added pictures

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

I think your meter is trying to average the AC voltage on the two inner pins.
Try with the meter set to to Volts AC.

Ok guys sorry for the bo bo 

Anyhow removed the old one (no easy task) and got a new one in

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Seems all is good when measuring the (+) pin and two middle pins (~)

(+) pin reads about 40v DC (have no idea what it is supposed to be


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But when I read the middle pins I get like 16v ac but what the heck I get 20v DC

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I think I'll call it a night

 

Yes sir thanks I was able to find some old pics of the original part

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The rectifier is installed backwards.

Yes sir appears to go to

-negative terminal of capacitor

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-and the emitter of the tip31a on the right

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and a resistor

Follow the trace from the bridge + lead to filter cap.  Is it going to + or - end of cap?

Quote from: markorock37 on April 13, 2024, 02:57:58 PMI don't see 2SA872 on Mouser, is KSA992 a good sub?

Yes, those should work.

Meanwhile... experienced my first Chernobyl.

So this metronome I had removed the bridge rectifier a while back and it tested good...oh well

Put a new one in today.... thought it would be fun to hook my meter to the leads before I clipped em and read ac and DC on the different leads.

So I solder it in...crudely soldered the transformer wires back making sure I put the right ones in order.  Plug it in...I'm gathering up my meter and test leads and I hear woosh and see lots of smoke

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And liquid 

Later I was outside and thinking did I put it in backwards or something...or leave a solder bridge?  But looks like the orientation is correct and the solder reasonable (these pics are post meltdown)

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Im beyond hoping this thing will be fixed but I did want to replace that part.

Meanwhile I put it on my ugly dbt after the fact yes it was glowing.