Peavey XR684F mixer repair issues

[ogeecheeman]

units lights flicker when turned on then go out.cooling fan stays on.audio is heard when signal applied to power amp in jacks.
after checking regulator voltages per enzo recommendation, found 7815A putting out 3vdc to mixer stage.checked regulator and associated components. regulator found to be shorted. evidence of heat around center pin of failed regulator.any idea what may have caused this. it is a plastic body 220 package without the metal heat sink.
thanks
gordo

[olddawg]

Does it work now with a new regulator. Does the regulator get hot? If not the part just failed. Happens all of the time.

[nickb]

The supply side input to the regulator should be at least 18V. Did you check that? If >18V is going in and 3V out it's seems that it's unlikely to be shorted. Given the discoloration and flickering lights my first suspect would be a bad solder joint on the regulator. The safest thing to to is replace it and retest. If all is normal and it doesn't get too hot it might be a good idea to fit a small TO220 heatsink to protect it and the joints.

Failing that, excessive current draw causing it to thermal limit will result in no or low output voltage. The component causing that may be running hot enough to feel.

[ogeecheeman]

still waiting on part.supply side is +/- 26vdc respectively or each regulator.7915 is right on the money.7815 is shorted.trust me.

[nevetslab]

Over time, if there is significant current being drawn thru the IC regulators and not sufficient heat sinking to keep them cool...at least less than 60 deg C, prolonged hi temp travels down the leads, and eventually will cook the solder connection Did the solder pads look crusty when you replaced the IC? Was there heating evidence on the PCB around teh solder pads for the IC? Those are usually good signs of engineering not doing their job in thermal management on a product. Peavey usually DOES do all that well, though I've never gone thru the thousands of different products they built over all the years, If there are any dip tantalum caps on the supply buses, I'd look at those...

I didn't catch a reply to the question about is it now putting out 15VDC with the product's load on the regulator. It the output has fallen low, you'll have to find what's dragging the supply down.

[ogeecheeman]

Over time, if there is significant current being drawn thru the IC regulators and not sufficient heat sinking to keep them cool...at least less than 60 deg C, prolonged hi temp travels down the leads, and eventually will cook the solder connection Did the solder pads look crusty when you replaced the IC? Was there heating evidence on the PCB around teh solder pads for the IC? Those are usually good signs of engineering not doing their job in thermal management on a product. Peavey usually DOES do all that well, though I've never gone thru the thousands of different products they built over all the years, If there are any dip tantalum caps on the supply buses, I'd look at those...

I didn't catch a reply to the question about is it now putting out 15VDC with the product's load on the regulator. It the output has fallen low, you'll have to find what's dragging the supply down.

I haven't received the part yet but yes there was evidence of heat at the middle pin of 7815a.no crust just a little tan discoloration from heat.I'll get back to you once I get the part in.I did test all of those 1N4004 diodes but found nothing unusual.I wonder if this could be related to a phantom power issue.it is a church mixer and they use a lot of condenser mics.

[The Dude]

No schematic in the thread, but phantom is usually a completely different 48V supply. It wouldn't have anything to do with the 15V regulator.

[ogeecheeman]

solved! faulty 7815a regulator.

[BOB DISDELL]

xr684f fault

units lights flicker when turned on then go out.cooling fan stays on.audio is heard when signal applied to power amp in jacks.
after checking regulator voltages per enzo recommendation, found 7815A putting out 3vdc to mixer stage.checked regulator and associated components. regulator found to be shorted. evidence of heat around center pin of failed regulator.any idea what may have caused this. it is a plastic body 220 package without the metal heat sink.
thanks
gordo

Had same problem,but found capacitor on effects board had broken joint.Repaired this fitted new 7815a regulator which had metal heat sink,this is ok because heat sink is earth but dont do this with 7915 regulator since youll get a short.These regulators take the input voltage 25v to 15v.
The initial fault was due to faulty 7815A Regulator breaking down.
Initial repair using 7815A regulator resulted in on switching on and then off sometimes the unit would fail.Found new regulator was faulty,fitted another and amp is now perfect.Bob Disdell