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Roland JC-120
Roland JC-120
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Old 1st March 2020, 07:45 PM   #1
ronjg is offline ronjg
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Default Roland JC-120

I have a Roland JC-120 (serial# 728284) that Has a relatively loud 60Hz buzz through the speakers. Also, no audio. None of the fuses are blown. I need the correct repair manual for that version. Also if anyone has any suggestions on what may be wrong, I'd really appreciate it. I'm thinking rectifier diodes or filter caps. The bridge rectifiers in this version are individual diodes as opposed to a single bridge rectifier brick.

Thanks,
Ron

* edit: Bridge rectifier diodes and Filter caps all test okay.

Last edited by ronjg; 1st March 2020 at 09:40 PM. Reason: updated information
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Old 1st March 2020, 11:16 PM   #2
MAAC0 is offline MAAC0  Portugal
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Check rectifier / caps and for loose ground wire / solder pads connections.
No audio mixed with the buzz ?

Schematics from google search attached
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File Type: jpg JC-120_s-n 380100-- 410599.jpg (728.7 KB, 38 views)
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Old 2nd March 2020, 12:44 AM   #3
ronjg is offline ronjg
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[QUOTE=MAAC0;6104947]Check rectifier / caps and for loose ground wire / solder pads connections.
No audio mixed with the buzz ?

Thanks very much for the schematic! I checked all of the rectifier diodes along with the 3300uFd filter caps on the power supply board and they all test okay. There is no audio mixed with the buzz. Also, the buzz does not sound like the hum from a bad ground. I'm thinking it may be the output transistors except from my experience that would cause a fuse to blow and the fuses are all good.
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Old 2nd March 2020, 04:35 AM   #4
Enzo is offline Enzo  United States
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Fuses don't always blow, check for DC on the speakers. Look at their cones. When you power on do they move one direction and stay there? if so, that is DC. You can also measure with a volt meter.
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