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June 16, 2024, 03:15:55 PM

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Jazz Chorus 60 repair

Started by LMW93, April 14, 2024, 12:51:02 PM

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LMW93

Hello everyone!

I recently got a broken Roland Jazz Chorus 60 for cheap. It seems to be a pretty early model, because I couldn't find any similar ones by searching the web (pictures added). The previous owner told me that it stopped working like 20 years ago and that a friend of him tried to fix it with no results. two or three components are missing with burn marks on the circuitboard. Could be normal- or the fusing-resistors I think. I think he tried to exchange them, without changing the actual problem so he burned the circuitboard. I think it should be an easy fix to retrace the little burned parts of the circuitboard. But my problem is that I can not identify the missing components cause I'm not very good in reading schematics and identify the traces on the circuitboard.
The main problems which caused the components to burn out, are probably the old transistors so I ordered new ones.
for the 2SC1628Y I ordered a SC3503 and for the 2SA814 and the 2SC1624Y I ordered a MJE15030 and a MJE15031.
now my question is: has anyone seen this version of the Roland JC-60 and can identify the missing parts? and are the ordered transistors the correct replacement?

I've added pictures of the amp and the circuitboard plus a schematic for a different version of the JC-60, which seems ok for the power amp circuit.

thank you!









https://ibb.co/W6ZC157

LMW93


saturated

Wow nice amp  :)

Welcome to the forum

 8)
I ask stupid questions
and make stupid mistakes

criticism, critique, derision, flaming, verbal abuse welcome

g1

The service manuals usually go by serial number, what is it?

LMW93


LMW93

#5
Quote from: g1 on April 14, 2024, 02:44:32 PMThe service manuals usually go by serial number, what is it?
The serial number of the amp is #430830.
In the service manual is a note that for the JC-60 its for #787100- and for the JC-60A R&P its for #810530-. It was first printed on March 31. 1979 and its the fourth edition.
The amp is a earlier version, it has a different circuit board, different power transistors and has less control inputs on the back. i couldn't find the right service manual for my version. just the one mentioned and newer ones.
Does anyone maybe have an earlier service manual?

Jazz P Bass

Your serial number indicates a manufacture date of June of 1975.
The schematics that you found are from 78 & 79.

LMW93

Quote from: Jazz P Bass on April 15, 2024, 10:56:14 AMYour serial number indicates a manufacture date of June of 1975.
The schematics that you found are from 78 & 79.
Thank you for the info about the manufacture date! Seems to be the first version of the JC-60 then. I read somewhere that they started building the jc-120 and the jc-60 in 1975.

LMW93

ok i found an older service manual for the jc-60 #512400 (and higher) from june 1977.
it even includes a wiring diagram and a components layout for the jc-60 #481650-#502399, but it's still not the right version.
Does anyone have an idea where I can find the correct version?

Tassieviking

Have a look at the last layout for the JC-120, it shows the layout of the same PCB I think.
The JC-120 appears to be 2 lots of JC-60 amps in one box.
This is the closest I have on that amp.
There are no stupid questions.
There are only stupid mistakes.

LMW93

Quote from: Tassieviking on April 15, 2024, 02:49:34 PMHave a look at the last layout for the JC-120, it shows the layout of the same PCB I think.
The JC-120 appears to be 2 lots of JC-60 amps in one box.
This is the closest I have on that amp.
Perfect, thank you!
i'm going to check the values of the components and compare them to the ones on my jc-60 later to verrify that, but the layout seems identical.
Thank you a lot!