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Re: Marshall MB450H Schematic
It took a week and a half, but Marshall finally came through and sent me schematics. Once in hand, I found the last of multiple problems in about five minutes, had the part changed out and the amp working and undergoing torture testing/burnin within 30 minutes.
So what was it?
Crash GordonDrive It Like You Stole It
Curious minds want to know!
I hate the "I've fixed it/solved the problem" without WHAT fixed/solved it posts. Please enlighten us. Inquiring minds want to know.
Had someone before you had a similar/same issue AND posted the fix for it/details, it might've made it easier for you (and anyone else afterwards)
Although with a brand like Marshall (amps) , they want their gear working, so direct contact works well, I know Mesa Boogie/GK/Trace Elliot does.
Starting with the obvious:
one output transistor on each bank of the output stage had a C-E short.
Less obvious was a current steering transistor earlier in the circuit which was pulling the + bank toward the pos rail.
Finally, a quad op-amp near the input stage. That was it.