LG PDP42G1 panel help

[zedexnz]

Newbie to this and have been doing alot of reading.

Have the above named PDP42G1 panel which is not showing any picture.

Check the Va and VS and they are correct from the power supply board.
When the unit starts up the YSUS and ZSUS boards sound like they are "priming" as in they humm, quiet loudly actaully.

Nothing on the screen and nothing when shining a light on it. ZSUS is feed from the YSUS board.

Checked the VSETUP/-VG as labelled on the board and it looks as if there is something wrong there, but i dont know what the expected values are:

On the panel it has:

-187/140/NA/100

but im not sure which values correspond to which. My readings are:

VZ=81v
VSC=2.1v
-VG=nothing

Should I be looking at the YSUS board or maybe the controller board not giving the signals to prime the YSUS --> ZSUS up properly??

Any help appreciated.

Thanks

TEX

[rayrod81]

Re: LG PDP42G1 panel help

Vz is a little low but that would not cause the problem. I am assuming -Vg is supposed to be -187V and Vsc is 140V. The fact that they are reading so low leads me to believe that there is a problem on the Y-sustain or shorted buffers.

[zedexnz]

Re: LG PDP42G1 panel help

Thank for the confirmation Ray.

I disconnected the ZSUS for testing, just in case it was something down line that was drawing current.

All the main transistors test fine and there is no visual issues with the buffers I can see. What area of the YSUS should I be looking at next?? For the guys who do component level repair to the YSUS boards, what normally fails?

Thanks, its be a greta learning experience.

[rayrod81]

Re: LG PDP42G1 panel help

On any Y-sustain it is usually mosfets and diodes that fail. Pictures of the boards would help without them there is nothing more I can suggest.

[zedexnz]

Re: LG PDP42G1 panel help

I have attached a pic of the board. I have checked the FETS and they all seem to be fine after comparing same FET and thier readings.

Checked the most obvious diodes, but many cannot be accessed unless the heatsinks come off.

[rayrod81]

Re: LG PDP42G1 panel help

Yeah it is possible and very likely that there may be shorted FETs under those heatsinks. It would be necessary to take them off and test the components underneath.

[zedexnz]

Re: LG PDP42G1 panel help

So i pulled some of the FETs off to test independant of the board. Found that i have two 45F122 which give different readings. Now is there a special way to test these FETS??? Should I be expecting a single junction only?

[reinforce]

Re: LG PDP42G1 panel help

I have the same panel PDP42G1 with no picture. Sound is ok.
Upon checking on YSUS board, VZ=80V, VSC=139V and -VY=186V
2 questions for the experts: I don't find -VG measuring point and I should expect -VY to be -186V instead of the measured 186V ?
Thank you in advance

[tom66]

Re: LG PDP42G1 panel help

A quite loud humming can indicate the panel has cracked...

[tw2005]

Re: LG PDP42G1 panel help

So i pulled some of the FETs off to test independant of the board. Found that i have two 45F122 which give different readings. Now is there a special way to test these FETS??? Should I be expecting a single junction only?

It's an IGBT if that helps. Toshiba GT45F122

This video helped me test my 45G128 http://www.youtube.com/watch?v=AfV7gYChILc

[reinforce]

Re: LG PDP42G1 panel help

Thank you for the feedback. Appreciate so much your manual link http://www.tgohome.com/ServiceManuals . Thank you, Tom66
From the manual, I understand that the -VY voltage reads positive instead of negative.
However, VZ voltage measured only 80V instead of 100V as stated on the Panel.
Anyone can clarify if this is faulty and results to no screen & picture?

[reinforce]

Re: LG PDP42G1 panel help

Failure found and fixed. TV is running since then.

[tom66]

Re: LG PDP42G1 panel help

Can you tell us what the failure was, for future reference?

[reinforce]

Re: LG PDP42G1 panel help

Can you tell us what the failure was, for future reference?

Yes, tom.

The failure was on the controller board. IC201 was not driving YSUS board properly, hence the voltage drop on VZ which was measured at about 80V. Factory value is 100V !

On the top right of the controller board, there are some status LEDs. If
the board is working, at least LED D103 should light up.

Hope this helps...
Regards
rein

[tom66]

Re: LG PDP42G1 panel help

Thanks! Unusual fault, though! Will keep this in mind. We've had a few control boards fail that make it look like Y-sus etc are faulty.

[Tony2k]

Re: LG PDP42G1 panel help

Yes, tom.

The failure was on the controller board. IC201 was not driving YSUS board properly, hence the voltage drop on VZ which was measured at about 80V. Factory value is 100V !

On the top right of the controller board, there are some status LEDs. If
the board is working, at least LED D103 should light up.

Hope this helps...
Regards
rein

Hi Rein! I have exactly the same problem: no picture and LED D103 off. I'm not able to find IC201, can you explain me where I have to look?

[tom66]

Re: LG PDP42G1 panel help

My guess would be IC201 is on the control board and is a buffer IC of some kind, likely 14 pins TSSOP package or similar, I have since seen a few of these go bad on Samsung and LGE PDPs.

[Tony2k]

Re: LG PDP42G1 panel help

But this IC is on the YSUS board or on the logic control board?

[tom66]

Re: LG PDP42G1 panel help

The post above says control board, but these types of ICs are found in both places.

[Tony2k]

Re: LG PDP42G1 panel help

I'm in the same situation of Reinforce and I don't understand if I have to replace the YSUS board or on the logic control board...