Roland Jazz Chorus 120 chorus problem

[cg1245]

Hello, I have a Roland jc-120 from the early 80s. When i switch on the vibrato, it works just fine and the adjustments change the speed and depth perfectly, but when I turn on the chorus, it works but I cant adjust it at all. I've tried changing the wiring on the speakers and all it does is just make the chorus and vibrato quiet.

[nevetslab]

Roland JC-120 Schematics

I have two different schematics for the JC120. It may be a supporting op amp that's not working. At lest the two special IC's are working.

It may be that the triangle wave generator isn't running. Here's the two schematics I have for the JC120.

Roland-JC120-JC160 Schematic.pdfroland_jazz_chorus Schematic.pdf

[Jazz P Bass]

I don't recall that you Can change the Chorus.

As far as I know, it's 'fixed'.

[nevetslab]

I don't recall that you Can change the Chorus.

As far as I know, it's 'fixed'.

You're right..... I thought I had recalled the depth being adjustable, but went and looked at the owner's manual, and it clearly states neither the depth nor speed effect the chorus. The Schematics bear that out. Sorry about that.

[cg1245]

thanks, I didn't realize you couldn't adjust it, there is a pot on the back that changes the speed a little though. I was hoping there would be a way to at least adjust the depth.

[nevetslab]

I've never tried to revise the circuit. But, it looks like you could alter the foil pattern from the output of IC5B (pin 7), which presently goes to the Chorus termianl of SW2B, and defeat that, and put the Vib conection there instead...which is the output of the Depth control. Uncharted territory for me...may reduce the intensity of the Chorus too much.

[diydidi]

I Had one where the chorus was weak. The speakers were wired out of phase. Quick fix it was!!