Seeking Crate PM-20 Schematic or Photos of the assembly board

[60Hz]

I'm troubleshooting an older Crate PM-20. The assembly board is 06-220-01.

I suspect there were previous repair attempts and I fear there may be missing components. If anyone has a photo of the board or schematics, it could be a big time saver for me. Thanks.

[Enzo]

Shouldn't be a complex little amp. What is wrong with yours, and what leads you to think parts are missing?

[glebert]

I wonder if they may have reused some of the design of the CR-1, which was also a simple 20 watt combo in a wooden box?

[60Hz]

Thank you for the responses. I got it working!

I reviewed both CR-1 and B10 schematics. While neither is an exact match, they were just enough help. What confused me were some leads in the power supply section. They almost looked like test point leads. But turned out to be remnants of a diode in the rectifier bridge for the +17 Volt side (photo). This is where the other schematics came in handy. This is showing my lack of experience, but I was previously unaware the power supply used a full rectifier bridge and set up both +17 and -17 Volts. (I mean I had my suspicions, but want more proof.)

In the end, I had to replace one of the 3300uf (swollen read 2200uf), two 1N5392 diodes (one totally missing), two TIP31C (shorted), and two 100 ohm resistors (smoked like due to shorted TIP31Cs).


Here is the photo of the part that confused me initially. Had the leads been pointed toward each other, then it would have been more obviously a dead component; at least to me.

[glebert]

That is pretty strange the lead was pointing the other direction. Good job getting it working!

[Enzo]

Part overheats enough to crumble, hot enough to melt the solder, the wire part moves, a moment later the solder solidifies and the wire is locked in its new position.