second or two until the video comes back on. I do believe the glow disappears also. I guess with no voltages present, the glow would disappear. What does this tell us Tom?

[tom66]

Re: Hitachi P50H401A fixed but flashes of black

Check VSAGO and VCEGO on power board. Do these drop out too? If not, then the power board or sustains are causing the drop out.

[Videojoe]

Re: Hitachi P50H401A fixed but flashes of black

Well now as I was measuring those voltages at the connector on the power supply, I noticed there were two screws missing that not only hold the board to the chassis, but supply ground to that section. I assumed all the grounds were tied together. So I put in the screws and now the tv stays on with no dropouts at all. I've been watching it for a few days now and everything is good. I'm gonna put this one in the win column, thanks for leading me to the problem.

[R_J]

Re: Hitachi P50H401A fixed but flashes of black

I assumed ....all the grounds were tied together
^^^^ There's that word

[Videojoe]

Re: Hitachi P50H401A fixed but flashes of black

dammit, its doing it again. Screen blanks to black randomly for a few seconds.

Vs goes from 87.7 to 0v
Va goes from 65 to 0v

Vsago goes from 2.7V to 0
Vcego stays steady at 3V

Logic board problem you think?

[tom66]

Re: Hitachi P50H401A fixed but flashes of black

No anomalies on picture when before vs drops out?

[Videojoe]

Re: Hitachi P50H401A fixed but flashes of black

Nope. its perfect when it cuts out and perfect when it comes back. Audio is undisturbed.

[ajshoe]

Re: Hitachi P50H401A fixed but flashes of black

did u find solution ?? I've noticed that all the screws in the YSUS must be in and tight or this happens. Have a P50H401 that did this.

[Videojoe]

Re: Hitachi P50H401A fixed but flashes of black

Yes the center screw was missing from the X sus board and another one was loose. But youre right, the y sus board will cause the same thing if its not tightened.

[Shane711]

Re: Hitachi P50H401A fixed but flashes of black

I just got done working on a Hitachi P50H401A. The 2 3300 Caps were swollen but I did not have any replacements so I tried to make one by sticking a bunch together to make the two 3300's but that did not seem to work. So I just ordered two new caps and I have to see what happens when it comes in.

Right now the TV turns on but shuts off in about 3 seconds. I removed both buffer boards one at a time and it didn't make a difference. I am assuming my Power Board is still having an issue. I thought putting the caps together would work but I guess I am wrong. If the two new caps work then that will prove I was wrong.

I took a picture of what I did, looked good to me.

[Shane711]

Re: Hitachi P50H401A fixed but flashes of black

Correction. I was just messing with the TV and there is a fan that cools the power board. It was not spinning. I took it off, cleaned it and tested it. Put it back on and now the TV is working. I guess my Cap Pack worked after all. Now I have to buff the screen because it has that coating pealing off. I found buffing it with some liquid buffing compound does a great job.

[kca]

Re: Hitachi P50H401A fixed but flashes of black

I've been working on a Hitachi P50H401 for a couple of weeks now, learning from this site and other forums as well as I have progressed. I'd really like to get some quality, detailed advice before I plug back in new SDR boards to help ensure that I won't lose them when power is applied.

Here is my current scenario:

1) The two 3300uf caps were swollen, so I replaced them both.
2) The two SDR boards (U and D) were both clearly damaged.
3) I disconnected both SDR's and connected a video source. It now goes from red to solid blue on the front panel and stays that way. The sound is perfectly fine, but there is (of course) no picture as the SDR's are unconnected to the YSUS board.
4) I can change channels (as evidenced by the sound of various channels changing) with the DirecTV remote and can change the volume with the Hitachi remote.

I have checked, double, and triple-checked all of the voltages involved.
PSU is fine.
PSU to XSUS is fine (via connector CN23)
XSUS to YSUS is fine (via connector CN22)
YSUS from XSUS is fine (via connector CN32)


My focus is now on the YSUS Board (and, in particular, the two connectors that lead out from the left side to the SDR's):

THIS is the current crux of the matter. I tested all 25 pins on the lower left connector that comes out of the YSUS board (and ultimately leads into the SDR-D), and ALSO the 25 pins on the YSUS upper left connector (that leads, ultimately, to the SDR-U).

I assumed that I would find exact voltage matches because both of these connectors are labeled exactly the same on the circuit board itself. That turned out to be the case, the voltages do match, EXCEPT for pin #8 and pin #21 (counting up from the bottom) on the LOWER LEFT CONNECTOR ONLY. Those two read 0.00

All of the upper left connector pins had readable voltages, including its pin #8 (-24.5v) and pin #21 (-51.8).
Note: This pin #8 is labeled as DA2 on the circuit board, and pin #21 is labeled as DA1.


All of this leads to a rather simple question I hope can be answered. Does the fact that I get the two 0.00 readings on the lower left connector mean that this particular YSUS board is entirely defective and must be replaced?

{Or, can I repair it in some way? Or, as is my hope, will these two 0.00 readings NOT prevent the SDR-D board, or the tv in general, from working properly when I connect it?}

It seems very odd to me that the upper left YSUS connector has readings at pins #8 and #21 and the lower left YSUS one does not.

Please feel free to reply in as detailed and as exacting manner as you'd like. I am into this pretty deep, as you can see, and I want to get it right before risking $120+ on the SDR U and D's.

Thanks in advance for your replies.