LG42PQ60D PCB help needed please

[fnd45/4]

Hi,
This plasma TV belongs to my married daughter and son-in-law. It apparently just stopped working whilst watching it. Still had stand-by light and would give a click when they tried to turn it on again, but would not come on.
When I took on the task of having a look at it - I never like to throw anything out without first determining that it is beyond economical repair - it was not showing any stand/by light at all.
The PCB is a Model PSPU-J902A. PSPU-J903A Rev 1.2 2009.06.29.
LG IT PCB P/N : 3PAGC00001A-R
EAY60696801 (PSPU-J902A)
EAY60696901 (PSPU-J903A)




My first step was to check the fuses on the various boards. I found fuse F302 to have no continuity, and all others were okay.
I replaced this fuse and tested it with a DMM and all was good. I then reinstalled the PCB and left the connector plug to the YSUS board disconnected(YSUS is connected to ZSUS with a separate cable).
When I turned on the mains at the wall, there was a 'pop' from the TV and I turned in time to see a small spark arc out from the vicinity of the power board and a little puff of smoke, before I turned the AC off again.
After studying the board for a while and testing all of the fuses again, I was unable to find anything wrong. I then turned the power back on and waited for a minute or so, half expecting to start a fire, but nothing happened.
I have no stand-by light and the TV will not turn on. As the fuse I replaced and all others test okay, and I can find no visible signs of something having exploded (causing a spark), nor any scorch marks etc., I am stumped.
I have been thinking about purchasing a new PCB, but I am concerned that if I do so I might blow it up (the new PCB), if there is a fault elsewhere in the TV.
My questions therefore are:
a. Is my concern about blowing up the new PCB warranted?
b. Is there anything I can do to remove that risk?
c. Are there any simple checks I can do on this old board to see if it is
repairable?

Any expert advice will be very gratefully received.

Thank you

[fnd45/4]

Re: LG42PQ60D PCB help needed please

Sorry, but I can't find out how to / or whether it is possible, to edit my post, so I'll just add an update here.

I have now located a source of the spark and smoke that I mentioned.
IC301 has a hole blown in the front of it. This component is located on the centre heat sink at the bottom end.
It has the markings - "STR"
"W6252"
There was also a third line but this is just a hole with possibly "7P" as the last characters.

What I don't know now is whether this failure is a cause or a symptom of the initial problem and my subsequent replacement of the fuse (as previously mentioned).

Any assistance greatly appreciated.
Thank you.

[awyatt2]

Re: LG42PQ60D PCB help needed please

str-w6252 is a switch mode power supply driver, you need to check the components related to it to find out why it blew, probably has a shorted component somewhere. its a common part in icom smps.

[budm]

Re: LG42PQ60D PCB help needed please

It is all in one SMPS +POWER MOSFET for driving the power transformer for the standby power supply.
So look at the application circuit, it should be pretty close to what you have, so check the components in that section as suggested.

[fnd45/4]

Re: LG42PQ60D PCB help needed please

Thank you both for your replies. Thanks also for the attachment budm.
I'll attempt to do as you suggest.

[fzabkar]

Re: LG42PQ60D PCB help needed please

Here is a service manual:

[fnd45/4]

Re: LG42PQ60D PCB help needed please

Hi and thanks for taking the time to reply.
Unfortunately that link will not open for me, it just comes up "loading xxx kb /0.0 kb" and does nothing.

When I tried pasting it into Google, that came back with a story about robots.txt.

Any ideas please?

As an alternative thought, does that document provide the values of each of the components?

I would dearly like to know the values/specs of the following if you can help:

R305 and ZD303

Regards

Flin

[fzabkar]

Re: LG42PQ60D PCB help needed please

Try this:
http://www.jordansmanuals.com/Defaul...&Model=42PQ60D

[fnd45/4]

Re: LG42PQ60D PCB help needed please

Hello again,
Thanks for your help again.
It appears that I have some sort of settings issue with Acrobat Reader DC.
I am working on that at the moment.
I tried going straight to the Jordans Manuals web page and downloading it from there, but ran into the same issue.

I'll get there yet.

I'll let you know when I've managed to download it.

Regards
Flin

[fzabkar]

Re: LG42PQ60D PCB help needed please

The service manual has circuit diagrams for the main board, but appears to have nothing for the PSU PCB. :-(

[fnd45/4]

Re: LG42PQ60D PCB help needed please

Hi again,
Well I finally managed to download a copy of the Service Manual. I could not get Internet Explorer/Adobe Acrobat Reader DC to download it, so switched to Google Chrome, and had no problem. (I'll have to sort out why later).

I have spent a little while scanning through the S/M and then looking at the LG 42PQ20D, as it has parts lists available to download.

I had started to think that there had been a change in components along the way, as there was no mention (that I could find) in either of them that contained a Zener Diode. ZD303 is located on the PCB and is one of the components I can't find the specs for.
It looks more likely that you are correct, in that there is no PCB schematic diagram.
In the parts list for the LG 42PQ20, there is a part number (EAY60696801) for the PCB, (as follows):
Loc No..... Part No ..... Description(Local)..... Description(English) .....Specification

580..... EAY60696801..... SMPS,AC/DC .....SMPS,AC/DC ..... PSPU-J902A 100VTO240V 400W 50 TO 60Hz UL/CE/TUV - LG INNOTEK.,LTD.

That could be the listing for the complete board I suppose.

I guess it looks like a dead end.

I really appreciate your assistance so far.
If I may be so bold as to ask, can you provide any assistance with identifying a Zener Diode? ZD303 on this PCB is smaller than a grain of rice, pink/orange in colour and made of clear plastic or glass. It has a black band around one end, and has the letters D.C.I written around it - like this -

D.
C.
I

Any ideas?

Thank you sincerely.
Flin

[fzabkar]

Re: LG42PQ60D PCB help needed please

I would do some minor circuit tracing in that area. Then you could compare your circuit against similar implementations.

For example ...


https://cdn.badcaps-static.com/pdfs/...eeb8a910e3.pdf

[fnd45/4]

Re: LG42PQ60D PCB help needed please

Thanks, I'll do that.

Regards
Flin

[fnd45/4]

Re: LG42PQ60D PCB help needed please

Hi fzabkar,

I just wanted to send a final thanks for helping with my problem.

I have spent a lot more time searching for an approximate schematic, and looking online for LG's that use the same PCB - all to no avail.

I spoke to an LG parts supplier in Adelaide (no name, just in case it is not allowed), and have decided to order a complete board (refurbished).

Hopefully that will be the end of the problem - assuming there is nothing else wrong with the TV.

Regards and best wishes.