Hello,

I am trying to repair an HP 0957-2271 power supply.

The output rectifiers (VSB3200) are shorted. I am wondering what would have caused this and also what the small ferrites are for around the cathode legs?

Could I replace the rectifiers with 1N5406 instead?

Thanks.

 

Are you sure the diodes are short circuit?
Desolder or cut one leg, then test.
Good luck.............

 

Are you sure the diodes are short circuit?
Desolder or cut one leg, then test.
Good luck.............

Yes, I tested them out of circuit.

 

My apologies.
What about the mosfet/ transistor/ regulator on the heat sink.
Good luck............

 

Could I replace the rectifiers with 1N5406 instead?

Make sure the output capacitor is not shorted.
1N5406 should be a good replacement, and with any luck they will be the only faulty components.

 

Make sure the output capacitor is not shorted.

Yes, I desoldered that first to check that it wasn't shorted. All the caps look to be in good condition.

I was just curious why the output rectifiers go short?

Also, what is the purpose of the ferrites and should I try and recover them from the old rectifiers?

 

Components do just fail with no apparent cause. Old age?
Replace the ferrites if possible.

 

Components do just fail with no apparent cause. Old age?
Replace the ferrites if possible.

It's not very old and the capacitors look to be in good condition and measure within specification.

What is the purpose of the ferrites? Is there an easy way to remove the old ones, they seem to be epoxied to the legs?

 

Switch mode power supplies generate a lot of high frequency noise and the approval regulations require manufacturers to reduce the amount of this that escapes from the supply so it doesn't interfere with other stuff. The ferrites are a part of that. The supply will work perfectly well without them.