pontiacpete 5/16/2018 6:55 AM
Ampeg pf500
This amp came in with a cutting out problem. Amp plays fine then the sound cuts out and fault light comes on. I soon find that This happens also when hitting the top of the unit. I open up and start tapping around the board with a chop stick. When tapping on one of the two heat sinks in the middle of the unit(there are 3 heat sinks) the unit goes into fault mode. The weird thing is that it doesn't take much force to get it to cut out. In fact a very light tap on the sinks does the trick. Tapping the board does the same but with more force.
So I think it's a solder joint. Flip the board and solder the transistors attached to these sinks and other large solder joints around the board. Still the amp cuts out. Second time flipping the board I solder more joints and then tighten screws to heat sinks, 4 all together. Now the amp stays in fault mode. No sound at all.
I'm not sure if I'm just sharing this experience or will I even try to repair this thing. One part of me wants to remove the heat sinks and transistors and rectifiers off the board and see if anything is revealed.
What would you do in this situation?
thanks
 
g1 5/16/2018 12:58 PM
Check for cracked legs on those transistors mounted on the heatsinks.
 
pontiacpete 5/16/2018 3:34 PM
Problem here is desoldering some of the transistors off this double sided board. There's no room to unscrew some of them from the heat sink.
 
glebert 5/16/2018 11:50 PM
I have almost this exact same problem with my SVT7 Pro. The PF500 board looks almost identical to the 7 Pro except a few less components (500W instead of 1000W I guess). Mine seems to cut out when I tap on one of the class D driver ICs though. I think the FETs you are showing are for the SMPS for the main voltage rails, though. Should be able to monitor the rails and see if they drop out when you tap, and see if it is one vs. the other.