Roland JC 50

[J Ruiz]

Hello, new to group. Having a dead chorus & vibrato on a jc 50. I just hit a wall with it.

[Jazz P Bass]

Is the wall alright?

[DrGonz78]

Anything already posted here help at all?
http://music-electronics-forum.com/t37939/

[J Ruiz]

Actually i read those, and copied the schematic but, it is not exactly the same. There are differences on the circuit and , i am still dealing with the problem. Thank you any ways.

[Jazz P Bass]

So what exactly is the problem that you are having with the amp?

Here is the 1979 schematic: Roland JC 50 schematic '79.zip

[J Ruiz]

The chorus & vibrato effects are not working and i cant find the problem even, after replacing the efects I Cs.

[Enzo]

ALL the FX ICs?

it may not be an IC that is bad. Start with the vibrato. Lower right, Q26,27,28 are the oscillator. Is there an oscillator signal at the depth control?

IC2 is the clock IC, is there a clock pulse at pin 3, and are there CP1 and CP2 coming out pins 1 and 2? Those are clock pulses for the chorus IC, IC5 lower left.

Up top along the signal path, to the right of Q3 is an arrow pointing to a circled X, this next to C10. That X signal is the feed from the main signal path down into the chorus section. Which is lower left, through C50 into Q21. So is there signal leaving Q21 and Q22? Is the signal leaving IC5? Does it make it through Q23,24,25? From there fed back into the signal path via Q17. Is the gate of Q17 off so it will conduct?

left of the speaker is IC4, below which is an LED marked PH. That is half a photocell. The other half is back down by IC5, it is that resistor in a box under C58 near the base of Q23. The output to the speaker is sent through Q20 and Q28 to ultimately drive that LED, so is that happening?

[oc disorder]

Are all the switch contacts working ok ? I seem to remember a problem with a switch on those.

[J Ruiz]

The switch seems to work, i check for continuity.