HCT HPP-42HCB Plasma video issues, audio working

[kisk]

I run a computer repair shop and have recently started working on TVs, however I do not have a whole lot of experience past very general diagnostics, so I would love to learn! I have good soldering skills and even do chip reballs in my shop. Have my DMM in hand and was hoping you guys would help me diagnose this plasma. Can't find a service manual on this model either. Here's the info:

Client brought in this plasma. Audio works but the picture is near black (backlights still work). There is very faint and spread out colored snow and ever once in awhile you can see a faint white snow come over the screen in sort of a cloud-like pattern. You can also sometimes see the OSD very faintly. I have checked and adjusted the Vs (186v) and Va (60v) voltages using the corresponding potentiometers just to make sure they were where they needed to be. Vs was about 10v off and Va was about 7v off.

Pulled out 5 fuses and all tested ok.

Being a video issue where the audio was still working, I thought it would most likely be the logic board, which I have swapped, but there is no change in symptoms. I will post a video of the snow and pictures of the boards. Any ideas where to start? Could it simply be the panel? Thanks for the help!

EDIT: Pics posted. Btw, all caps look fine -- no bulging or leaking found.

[Ijaz Ahmed]

Re: HCT HPP-42HCB Plasma video issues, audio working

The symptoms you have described are related to Z-Sus board. So focus on Z-Sus, haqve you checked the SMT fuses on Z-Sus (near P1 connector, Red and Blue wires) ?

You should check for open or shorts on the power semiconductors, power resistors etc. What is the exact part number of Z-Sus board ?

[kisk]

Re: HCT HPP-42HCB Plasma video issues, audio working

Thanks for the reply.

The Z-Sus board is 6871QZH056B. Fuses check out and I didn't find anything out of the ordinary anywhere else. Any particular test points I should check out? Here's a few closeups of the board.

[kisk]

Re: HCT HPP-42HCB Plasma video issues, audio working

Ok found an open 470k resistor (R22) on the daughter board. I would assume this could be significant? Never seen this before, but the lower end of the resistor connection is either rusty looking or has some sort of coating on it. Is this normal?

[Ijaz Ahmed]

Re: HCT HPP-42HCB Plasma video issues, audio working

Nice find, the daughter board seems to be a switcher at local level and this R22 looks like in the primary side and in the snubber circuit for Q20. You should also check Q20 and if found bad, also suspect the U20 (seems a PWM controller) and the D20 as well.

[kisk]

Re: HCT HPP-42HCB Plasma video issues, audio working

Well back to square one. My multimeter (cheap $5 china model) seemed to be acting up and I wasn't trusting it so I went to Harbor Freight and bought a Cen-Tech P98674 and now I'm getting the correct readings on that resistor and its surrounding components.

I did find a "repair kit" for this board for $35 but I can get a used board for $45. Any other ideas on component testing before I decide to just buy a replacement board?

[tom66]

Re: HCT HPP-42HCB Plasma video issues, audio working

Panel manual.


search 42X3 (I think it's a PDP42X3?)
It indicates where to check -Vy, Vsc and Vzbias to see if those modules are OK.

[kisk]

Re: HCT HPP-42HCB Plasma video issues, audio working

Excellent! This will help out tremendously. Will update after I've ran through everything.

[kisk]

Re: HCT HPP-42HCB Plasma video issues, audio working

Well all adjustments are right on par (Vs, Va, Vy, VSC), and all wire connections to other boards are at spec as well. Unable to test the Y-drive waveform as I don't have the proper tools.

A few things I did notice:

After about 1min of operation, there is colored snow where the OSD would be displaying "no signal". Its a very concentrated mix of rgb snow.

After about 5min of operation, the Y-Sus heatsink is still cold. The Z-Sus is warm.

On the Y-Sus board, there is a robotic sound coming from either the daughter board or possibly the fat orange capacitor (C51 in the bottom right of pic -- this was the VSC test point). I've attached an audio clip of the sound (ff to 20seconds). Is this sound normal? How about the Y-Sus heatsink being cold and the colored snow?