1976(?) Roland JC 120: a little help?

echodeluxe

Member
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1,022
long story short, I have a JC 120 that amp_surgeon and I attempted to repair years ago (apparently dead FX pcb) So we removed the pcb to diagnose it. ran out of time and it was in storage forever. we took photos of the wiring to the board so we could remember how to put it back together, but we can't find them OOPS.


also, we can't seem to find the correct schematic, as there are like ten of them. here are some photos as it currently sits:












any insight on a correct schematic, or photos of the same version of amp would be super duper helpful.

also, we're the original speakers 8 or 16 ohms?

thanks
 

teemuk

Member
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3,264
Yes, many, many different versions and not all schematics circulating in Internet. Try Roland, if it fails then try if any of early JC-120 service manuals are close enough for reference. If referring to serial numbers doesn't help then you can compare little details that existed in production only for short periods, like if there's a "chorus trimmer" pot in the rear or not. The service manuals should at least portray internal layouts and wiring between them. Greatest changes past that point (in just plain layout and wiring of the boards) are usually in wire colours only. The circuitry changed but usually board-to-board wiring and layout remained somewhat consistent. With that in mind, issues of the FX board can be much more painful to fix since the early chorus/vibrato circuit has an astounding amount of variation and you probably will need the exactly right schematics for proper reference. Pick a new-enough (e.g. post '82) diagram and the chorus/vibrato circuit design is completely different than in the older amps.
 
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echodeluxe

Member
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1,022
thanks for the help!

luckily we found the original photos of the chassis before we removed the board. problem pretty much solved for now. I'll post progress!
 

echodeluxe

Member
Messages
1,022
MISS IN ACCOMPLISHED



works like a charm. all the effects work. Loud as hell. one original speaker and one vintage 30, 16 ohm. sounds great. has a little hum I'd like to figure out but beyond that, it's awesome.
 




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