Carvin PB200

[xtian]

A friend gave me his project amp, Carvin Pro Bass 200. Schematic:

http://carvinimages.com/schematics/P...00%20Rev-I.pdf

He claimed the output transistors burned out, and had replacements on hand. He had unsoldered one side's NPN and PNP output transistors, and gave it to me in that condition.

I measured the pulls, and they seem fine, so I'm not confident about his diagnosis. Anyway, I put in the new transistors, and powered up with a bulb limiter. I get 32vDC on the output, so that's not cool.

Please suggest next steps.

[xtian]

No takers? If I have DC on the output, does that absolutely indicate bad transistors?

[Leo_Gnardo]

No takers? If I have DC on the output, does that absolutely indicate bad transistors?

Welllll, could be! You already checked the output transistors and they tested OK, right? Now it's onto all the remaining transistors, diodes too, resistors, caps are all suspect. Fixing transistor gear is so tedious. Any amp component fails and you start smoking speakers. Phooey! And if you do find a failed component, that doesn't mean it's the only one.

[Enzo]

Yes, a bad voltage amp transistor three stages before the outputs can cause this. Almost anything can.

[g1]

Does this have 2 power amps like the schematic shows? If so, is the one amp still working right? Then you can compare measurements to the good side to help narrow down the problem.

[xtian]

No, both sides have failed. Thanks for the heads up!