LG 50PJ350 dead, relay clicking

[zape]

Re: LG 50PJ350 dead, relay clicking

Yes that's exactly what I experienced with the replacement board,
The same FETs are blown. The buffer board is not shorted, so I'm a bit confused. Could this be something else, like panel?
I did find a schematic of a similar Y-SUS board if that helps
see attached

[Keshenatech1]

Re: LG 50PJ350 dead, relay clicking

This sounds very similar to one I'm trying to figure out. Had 7 blown dead shorted mosfets in Ysus board, replaced, and it blew out again on power up. I didn't see any shorts on the driver IC's and nothing obviously shorted on Z board or buffer board, but I'm suspecting the buffer boards anyway because that's what the Ysus board drives. Just wondering if you ever had any luck with yours and what the problem turned out to be? Maybe similar issue in mine could point me in the right direction. Thanks

[zape]

Re: LG 50PJ350 dead, relay clicking

Bought another Y-SUS board and have the same symptoms, not sure if the board was working tho

[zape]

Re: LG 50PJ350 dead, relay clicking

I do have a scope, but no isolation transformer, so I will only be able to measure against ground and it looks like in Y-SUS they have some sort of isolated drivers.
I did double check the other IGBTs (I ordered more than I needed) and they look good.
I also noticed that when I power the TV on the Vs surges over 212v for a moment and then goes back to spec 206v. Not sure if this is normal.

[R_J]

Re: LG 50PJ350 dead, relay clicking

Do you have a scope to check the drive waveforms? They could be fake igbt's but the fakes usually short and go BANG!.

[zape]

Re: LG 50PJ350 dead, relay clicking

Verified. all looks good.
I wonder if this could be fake IGBTs from china
I purchased on ebay. though I quickly tested them with multimeter - by measuring Vce drop before and after touching the gate with positive lead

[R_J]

Re: LG 50PJ350 dead, relay clicking

You should be able to check ic703, it has 1 PNP and 1 NPN transistor. You might be able to check the IRS21850S, check that there are no shorts between VS~HO and VB~HO

[zape]

Re: LG 50PJ350 dead, relay clicking

Bad IGBTs were Q22, Q24 and on of the Q02, Q03
R709/10 and R711/12 and R730/31 and R372/33 - all good

IRS21850S is connected to the gates of the Q02/Q03
ADUM1234BRWZ is connected to the gates of Q22/Q24 via the small IC703

here is the photo:

[R_J]

Re: LG 50PJ350 dead, relay clicking

It could be ic703? I don't know which igbt's you replaced because I only have a SJ picture to go by. You likely need to clean the surface of the ic (could be dual transistor) with alcohol to read the number. It could be marked 5K (HN4B101)
Are the gate resistors on the bad igbt's, R709/10 and R711/12?

[zape]

Re: LG 50PJ350 dead, relay clicking

The gate resistors are OK
Any hints on which driver IC to replace?
I see there is a ADUM1234BRWZ chip but it is not directly connected to gates, but thought some small 5-pin IC with no identification marks (IC703).

Also there are 3 smaller 8-pin ICs marked 34H 037 (could not identify it or find any datasheet)
and 8-pin ic IRS21850S

[R_J]

Re: LG 50PJ350 dead, relay clicking

If the transistors were shorted drain or source to the gate, it is a good chance the gate driver IC is damaged or at a minimum gate resistors. In that case the new transistors are not even being driven.

[zape]

Re: LG 50PJ350 dead, relay clicking

replaced the transistors on the Y-SUS board and now I see different symptoms:
any idea what this could be?
https://photos.app.goo.gl/cgFEzQ5YE5vqzmdv9

Relay is no longer clicking but Vy/Vsc and Vzb voltages are out of spec.
Vy/Vsc are very low - starting from high and quickly go down to 20v 1v respectively, Vzb starts high and then goes down to ~55v instead of 95
I also noticed the led on the T-CON blinks with some pattern, I wonder if there is any code that may indicate the cause of the fault?

[zape]

Re: LG 50PJ350 dead, relay clicking

I have similar symptoms and identified three bad IGBT transistors on Y-sus board:
- two RJP63F3 - Q22, Q24
- one 30F124 (the other 30F124 survived but I will replace it regardless) - Q02, Q03

Should I look for better alternatives? e.g. higher voltage or lower Vce replacement? Someone mentioned here that he replaced 30F124 with 30J124 https://www.badcaps.net/forum/showthread.php?t=68790
Anything else I should check before I order parts?

[Alastair E]

Re: LG 50PJ350 dead, relay clicking

Driver chips or transistors faulty causing new 63f4a to short...

[alltvrepairs]

Re: LG 50PJ350 dead, relay clicking

Hello,
I know this is an old thread.

But is it possible to try the YSUS with Buffer boards and ZSUS completely removed?
Or the YSUS will get damaged ?

I am asking as have replaced already the faulty RJP63F3 IGBTs and blew immediately after switching on with Buffer boards and ZSUS removed from place.

[aasnowskate]

Re: LG 50PJ350 dead, relay clicking

I received the new YSUS and ZSUS today. I put both new boards in and it worked again! I am afraid to put the old YSUS back in as it might blow the ZSUS. Could this happen?

[tw2005]

Re: LG 50PJ350 dead, relay clicking

I guess I will have to buy another y board to be safe along with the x board.

The zenith got going again with ysus,zsus swap after he blew his first new ysus. He put his original zsus back in and confirmed faulty.

I would not recommend putting the old zsus back in if you do get this going , not worth the risk of possibly blowing the ysus

Looks like he may have a panel fault too.

[aasnowskate]

Re: LG 50PJ350 dead, relay clicking

I guess I will have to buy another y board to be safe along with the x board.

[tw2005]

Re: LG 50PJ350 dead, relay clicking

So it must have been more than just a ysus. it's tough but that's why I replaced x,y and buffers on the Samsung at once because of these chained boards similar to the LG.

I know the x blew the y because I started with no shorted FETs on the Y and after trying to component repair on the X and tryin to power up several time both x & y had dead FETs, buffer was ok.

But the bullet and spent the $$ on the lot otherwise I could have been chasing my tail.

[aasnowskate]

Re: LG 50PJ350 dead, relay clicking

When I disconnected the ysus (P812) and leave P813 connected I get sound that can be controlled by the volume up and down. All the voltages coming out of the Power supply board are proper according to the markings on the power supply board.