Zenith Plasma Z42PJ240 sound but no picture

[Bamakc]

I have a Zenith/LG model Z42PJ240 that has sound but no picture. The screen is very dim in a dark room. I have 205.5 vdc on VS and 60.4 vdc on VA. The only thing that i can find is 2 shorted transistors on the Z sustain board. Q206 is shorted between all legs and Q203 is shorted between ey316 and ey317. This test is with both transistors removed from the board. I am an old CRT type repair tech and have not worked on tv's for several years. I was given this tv by a friend that knew i liked to tinker with electronics and i am excited about getting back into this as a hobby only. Any info or guidence would be greatly appreciated.
Thanks,
Keith

[Bamakc]

Re: Zenith Plasma Z42PJ240 sound but no picture

Did i make someone mad or something??? I was hoping someone would tell me if i am on the right track or not. If i replace the Zsus board will this fix my problem? I do have sound and the screen glows in a dark room.

[tom66]

Re: Zenith Plasma Z42PJ240 sound but no picture

We are volunteers, time limited. We'll skip over threads which don't have the right information or sometimes we'll just miss them by accident.

Post some pictures of the chassis so we know what we are working with.

It is likely a Z-sustain fault.

[Bamakc]

Re: Zenith Plasma Z42PJ240 sound but no picture

I replaced the Z sustain board with one that is supposed to be new that i bought off ebay and the screen comes on bright and white for about 3 seconds then goes back off but sound stays on. I have also attached some pics.

[Bamakc]

Re: Zenith Plasma Z42PJ240 sound but no picture

Here is a few more pics. Any info will be greatly appreciated.

[Bamakc]

Re: Zenith Plasma Z42PJ240 sound but no picture

Does the blinking led on the board below the power supply spell out some kind of error code???

[tom66]

Re: Zenith Plasma Z42PJ240 sound but no picture

The blinking LED indicates a functioning control board.
What is the panel model in this TV? It will be indicated on the LG model sticker. e.g. PDP50R4000.

[Bamakc]

Re: Zenith Plasma Z42PJ240 sound but no picture

Pdp42t1001

[tom66]

Re: Zenith Plasma Z42PJ240 sound but no picture

I have an alignments guide; it has some test points.
http://www.tgohome.com/ServiceManual...&Search=Submit

I may have some more manuals in a few days time when a disk arrives from a friend.

Does the screen go bright then dark repeatedly, or does it only do it once? Did it work for 3 seconds then die?

[Bamakc]

Re: Zenith Plasma Z42PJ240 sound but no picture

The screen goes white for about 3 seconds the dark with sound. I unplugged it after about 10 more seconds... i didn't want to risk damaging the new ZSus board that i just put in.

[tom66]

Re: Zenith Plasma Z42PJ240 sound but no picture

Test the Y-sus and new Z-sus for shorts.

It may be that you need to adjust the Vzbias, Vsc, etc. But you can only do them with the set fully connected and powered up. It's a shame that the chained design makes this potentially hazardous to the new boards.

[Bamakc]

Re: Zenith Plasma Z42PJ240 sound but no picture

Thanks Tom... i downloaded the alignment guide that you posted and will go through the adjustments but will test the Y-sus and Z-sus first. I will post my findings.

[Bamakc]

Re: Zenith Plasma Z42PJ240 sound but no picture

I have followed the alignment procecures except the ones requiring a o-scope.
All of the voltages were within range but i tweaked them to make them exact.
I could not find a short on the Y-sus or Z=sus. All voltages are correct on the power supply. When first turned on the picture is all white for about 3 seconds then i hear a click (like a relay) then the picture goes black but i still have audio. In a dark room the screen does not have a glow like before i changed the Z-sus.

[tom66]

Re: Zenith Plasma Z42PJ240 sound but no picture

OK, in the middle of the set you have a small green board connecting a lot of the boards together, this is the control board.

On it, there is a jumper space marked EXT AUTO GEN.

Take a 100 to 470 ohm resistor (any value from 100 to 470 ohm is fine) and place it across the EXT AUTO GEN pads.

Disconnect the LVDS cable -- runs between main board (has HDMI ports on it) and control board -- then turn the set on.

Do you get test patterns, and do they last?

[Bamakc]

Re: Zenith Plasma Z42PJ240 sound but no picture

I put 2 80 ohm resistors in series and I have no video at all. I disconnected the cable going to the main board before I do this .

[tom66]

Re: Zenith Plasma Z42PJ240 sound but no picture

This indicates you either have a control board, buffer board or Y-sustain defect. Testing the Y-sustain will require an oscilloscope and 10X probe. Do you have one of these?

[Bamakc]

Re: Zenith Plasma Z42PJ240 sound but no pictures

No I don't have one or access to one

[tom66]

Re: Zenith Plasma Z42PJ240 sound but no picture

Shame, this will be difficult. Plasma repair without scope is difficult for tricky problems like this. These newer plasma TVs used combined ERC which means that a failure on the Z-sustain can easily kill the Y-sustain.

One other thing to check. In this photo there's a small thin four wire cable coming off the Y-sustain and going into the X driver board along the bottom of the panel: https://www.badcaps.net/forum/attach...9&d=1368157361

What do you measure between the two outer pins? It should match Va.

[Bamakc]

Re: Zenith Plasma Z42PJ240 sound but no picture

It is 60 VDC which is VA

[Bamakc]

Re: Zenith Plasma Z42PJ240 sound but no picture

I no longer have the white display when I apply power