Phihong PSM-5341 blows fuse after recap?

[Steve]

Hey guys,

Sorry this one has stumped me... I've recapped lots of these PSUs for people recently without any issues, fairly basic nothing too tricky involved. I tested before the recap and all was fine, after the recap the fuse keeps going.

The only thing other than recap the PSU is I pulled the IC2 MOSFET up a little by melting its legs and pulling it though a little. I do this on all my recaps of this PSU because by default that MOSFET is too bent over which heats up capacitor C19 which I don't like.

I've tested everything I soldered with a multimeter, no shorts from what I can see. Any ideas welcome.

PXL_20210709_111345803.jpg (357.61 KiB) Viewed 2075 times

PXL_20210709_111402331.jpg (421.05 KiB) Viewed 2075 times

PXL_20210709_111422772.jpg (411.73 KiB) Viewed 2075 times

[Steve]

A close up of IC2 and C19:

PXL_20210709_112006608.jpg (292.93 KiB) Viewed 2074 times

[exxos]

Fuse blowing tends to be mains side issues. The low voltage side has basic trip out on faults...

I would check the main switching transistor isn't shorted first of all. Also check for shorts around the small ic.

[czietz]

Looking at https://www.exxosforum.co.uk/atari/last/ ... 5341rc.jpg the big red mains voltage capacitor has its negative terminal (white stripe) on the other side. Thus, I assume @Steve got the polarity wrong (and is lucky that it didn't end in "fireworks"). The capacitor might have been damaged in the process and should be replaced once again.

PS: Not that it is relevant here, but IC2 is not a "MOSFET" (as mentioned in the initial post) but the -5 V regulator.

[Steve]

@czietz Thanks ! I can't believe I did that! Must have been too tired, but yeah, this is why the forum is so helpful for a second pair of eyes!!! Cheers. Hopefully the cap is ok I'll run it through my tester to make sure, the fuse blows instantaneously so it was probably protected.

[Badwolf]

Looking at https://www.exxosforum.co.uk/atari/last/ ... 5341rc.jpg the big red mains voltage capacitor has its negative terminal (white stripe) on the other side.

Great spot. Remote PSU debugging. Love it.

BW