50pg20 maldischarge

[KevinCro]

I have been working on this tv for ages and I am not having much luck. I have replaced the smps and have purchased two ysus boards. I bought both ysus boards on eBay so I'm sure they all had the same problem. All the voltages coming out of the smps are correct. The only voltage that is off is the vy voltage. It's setting at -105 and should be -190 it will stay constant for a few seconds, then flash and go back to -105. None of the capacitors look bad although I haven't checked them with my esr meter yet. It's only letting me upload one pic at a time so I will post more after I transfer them from my iPhone to my computer.

[KevinCro]

Re: 50pg20 maldischarge

here are some pics of the boards

[Alastair E]

Re: 50pg20 maldischarge

Z-SUS board faultI would say--But check ALL the supply voltages, Vs, Va, VSC, -Vy, VZ-Bias first...

[KevinCro]

Re: 50pg20 maldischarge

I found a bad transformer on the Ysus. How do I identify the specs? None of the numbers seem to come up on google.

[tom66]

Re: 50pg20 maldischarge

How did you determine the transformer to be bad?
Note, SMPS transformers are very reliable and they very rarely fail!

[KevinCro]

Re: 50pg20 maldischarge

I replaced the zsus to no avail. Also, Turns out I was wrong about the transformer. I checked the vy voltage and it appears that if I place my probes on either side of the resistor, I get the proper voltage readings. But if I place one probe to a lead and the other to chassis ground the reading is poor and fluctuates. I'm not sure if that matters or not. I consulted the service manual and the readings that I get when testing the buffer boards are off. They all seem to be lower than what they should be. I'm in the process of buying new buffers so I'll update this when they come in. Anything I should check in the meantime? Thanks for the help.

[Hamie]

Re: 50pg20 maldischarge

Crazy throwing boards into a TV.
You have measured the correct way for -vy.
But what the vsc and zbais voltages?

You may have bought a faulty z-sus.

[KevinCro]

Re: 50pg20 maldischarge

I disconnected the zsus board and there were no changes to the operation of the TV. It would appear that I did indeed buy a bad part. I'll straighten that out and post results.

[KevinCro]

Re: 50pg20 maldischarge

New zsus from shopjimmy fixed the problem. Thanks for all the help.

[Hamie]

Re: 50pg20 maldischarge

Great news

[KevinCro]

Re: 50pg20 maldischarge

It seems that fixing one problem just reveals another. I've posted a pic of what the screen is doing.

[KevinCro]

Re: 50pg20 maldischarge

I had a similar issue with another set and it turned out to be the ysus. Thoughts?

[Alastair E]

Re: 50pg20 maldischarge

Not a Y-SUS fault. a y-sus/buffer issue will give horizontal lines, not vertical.

Summit to do with the vertical address (COF) chips, their data-lines, or the tabs to the glass of the panel.

Check where the tabs containing the COF Chips attach via ribbon-plugs to the boards that run along bottom edge of the panel, check all of the ribbons to those boards.

You'll have to remove the ally heatsink along bottom edge of the panel. Take great care, those COF are very delicate, easily torn/damaged, and do not run set without heatsink refitted.

You May get lucky, but in my experience, vertical lines on Plasmas usually ends up being one or more of the COF chips and is unrepairable.