Roland Jazz chorus with chorus and vib fault

[Arbutt]

Hi
Ive finally hunted down the correct map for this model, With help from you guys. But i feel after a check that i might need some assistance

I have checked all the supply voltages and all seem correct. I can see the vib working at the depth wiper and with the controls change the speed etc
But to be honest i can't work out the rest of the circuit.
Distortion and reverb all ok

If anyone can assist
I would be gratfull
Arbutt

[glebert]

Arbutt, what is the actual fault that you are seeing? You said you can "see" the vibrato working, do you hear it as well? Do you hear anything for chorus? Just an FYI that on the old JC amps the chorus is fixed, there is no adjustment for the depth or speed (this confused the heck out of me for a while when I got mine).

[Arbutt]

Hi thanks . The chorus and the vib are not working. When you flick the switch . It does nothing to the sound . If I go to the wiper of the depth I can see it pulsing up and down . And as you adjust the speed it gets faster. Etc. I just don't understand how the whole thing works. I know you can't control the chorus. Arbutt

[nevetslab]

What are you seeing at the emitter of Q36 on the Effects board? This will have DC on it, whereas the signal leaving this Effects board goes out thru C233, which may not be readily accessible to hook onto with your scope probe. I haven't seen this version of the JC-120, so I see what you're saying with pondering what is going on. We DON'T know what's really going on within the MN3001 & MN3007 chip set that we're used to seeing. I presume this version is earlier than the change to that chip set. The circuit coupling from all of the Chorus/Vibrato is by way of the LED/LDR cell 'PC'. There is a feedback signal from one of the speaker connections down to Q40, leaves via Q39 and onto the inverting input of IC9B and feeds the LED portion of the LED/LDR cell thru R269.

The later models also use a similar feedback path from the Right speaker amp circuit.

[Arbutt]

Hi I will check that tomorrow as it's home time here in the sunny uk. Thanks I will tomorrow

[Arbutt]

Hi . I have checked q36
Base -0.65
Collector 12v
Emitter -0.12v
With the scope on emitter/ c233 I can't see any signal .
Going to ic 6 ..m3002 I can see my signal at pin 3 but nothing at pin 13-14 . Unsure if there is some sort of control via cp1 cp2
There is a feedback signal at r252
At wiper on depth I can on my scope that the trace is going up and down. And can control with speed and depth controls
I hope this can help
Arbutt

[Jazz P Bass]

"Unsure if there is some sort of control via cp1 cp2"

You should see CP1 & CP2 toggle. (IC 7).
This is the 'clock' pulse.

If you have input signal & pin 1 (cp1) & pin 12 (cp2) have a count pulse but you have no output (pin 13/14), then the IC is bad.

Good luck finding one as they have not been manufactured in a while.

[Arbutt]

Thanks . I will check later. I don't remember seeing anything on cp1 or cp2. But I will confirm tomorrow .

[Jazz P Bass]

IC 7 is a dual flip flop ic.

It is set to run as a clock pulse.

The clock pulses are what shift the BBD down the line.

[Arbutt]

Morning. I have scoped cp1 and cp2 . Nothing on them .
Ic8 tc4011 has
Pin 1 -2 -14v
Pin 3 -12= 8v
Pin 4-5-6-9-10-13-14 =14v

Tc4013
Pin 3-4-6-7 = -14v

Ic9
Pin 1 and 7 can see a pulse on the scope which is controlled by speed and depth

Many thanks for the help on this
A

[Arbutt]

Hi. I'm still stuck on this if anyone can assist I would truly grateful . Many thanks arbutt

[nevetslab]

Not having this version of the JC120 in our inventory, I can't look at our unit for comparison. I do see information available on the MN3002 512 stage bucket brigade IC on line. The 4013 Dual Flip Flop should be readily available. You'll no doubt have to track down the MN3002 on ebay or other parts vendors that are affordable. Never tried to find one of those, so not sure how rare it is. I'd swap those two out next, and see if that restores order.

Anyone else have a better suggestion?

[Arbutt]

Thanks netevslap I was thinking of ordering the tc4013 -4011 chips . I will fit and update. A

[Arbutt]

Many thanks job finished now. Replaced tc4013 and tc4011 all working .
Arbutt