Power Supply Questions

[Siegfried Meier]

Hey guys,

I have a Behringer Rev2496 here with a bad power supply.  It appeared that 2 resistors were burnt out, so I replaced those (with standard size, mind you, not SMT).  I'm measuring the same voltage on the output as a known good supply - 30vdc, 5vdc & 15vdc.  However, it still won't power the mainboard.

What could I be missing here?  I've noticed that on the good supply, there's a 100pf cap that seems to be melted to one of the smt resistors (same as the one I changed in the bad supply).  This would appear to NOT be good, but this power supply works fine.

How can it be that I read the same voltages, but this one does not work?

Any help much appreciated.
Thanks,
Sig

 

[Blue Jinn]

A schematic would help. However, look for shorts on the main board. I had a similar fault with an ARP synthesizer.

 

[bkbirge]

Are you measuring the power supply with the load attached? Unloaded power supplies can look fine but go straight to hell when loaded if the regulator has gone belly up.

 

[abbey road d enfer]

Hey guys,

I have a Behringer Rev2496 here with a bad power supply.  It appeared that 2 resistors were burnt out, so I replaced those (with standard size, mind you, not SMT).  I'm measuring the same voltage on the output as a known good supply - 30vdc, 5vdc & 15vdc.  However, it still won't power the mainboard.

What could I be missing here?  I've noticed that on the good supply, there's a 100pf cap that seems to be melted to one of the smt resistors (same as the one I changed in the bad supply).  This would appear to NOT be good, but this power supply works fine.

How can it be that I read the same voltages, but this one does not work?

Any help much appreciated.
Thanks,
Sig

There's probably a reason why these resistors have burnt. It may be a short, but since you say the voltages are correct, either ther was no short or the short is gone. That probably means that one or several other components have burnt also. I think the indaicated voltages are rather strange: +5 for digital is ok, +15 for analog also but -30 ???. There should be a -15 rail...
Apparently, you also have a working unit. You must compare the other voltages. For example, check the +/- rails on the opamps.

 

[Siegfried Meier]

Ahh yes you are correct, I was testing with no load.  I can't see anything else that's burnt out, but I'm sure an IC or 2 could have cooked and I'd never know it.

I'm determined to figure this thing out, even if it's nothing more than a good lesson in repairing these kinds of things.  How do I begin this?  How do I test IC's, either in circuit or out of circuit?

Any help is much appreciated.
Thanks!
Sig