Samsung OLED QN77S90 Bad Power Supply

[cheebster]

Hello, picked up this tv a nice Oled QN77S90. However, it's blowing fuses like crazy (got the whole room lights go out the first time). So i digged and it seems this tv has the BN44-01264A PSU that often fails. However, replacements are costly (samsung replaces it for the BN44-01329A revised psu).

I'd like to troubleshoot that one. Here is a picture of it, but honestly i don't know where to start. It blows a 12A fuse in a split second, it's really a hard short on this one. Thanks for any guidance !

[Davi.p]

The fuse rating is somewhat crazy! The near marking says 8,5A, if at 230v, is close to 2kw, like an oven!
Remove the near VX varistors, and test again .. check the back cover for maximum power rating, then select a better fuse..

[cheebster]

I found a short on part GP47S60YERD which is a huge IGBT on the right large heatsink, shorted. Ordered from digikey, hope it fixes.. Can i test the psu without it ?

[cheebster]

The ac input fuse is a T12AH250v 12a fuse.

[Davi.p]

Sorry i misunderstood the fault description, about the fuse, that H sound strange, AH is Ampere per hour, usually written on batteries..

[cheebster]

With this IGBT removed, psu powers on and clicks, and produces output voltage. Safe to test on tv without it ? IDK. Will wait for the digikey part, i guess.

[Davi.p]

right heatsink is for PFC circuit, but so powerful board with a single diode bridge, sounds strange to me, check that, an open diode can make pfc circuit suffer a lot... the igbt is probably paralleled with another, i need to see the back side, but no need to hurry it , better to wait the replacement or test it only with dummy loads

[cheebster]

I will have a replacement power supply tomorrow, so i'll see from there. Thanks

[cheebster]

Ok ! Got my replacement ebay psu. Came in with a blown fuse and same short at the same location. I guess i will need to find the culprit. Digikey found me a replacement for the ic, a IGP20N60H3XKSA1 (smaller format but should have worked) and when plugging in, a hole blew in the psu in one of the traces. I need to troubleshoot this one better, it seems. If anyone can shine some light on where to start.. Thanks

[lotas]

Well, that means it (the power supply) was not new, but used and, moreover, not working properly, it had to be returned to the owner...

[cheebster]

That's fine. I need to find what's wrong with these, still.

[cheebster]

From here; https://www.reddit.com/r/S95B/commen...ites_the_dust/ it seems these are a common failure. Defective psu is BN44-01264A and new psu design is BN44-01329A but hard to find.

[Davi.p]

Mate, without back side picture is not possible, i know schematics are like Graal cup, but wait for the sun light..

[cheebster]

Here is the back side..

[Davi.p]

This is a new design for me.. needs more observation, igbt are working in couple i guess, push pull or paralleled, need them to.be replaced both in same moment.. i rapidly watched photo yesterday, i see two transistors and a diode on heatsink, so it means probably igbt are paralleled, more reason to change both, needs also to check bigger caps parameters..

[lotas]

Why did you assume that GP47S60YERD is an IGBT? It is actually a MOSFET transistor.

[Davi.p]

cheebster said so, i do not know..

[cheebster]

I replaced it finally the GP47S60YERD with IKW50N60DTPXKSA1 which works fine. PSU outputs all his voltages fine. However, tv still flashes red and wont fire up. Guess the panel is bad on this one.. 2 flashes.

[Davi.p]

So A13V=13v~, Vamp=18v, Vdrv=32v?

[cheebster]

Yep!