PPI A600.2 Troubleshooting Help

[digitalloving]

I've had my Precision Power A600.2 amplifier for over 10 years now and it is, in my opinion, one of the best amps ever made. That being said, I recently plugged it in and it doesn't drive speakers anymore. The power light illuminates green and everything seems to working correctly. However, the first thing I noticed about the start up process is that no "thump" was generated when the power was connected. The fuse is not blown. Also, connecting and disconnecting the RCA cables didn't produce any noise through the speakers. I used another amp to check the speakers and they work correctly.

These symptoms lead me to believe that something on the amplifier is amiss. Normally, I would chalk this up to bad luck and purchase a new amplifier. However, the amplifier is extremely dear to me as I have had it for many years and it has a lot of sentimental value to me. It is also very ugly, which I like too.

I've taken a picture of my sickly amplifier in the hopes that someone can spot the problem with it. If not, any direction on ways to troubleshoot the issue would be greatly appreciated. Also, I searched the forum but may have missed a previous topic that outlines how to do this. An old fashioned point in the right direction is definitely appreciated as well.

The fairly high resolution picture is here....
http://scwru.com/PPIFull.jpg

[Perry Babin]

Try pushing the rectifiers (2 legged devices mounted to the heatsink near the power supply FETs) to the side to see if the legs are broken on them.

Don't power this amp up without the cover being clamped down. If you do, you must monitor the temperature of the heatsink mounted components VERY carefully.

[digitalloving]

Thanks for the response Perry,
I've read other posts on the forum about the PPI amps and learned that I should not test it with the cover open. Thanks for the warning, because I wouldn't have assumed it would be an issue.

I'm at work now, but I'll check out the rectifiers when I get home tonight.

[digitalloving]

I checked the rectifiers and they seem to be firmly connected to the board. Although the bottom of the legs seem to have a tad bit of corrosion. I'm not sure if this would cause the issue or not. It seems that all the power supply fets "feet" have the same sort of look to them.

I've uploaded a closeup of the rectifiers so maybe someone can see something I might have missed.
http://www.scwru.com/rectfeet.jpg

Again, any additional information is more than appreciated.
Thanks again.

[Perry Babin]

I've seen a lot of those break but if yours are OK, you'll need to measure the voltage on the power supply driver IC. It's likely to be an SG3525. Look up the datasheet for it (so you can see how the pins are numbered) and post a list of the voltages on each of the pins.

Set your meter to DC volts. Power up the amp (including remote) and connect the black meter lead to the ground terminal of the amplifier. For a minute or so, monitor the temperature of all of the components along the sides of the board. If none get hot, measure the voltage on the pins of the IC. Don't slip and short between pins Do this with a 10 amp fuse in the main power line feeding the amp.

Post the voltages like this:

Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Pin 15:
Pin 16: