Can anyone help with a non functioning Pyramid Power Supply

[JoshuaHufford]

Just picked this up at a sale really cheap, seller did not know if it worked. Didn't have a meter with me but I was able to plug it in, the lights came on and I heard the typical hum when it came on so I thought I'd take a chance.

Got it home, put my meter on it, at first the meter shows 14V DC but it quickly drops to 8V DC and holds there, I have not tried it yet with a load.

Took the cover off, don't see anything obviously wrong but I did notice something around the 2 capacitors. Does this look like they are leaking or is that some sort of glue to keep them from moving? If they are leaking I can replace them easy enough.

 

[bharvey2]

It's kind of hard to tell from the photo. At first glance I'd say its adhesive but I only see it at the base of the two large filter caps. It isn't unusual for manufacturers to glue down large components as you probably know. Are the caps deformed in any way? That could be a clue as to whether they've gone bad. It wouldn't hurt to change them.

As far as the voltage dropping, if it were mine, I'd check the transformer output voltage first and it looks like it could be measured at the two red wires (assuming they come up from the transformer below) between D1 /D2 and D3/D4. If it's several volts (AC) above the desired output voltage, it's probably okay.

Lastly D4 looks discolored or maybe a bit burned. Is something wrong with it? If it has the same stuff on it as does the base of the large capacitors, then my vote would be for adhesive.

 

[JoshuaHufford]

Thanks for the help. The same material is on D4 that is on the capacitors, there was a small string of the same material between the dioed and the capacitor, that is what was making me wonder if maybe a capacitor blew something out of it or if it was just glue from the factory.

I don't see any deformation of the caps, but I can't see the bottom without removing them, I might unsolder them next chance I get. I'll check the transformer output as well, thanks for that tip.

Also to give an update I put a load on it, a 12V fan that probably pulls about .5 amps, the protect light comes on and voltage goes to 0.

 

[bharvey2]

I've seen the results of a few cap failures. Gross failures leave holes while less dramatic ones have failed with a little bulging or maybe no visual evidence at all. Spewing material upward toward the diodes would likely show some physical damage to the caps. My guess is that its adhesive. A schematic of the power supply would be your friend about now. I haven't worked with Pyramid power supplies so I don't have any experience to say where a likely failure point may be. The supply and rectification circuitry looks fairly simple from the photo. Unless you can find a schematic, it looks like you'll need to map out the regulation circuitry on your own, a pain but it doesn't look too overwhelming.

 

[JoshuaHufford]

Thanks for the help, I'll see if I can find a schematic.

 

[delaware74b]

Remove all traces of that brown glue. It was actually tan in color when new. As it is exposed to heat, it becomes conductive. I had a power supply in a SFF (small form factor) computer short out because of the glue.

 

[prcguy]

I would measure the voltage at the stripe end of D4 with and without a load. That will be the same potential as the filter caps and should be in the 18 to 22V range with no load and will get pulled down some with a moderate load, but should always be above 16V or so. That can tell you if the problem is in the regulator or upstream like an open diode, etc.