SAMSUNG plazma TV repair. - Page 1
Forum section: electronics / repair

author: Refrigerator
author_rank: Super Contributor
timestamp: September 28, 2016, 06:45:07 pm
content: My cousin dropped off a SAMSUNG plazma TV to repair.The TV had a snake living in it for a while and it messed one of the power boards up.The board in question islj41-06004aand so far i have replaced a blown stand-by SMPS IC and three IGBTs.The SMPS IC had it's top completely blown off, but i tracked the exact chip through the pin-out and replaced it.The three failed IGBTs were all shorted between all three pins, two big ones (TO-247) and one smaller one (TO-220FP).Before the replacement the TV tried to power up but failed, then tried again and so on.After the replacement the TV screen briefly flashes some image in the screen, same happens during power-off, there is no more power-on failure.The image is broken up, only half or less horizontal lines flash and only for a split second on power-on/offThere are two large heatsinks and a smaller size one on the board.When powered on one of the big heatsinks and the smaller one, both with power IGBTs get hot but the other large one stays cold.The cold heatsink has a pair of TO-220 IGBTs on it and a bunch of diodes, since it stays cold i suspect it's got a fault around it.Maybe anyone here has dealt with plazmas with similar failures ?Thanks.

author: tautech
author_rank: Super Contributor
timestamp: September 28, 2016, 07:41:58 pm
content: Have you put a scope on the PSU LV side and checked for ripple?After a catastrophic PSU failure there could be diode damage and I've also seen bad caps do funny things to TV's behaviour.

author: Refrigerator
author_rank: Super Contributor
timestamp: September 29, 2016, 02:29:27 pm
content: Quote from: tautech on September 28, 2016, 07:41:58 pmI haven't checked the PSU LV with my scope but i have tested a few caps and all of them read low on capacitance but OK on ESR ( eg. 220uF will read 200uF, ESR = 0.15)

author: tautech
author_rank: Super Contributor
timestamp: September 29, 2016, 05:58:26 pm
content: Quote from: Refrigerator on September 28, 2016, 06:45:07 pmThis reminds me of HV faults in a CRO....similar on-off behaviour.At power on voltages rise into the limits where the TV will briefly operate then either ripple or some other parameter is wrong and the image disappears.Power off is the reverse.Suspect PSU IMO.

author: Refrigerator
author_rank: Super Contributor
timestamp: October 09, 2016, 11:34:26 am
content: Allrighty then, so today i finally found some time to work on the TV again and i checked all the other boards but didn't find any other faults.While checking the boards i found that one of the flat flex cables that was going to the aforementioned board was damaged and had to be replaced.I dug around in my box of flax flex cables but didn't find any direct replacement so i made a cable from other bits and pieces.The cable turned out well and i decided to plug the TV in and see if it works with the fixed cable.At power up it had a pattern of white noise ( with colors ), which washed out and a moment later the TV came back to life with a "HFMI 1" and a "no signal, check signal cable" on the screen.All was well untill about 10 seconds later the TV blew again.The two big IGBTs that i had replaced blew in a way that all three pins are shorted together, just like the first ones that i replaced, the heatsink they were on got warm quite quickly as well.Also when the image came up on the screen it was not sharp, the edges of rectangles were ever so slightly fuzzy.So the TV works but i can't keep replacing IGBTs for 10 seconds of operation, i guess i'll have to put some fatter IGBTs?

author: Rasz
author_rank: Super Contributor
timestamp: October 09, 2016, 04:31:44 pm
content: Quote from: Refrigerator on October 09, 2016, 11:34:26 amusually when stuff blows up in teams there is a short somewhereyou even mention heatsinks getting hot, measure upstream form the supply you fixed and find what is shorted/low resistance