Someone brought me an early 1980s Carrotron C-821 Preamp Pedal for repairs, and it is proving to be a nightmare.
Of the ten BJT transistors in it, whoever built it deliberately erased the part numbers on six of them. Other parts were installed with value markings hidden against the PCB. There's one glass diode that may be a Zener, but it has no legible markings on it.
These were reportedly designed by a guy by the name of Carl Margolis, and it seems clear that he took steps to make his design difficult for anyone to copy. I have no idea if he's still living, but the downside of that approach is that it makes diagnosis and repairs pretty frustrating.
I could draw out the circuit, but that may quickly make a repair cost more than the thing is worth. I found one bad transistor that I replaced with a PNP transistor because the other unmarked ones that appear physically similar and the same color are PNP, but that didn't fix it.
Of the ten BJT transistors in it, whoever built it deliberately erased the part numbers on six of them. Other parts were installed with value markings hidden against the PCB. There's one glass diode that may be a Zener, but it has no legible markings on it.
These were reportedly designed by a guy by the name of Carl Margolis, and it seems clear that he took steps to make his design difficult for anyone to copy. I have no idea if he's still living, but the downside of that approach is that it makes diagnosis and repairs pretty frustrating.
I could draw out the circuit, but that may quickly make a repair cost more than the thing is worth. I found one bad transistor that I replaced with a PNP transistor because the other unmarked ones that appear physically similar and the same color are PNP, but that didn't fix it.
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