LG RU-42PX10C -- Bad ZSUS board

[ben7]

Hey,
Just got a trash-picked tv to repair. As the title says, it's an LG RU-42PX10C plasma TV. Date of manufacture is november 2004.

Plugged it in and I got no signs of life from the set. (had a sign on it saying "broken")

The ZSUS board model is 42V6.
FS1 (T4.0AH 250v) is bad. There is also a short from the 5v pin on P1 to ground - I am assuming that is why the TV didn't show signs of life. The 5v pin on P1 is connected to FS3 (10A 125v), however it isn't blown.

Is there a possibility that something else in the tv has gone pop? I unplugged the ZSUS board and turned the TV on, and it came on - power supply clicked, but I couldn't see the power indicator light since the tv is resting on its front side.

Pics soon!

Thanks,
-Ben

[ben7]

Re: LG RU-42PX10C -- Bad ZSUS board

Here are some pictures.

The two capacitors on the YSUS look bulged but it seems that it is just the plastic disc which has warped...

Oh, and FS1 is 2A fuse, not 4A

[tom66]

Re: LG RU-42PX10C -- Bad ZSUS board

Replace the fuse... common failure on these boards. Often the IPM is OK. Don't expect much from these. Just 480p really old plasmas.

I'd be surprised if there is a 5V short. There is a lot of capacitance on that rail (like 15,000uF from memory) so it could just be taking a long time to charge up.

[ben7]

Re: LG RU-42PX10C -- Bad ZSUS board

I'd be surprised if there is a 5V short. There is a lot of capacitance on that rail (like 15,000uF from memory) so it could just be taking a long time to charge up.

I measured it with the board out of the tv...

[tom66]

Re: LG RU-42PX10C -- Bad ZSUS board

I don't think the IPMs use 5V, so look for the logic buffers, MLCC ceramics. Of course I could be wrong, if these are older IPMs, they may use 5V and that may be short. Normally they use 15V for FET drive. Could be using both.

[ben7]

Re: LG RU-42PX10C -- Bad ZSUS board

I don't think the IPMs use 5V, so look for the logic buffers, MLCC ceramics. Of course I could be wrong, if these are older IPMs, they may use 5V and that may be short. Normally they use 15V for FET drive. Could be using both.

The pins of the IPM are marked, underneath the board. There is one that is marked 5v lol. Didn't measure to see if that pin is connected to the 5v pin yet, I will do it tomorrow.

[ben7]

Re: LG RU-42PX10C -- Bad ZSUS board

Update.

So I replaced the fuse FS1 with a 2 amp fuse. Powered on, and it didn't blow ... Vs and Va don't come up.

[tom66]

Re: LG RU-42PX10C -- Bad ZSUS board

The IPM is dead, Jim.

[ben7]

Re: LG RU-42PX10C -- Bad ZSUS board

The IPM is dead, Jim.

Could it have popped stuff on the other boards too? I just want to know before I look for a replacement zsus board.

[ben7]

Re: LG RU-42PX10C -- Bad ZSUS board

Looked at around 3 dozen sites, they were all out of stock LOL.
BUT, I found this. Would that be the right board? It looks exactly like mine! Not too bad a price, other sites (which were sold out) had it for over 100 bucks...

[tom66]

Re: LG RU-42PX10C -- Bad ZSUS board

Is it worth it? It's only a 480p plasma TV. Not HD capable. You'd be lucky to get $60 for it.

[ben7]

Re: LG RU-42PX10C -- Bad ZSUS board

Is it worth it? It's only a 480p plasma TV. Not HD capable. You'd be lucky to get $60 for it.

I'm not really looking to sell it.

Anyways, I desoldered one side of the IPM and saw that it was indeed toasted. I basically used more force to get the other side off, but I don't care if it is not worth fixing.

Pics:

Overview:


Closeup of fried transistors:


I can't understand why they wouldn't use current balancing resistors for the transistors, that is likely why they failed. One probably conducted too much current, shorted, and popped the other one, and the fuse too.