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Broken PSU? Answered

 I recently seen an instructable on converting an old computer PSU into a lab power supply. I followed it correctly, connecting the orange wire to the brown, the green to black and a 10W Wirebound resistor across red and black. The PSU turns on and all of the voltage rails work (although some are out by +-.75V sometimes), but I can hear a faint screeching noise and the fan doesn't spin. 
I though the screeching may be normal because all I normally hear is the fan, is this okay.
The fan is rated at 12V 0.3A, but when I measured the voltage over it, it was only 3.4V, why is this and how do I fix it.

Any help appreciated, Thanks. 



Best Answer 8 years ago

Are you sure it was working before piddled with it?

Which instructable did you use?

Did you follow the directions?

That screeching sound may be the sound a dying power supply makes.

I only recently removed it from my computer and is was working perfectly there.
I followed this instructable and completed every step.
After some more experimenting, I put a load resistor on the +12V line as well. This made the screeching less audible, but it is still there and the fan still wont turn.
I don't think it is dying because all the voltage rails still work, just not very precisely (-+1.5V of rating).
Is it possible that a load resistor is required on all voltage rails - I tried to contact the manufacturer (FSP) but their e-mail and phone number don't work?

Thanks again

Computer ps's are switching supplies and sometimes they make noise that changes when they are loaded.

Also some supplies do not regulate very well unless they are running a load.  Put a load on the 5 volt and measure it.

I don't know why the fan is not working.  On all the ps that I've worked on the fan ran anytime the supply was turned on.  It could be that the fan doesn't turn on until the ps heats up.

I am using two 10Watt 10Ohm resistors, one on the 5V line and the other on the 12V line. With the resistors in place, the lines are more stable.

I might just cut the fan connections and attach it to a 12V line to make it work.

Also, would you advise using a load resistor on the 3.3V line as well?