HK Polar 10 PSU Breakdown

[MoonsTaBass]

Hi everyone !

I need some advices with a strange failure.
A friend brought me a HK audio Polar few month ago that has his power supply in short.
I replaced the three power mosfet (WMK38N65C2) and the oscillator (irs21867s) was bad so replaced too.

The think is that I didn't find the original WMK38N65C2, it seems "obsolete".
So i found a WMK36N65C4 pretty close to the orginal but the drain current isn't the same...
However I tried and in fact it worked !
My friend did about 20 gigs and everythink was ok but one day it blowned again. It blowned at startup (like the first time).

This time I only have one mosfet dead, oscillator is ok. I wonder maybe it's because it's not the good one.
I found this one WMK38N65FD seems to be more close to the original WMK38N65C2 BUT internal resistance is a little but higher so i wonder about overheating ?

What do you think about it ?

Thanks,
Antoine from Belgium

[The Dude]

Did you get the parts from a reputable source? There are lots of Chinese fakes out there.

[x-pro]

If he operated it for 20 events, the transistor was fine. One is left wondering why it burned out the first time. It came from the factory with original parts.
Did it burn out the second time in the same way? Perhaps the owner of the unit is not operating it properly.

[MoonsTaBass]

Hey !

"Did you get the parts from a reputable source?"
Yes it's from TME.EU

"If he operated it for 20 events, the transistor was fine. One is left wondering why it burned out the first time"
The first time it burned, I think it's because of the oscillator. so the transistors was open at the same time and it short them....


"Did it burn out the second time in the same way? Perhaps the owner of the unit is not operating it properly."
Now there is just one transistor dead, oscillator is good. It always blown at startup, just push the on/off switch and... BOOM.

I just wonder the difference between WMK36N65C4 and WMK38N65FD.
Is one is better than the other to replace the original WMK38N65C2 ?

Antoine

[g1]

I just wonder the difference between WMK36N65C4 and WMK38N65FD.
Is one is better than the other to replace the original WMK38N65C2 ?

36 is only rated for 20A current, 38 is rated for 38A. I think it may be better to stick with the 38 version.

[MoonsTaBass]

Hi !

It's exactly what I thought But question is, what about the internal resistance "on state resistance" ? and what about the mosfet technology (C4, C2 and FD) ?

Thanks