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Should i repair this PSU? (PT blown)

O

olmer

Senior member
Hi,

I have quite expensive out of warranty PSU which had packed up from what i assume was overheating.

2SC3320 power transistor had literally broke in two.

It is pretty cheap on its own, but would take couple of hours of soldering to get to it/replace.

I do not know much about PSUs, but the rest of the board's components look physically undamaged (checked only capacitors/coils).

Is it worth time/effort, in your opinion, to chance buying and replacing 2SC3320, or most likely some of the other components are also damaged?

There was no smoke/etc. Just blown 13A fuse in the plug itself.

TIA.
 
Honestly? I wouldn't. Aside from the cost in time and money, the smoked transistor could be a symptom of another problem, and the new one could just die immediately again. And even if that doesn't happen, you're never really going to trust the PSU again, and it's too important a component.
 
I thought of just putting 5A in a plug/moving it on RCD’d circuit and using it on a less expensive equipment. It is a high quality piece (was).

It was running 4x 5870s 24/7 for just under a year (Bitcoin mining) with a very few pauses. I bought it second hand with only 30 days warranty, but the stickers were intact/looked okay.

It is just I have no idea what normally fails along with PTs (if anything). Other PT on the same cooling plank is fine.
 
If you know how to solder, go for it. It shouldn't take more than 1 hour, assuming you'll have to unsolder everything on the heatsink, including the heatsink itself, and that's a safe assumption for 90% of computer PSUs since they're very crowded inside.

That power transistor is in the high voltage section and therefore needs properly electrical insulation from the heatsink with a sheet of silicone rubber or mica and possibly a plastic washer for the screw or it will short. The exact insulation hardware depends on the particular packaging of the transistor, and here's some information about that:

http://www.instructables.com/id/Semi-Conducting-A-Guide/step1/Packages-an-Stuff/

Never use Arctic Silver.

Are there only 2 power transistors on the plank? If so, the other one may be for the standby +5V supply (but that transistor or IC is often mounted alone, without a heatsink). Typically PSUs rated for more than approx 100W that use NPN high voltage transistors use 2 of them together, arranged push-pull, and both fail together.

In practice any replacement transistors do not have to be identical to the originals but only match the general characteristics - NPN, maximum voltages, current and power ratings, and fit the same physically. High voltage transistors from old PSUs usually work well and are probably safer choices than some offerings found on Ebay.

You should test all the diodes and transistors with a meter, while the AC is unplugged for safety, of course.

Do not run the PSU with its case opened.
 
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