Self-Inflicted Damage: Vizio P50HDM

[craigc15]

Aloha!
I am a TV guy from the 70's that obtained a EE degree. I've been involved in various pursuits, but now I'm back to fixing TV's!
I worked on a plasma TV last year and decided I would avoid them, but I ended up working on a Vizio P50HDM. I'll skip the original problem for now. I need to get back there first.

Problem: In my efforts to remedy the original problem, I was searching for "Bad Caps"! I replaced some of the big guys on the YSUS and ZSUS boards (the ones with slightly rippled tops), but that didn't change anything. I ended up removing/testing some of the caps on the PS board. Well, that's when the disaster struck. When I powered up the monitor (it's not a TV) all I had was what is shown in the attached picture.
When I looked over the PS, I noticed I had accidentally inserted 3 caps in the "5Vctrl" circuit backwards. Amazingly they didn't blow! I replaced them with new caps, inserted properly, but the problem remains. (The "5Vctrl" voltage is fine).
I have checked the following voltages:
Va = 60V, Vs = 196V, -Vy = -200V, Vsc = 115V, Vsetup = 115V, Z_Bias = 95V
I have also checked the IPM's according to this "Troubleshooting Manual": http://www.scribd.com/doc/16077007/L...07-VG-Training All is good, except a couple of the resistance readings were higher. I didn't think higher would cause a problem(?).
I looked at the YSUS output waveform with my o-scope and it looks like a square wave. It doesn't look like the one shown in the manual.

Then I created another problem. While re-installing the YSUS board I neglected to insert the screws that connect it to the Y-Buffer board! For those that don't know what happens when you do that, it arcs across the connections and wipes out Q1, R25, R26 on the YSUS board, and in my case it appears that it also wiped out something on the upper Y-Buffer board. The Vsc voltage dropped to about 85V with both Y-Buffer boards connected. When I disconnected both Y-Buffer boards, Vsc comes back close to 115V. I connect the lower Y-Buffer and Vsc is good, but when I connect the upper Y-Buffer, Vsc drops back down again.
I checked the FETS and diodes on the Y-Buffer board w/diode mode on my DVM, and all check fine. I did a magnifying glass inspection of the driver chips, and I don't see any burnouts.

Questions:

1) Is there anything else I can check and potentially replace on the Y-Buffer board, or should I just buy another one on eBay?

2) Any guidance on what might be causing what's shown in the picture? Maybe I clobbered both Y-Buffers by putting the caps in backwards?

Mahalo nui loa!

Craig

[freakaftr8]

Re: Self-Inflicted Damage: Vizio P50HDM

The picture on the screen is odd to say the least but I do t believe you will get an image unless you have a working upper buffer board.

[craigc15]

Re: Self-Inflicted Damage: Vizio P50HDM

Thanks for the fast reply.
The picture was taken before I (most recently) wiped out the upper Y-Buffer board.

[tom66]

Re: Self-Inflicted Damage: Vizio P50HDM

It is very typical for Y buffer failure.

http://blog.coppelltvrepair.com/2010...er-boards.html
http://blog.coppelltvrepair.com/2010...-lines-in.html

[craigc15]

Re: Self-Inflicted Damage: Vizio P50HDM

I am familiar with that info. I communicated with Bobby (Coppell) last week.
I have taken the measurements he suggests and everything checks fine, but given that having the Upper Y-Buffer connected loads down the Vsc, that's a strong indication that it's at least one of the driver chips.
Sounds like it's time to buy some Y-Buffer boards.
Any other suggestions welcome!

Mahalo!

[craigc15]

Re: Self-Inflicted Damage: Vizio P50HDM

I forgot to mention one more piece of info.
When I press the "Input" button, the vertical line strip widens and shifts to the left edge of the screen (where the input info normally appears).

Does this still sound like a Y-buffer problem?

Mahalo!

[freakaftr8]

Re: Self-Inflicted Damage: Vizio P50HDM

That's a ysus problem.