Packard Bell PB70 PSU repair

[Formulator]

Here is a PSU from a PB300 386SX desktop.

At first the 12V rail was reading only ~10V so I took a peek inside to see if adjustment could be made. There was a small dial but the head rather easily snapped off. Now the PSU will not output any voltage. Other than replacing the part I do not know how to fix voltage problems.

 

[Malc]

It's a 'Preset' or potentiometer / Variable resistor, It probably has a value on it somewhere, It controls the output of the PSU and are preset at the factory so usually no need to touch it unless it's failed of course. Look for bulging / leaky Caps.

 

[GearTechWolf]

The capacitor at the left (touching the bundle of red wires) appears to have a bulging top, so it has probably failed. There are likely others that have failed or are near failure, either close inspection or replacement of all large value caps would be prudent. Unfortunately, it looks like the wiper (the variable part of the potentiometer) broke off with the knob, so that is probably why you no longer have voltage on the +12 rail. The characters/numbers between the two legs of the potentiometer should identify its value and help you get a replacement for it. Then, you will probably have to find the right setting for it by trial and error, unless you have another unit you can reference for a good starting point. Hope this helps!

 

[Chuck(G)]

If you remove the remainder of the pot from the PCB (and maybe even if you don't--but you'll have to eventually), you can get its value for replacement by measuring the resistance between the two outermost legs. These are usually linear taper, but that hardly matters in this case.