[Solved] LG plasma TV - Y sus IGBT substitutes running hot! - Page 1
Forum section: electronics / repair

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 30, 2022, 05:52:58 pm
content: I'm having some fun with a 60PH670S plasma TV.Originally no display Y-Sus (60R5-Ysus) board shorted.Found 3 shorted IGBT's on sustain output (Q402 on high side, Q559, Q564 on low side), MOS Q509 on set down and R251, D603.My usual supplier didn't have any of the original references. I substituted TK8A60DA for FCPF11N60.Supplier suggested RJP63K2 as a substitute for original RJP30H2A, not having found anything closer available I followed this route.All 6 IGBT's (including the 3 that survived) were replaced for better current sharing.TV is now working but low side IGBT's get very hot. Thermal camed at 110°C through PCB for the hottest after 5 minutes running so I'm quite concerned about the junction temperature...Although the datasheets I've found don't mention internal diodes, the substitutes seem to have one while the originals don't. There are freewheel double diodes on the PCB (SF20D400SD2).Are the internal diodes a good enough reason for the high temperature? They could could have a lower Vf than the external ones and dissipate extra power, the VCE sat is also slightly higher.I feel it can't be left as-is and relaible, but feel a little stuck for solutions other than lowering thermal resistance.Any ideas?

author: shakalnokturn
author_rank: Super Contributor
timestamp: December 01, 2022, 10:17:24 pm
content: Small update:As I had 3 remaining original RJP30H2A that weren't blown I swapped those back on the sustain low side. They run cool...TV works but even playing with adjustments I can't get a decent image with pictures having a high white content.Conclusion is that RJP63K2 are not an adequate substitute.Now where to find a reliable source for original references?Anyone with a dead Y sus board willing to sell me a few pulled and tested transistors?Edit:Added new thermal photo. This time the hot points are the high side transistors, not as bad as the low side ones were but still much hotter than normal.Also to be noted that this time the hottest component on the low side is the freewheel diode.

author: fzabkar
author_rank: Super Contributor
timestamp: December 01, 2022, 11:29:04 pm
content: Same part, different package:https://www.digikey.com/en/products/detail/rochester-electronics-llc/RJP30H2DPK-M2-T0/12131525https://www.datasheet-pdf.info/attach/1/5708273332.pdf

author: shakalnokturn
author_rank: Super Contributor
timestamp: December 01, 2022, 11:42:59 pm
content: Thanks fzabkar,I came across that one, unfortunately the package won't fit in my situation.I also considered mounting some of my pulled spare TO220 IGBT's on the small heatsinks on top side of PCB but then that means running the gate terminal through the drain copper plane maybe I could get away with that on the high side as the drain sits at 200V DC, seems a bit ambitious to attempt on the low side where the drain is switching between 0 and 200V...

author: shakalnokturn
author_rank: Super Contributor
timestamp: December 06, 2022, 12:35:44 pm
content: Today I wanted to find out more with a quick test setup:One lab power supply to set Vge at 15V, another for collector current.It turns out that even at 5A VCEsat. is already at twice the maximum stated for 35A in the datasheet...At 10A the collector tab desoldered itself from the copper plate it was attached to for the test.No surprise they were running hot in the TV!Conclusion is that -once more- ASWO has sold me fakes.

author: shakalnokturn
author_rank: Super Contributor
timestamp: December 08, 2022, 10:06:35 pm
content: As a happy end to this chaos:Not knowing where to turn for reliable transistors I decided to use IGBT's from my scavenged parts collection.I had some RJP variant with slightly lower Vceo (300V), same current capabilities, very similar switching times but unfortunately much lower power dissipation due to TO-220FP.Nevermind encapsulations, I'd wasted enough time on this and just had to get it finished without too much extra cost, the tab insulation was crushed away with a vise-grip then collector lead cut short.Exposed tab was soldered in place of TO-263 originals and thermal path improved with added pieces of 2.5mm² copper wire.Both high side and low side sustain transistors run at about 55°C for the hottest, TV has run several hours already with a normal picture after readjustment. Trimmers are almost back to factory positions.

author: inse
author_rank: Super Contributor
timestamp: December 09, 2022, 05:59:39 am
content: That’s hardcore repair, just the way we like it :-)