Hey everyone, I've been struggling with a repair for a while so I figured it was time to reach out to some more knowledgeable people.
I have an Akai 50" plasma TV which uses LG internals that I'm trying to repair. I narrowed down the problem to a faulty IPM module on the Z-Sus board. I don't have a picture handy but it is similar to the attached image that I found online. These modules are quite atrociously priced online and most of them look like they have been salvaged from other TVs. My IPM was full of potting compound so I dug it all out and it turns out there isn't much in there. I found that the two main MOSFETs were shorted, along with some blown SMD resistors and diodes. I managed to find the exact replacements for all of the components except the MOSFETs as they are bare die FETs covered in a glob of hard resin.
I scraped the resin covering the old FETs off and desoldered the rest. I then replaced them with some Panasonic 5N2307 FETs that were salvaged from a dead Panasonic plasma. There are no datasheets for these FETs but as far as I can tell they are 230V 25A. I replaced the blown fuse on the supply rail and fired up the TV. I got a good image and figured I had won. However, ~1 min later, the TV suddenly shut off. The fuse was blown again and both FETs were shorted. No other components were damaged. I figured I might have got unlucky and salvaged a partially damaged FET so I grabbed two more and tried again. Same result. TV worked for ~1 min then shorted both FETs.
So I figured these FETs were not up to the task so I tried some FDB12N50TM FETs that I had on hand. These are 500V 11.5A FETs. After Installing them, I powered up the TV and saw that the screen had a lot of ghosting and bad colors. I let it run for a good while and the FETs never blew. However, there must be something about them that is not suitable for the application. I am thinking it has to do with the switching rise and fall times but I have no way to confirm this.
I found this video highlighting the same problem that I was having and the guy used STD12N60DM6 FETs. These are 600V 10A FETs. As a last resort, I ordered some of these and installed them. The TV powered up and the image was perfect, no more ghosting. However, after a few seconds one of the FETs forcefully detonated with the volume of a gunshot.
I have no idea what FET to use and trying random ones with seemingly appropriate ratings has not worked. The supply voltage Vs is about 196V so I'm not sure why this would be shorting the 250V Panasonic FETs. The FDB12N50TM FETs were not damaged, but something about them was causing a poor image. The STD12N60DM6 has a higher voltage rating and only a slightly lower current rating than the FDB12N50TM, but they exploded forcefully when used.
Could someone please explain what specification I am neglecting to consider that would explain these behaviors? And even better, could someone suggest a suitable replacement?