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Old 10th November 2012, 11:26 AM   #1
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Default Roland Jazz Chorus 77

Dear All,

friend of mine gave me a Roland Jazz Chorus 77 for fixing some problem.

First problem : there is an udible 50 Hz coming form the speaker.
Second problem : A high frequency noise is udible.
Third problem : by rotating the front knob some noise is udible.

Now I'm looking for electric schematic of the JC 77.
Also I ask for some suggestion regarding the repair.

I believe the firs problem is related to the two electrolitic capacitor on the power supply. Or not ? Any suggestion is really appreciate.

No idea about the second problem.

The third problem is related to the potentiometer. They are shielded components but I suppose the dust went in. Can I solve with specific spray or do I need to change all ?

Please, really any suggestion and help for the schematic is realli appreciate.
Volturnofelix
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Old 11th November 2012, 08:17 PM   #2
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Electrolytic capacitors over twenty years old are always suspicious, in my opinion. This may be ROHS compatible and the silver solder may be difficult to remove. I had to pry the caps out of a computer mainboard recently, then drill the remaining solder out with a pin vise. Wouldn't suck out.
Cleaning pots with contact cleaner is a usual first step. Use the aliphatic hydrocarbon forumula, not the plastic melting brominated hydrocarbon formula sold at factory supply houses. Warning contact cleaner is flammable, no smoking, open flame, electricity turned on or off within 10m. Set up a fan before spraying to dissipate the fumes.
You may find more Roland experts in the electronics forum of organforum.com. This is not quite an organ, but there are some servicemen there with roland franchises.
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Old 11th November 2012, 09:58 PM   #3
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all good wisdom
on the matter of cleaning controls if cleaning doesn't clear up the grief it may well have worn or broken controls
i think i might have a schematic for a Jazz Chorus 70 i can't say how much different it is to the 77?
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Old 13th November 2012, 06:13 PM   #4
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Dear Indianajo and Turk 182, thank you for your reply and help.
As first step i'll replace the capacitor by following your suggestion in removing solder.
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Old 24th November 2013, 01:26 PM   #5
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any luck?
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Old 29th November 2013, 04:38 PM   #6
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Yes, I replaced the capacitors on the power supply and clean the pots. Now it's working fine.
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Old 1st December 2013, 01:29 AM   #7
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Thanks for reporting back. I have an admistrator on another website giving me bad reviews because I suggested a 30 year old digital synthesis organ with an annoying buzzing sound should have had the amp caps and other electrolytic caps replaced before the tech replaced two entire PC boards. The PCB's are factory stock and fairly expensive. Oh, BTW, the power amps were replaced a year ago with amps that were only 20 years old, by the same tech. I did say something about the possibility that the speakers were also the problem, and should have been checked.
The customer this fall scrapped the organ.
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Last edited by indianajo; 1st December 2013 at 01:49 AM.
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