JC120 chorus problem

[acorkos]

I'm not sure which version this is....looks like an early one, though. trying to find the right schematic.

vibrato works normally, speed and depth knobs do what they are supposed to. switch over to chorus....depth seems to work ok, but speed control does nothing. only a slow speed chorus regardless of where the speed knob is set. there's a chorus adjustment knob on the back panel and a trim pot on the PCB, but neither does anything to speed up the chorus effect. any ideas of what might be wrong and where i should start looking? thanks!

[acorkos]

here's what i think i am looking at...

[Enzo]

What is your serial number, the schematics usually indicate the serial number range.

[acorkos]

960xxx

[52 Bill]

I know that this has come up before, if you look at the schematic, the speed control only is connected when the vibrato is turned on. The chorus speed is preset and does not change with the speed control.

[teemuk]

I know that this has come up before, if you look at the schematic, the speed control only is connected when the vibrato is turned on. The chorus speed is preset and does not change with the speed control.

Unless it's a pre '82 model, in which case it's totally different, likely having two separate LFOs for chorus and vibrato and possibly even a "hidden" potentiometer for chorus adjustment.

It is absolutely mandatory to find the right schematic that matches the exact version of the amp you have. These things vary A LOT.

[Alex R]

...what 52Bill said. That speed control is confusing but it is just for the vibrato on every one of these I've ever seen.