Roland JC120 Vibrato Problem

[tubby]

Amp works fine and chorus sounds good.
However, when I switch to vibrato it works but sounds very out of tune. "Vibrato Speed" knob works. "Vibrato Depth" knob kicks in from about a quarter turn and doesn´t change much as I turn it all the way.
I did the "checking & adjustment" measurements which are given in the schematic attached on page 1. Actual schematic is on page 2. Supply voltages are in range.
JC120.pdf

Results are in the pics attached. From what I can tell something is definitely off with "chorus adjust" and "bbd out adjust".
I have no idea where to start. Thankful for any help/suggestions!

[Helmholtz]

So vib.depth seems to be stuck at maximum.

Check depth pot and its connections (especially to ground).

[g1]

Results are in the pics attached. From what I can tell something is definitely off with "chorus adjust" and "bbd out adjust".

Scope at R161 for 'chorus adjust' and at R137 for 'bbd out adjust'. There are various versions of schematic so you must be sure you have the right one or those component numbers will not apply.

[tubby]

Scope at R161 for 'chorus adjust' and at R137 for 'bbd out adjust'. There are various versions of schematic so you must be sure you have the right one or those component numbers will not apply.

That's what I've done to get those oscope screen shots attached above. The component numbers fit with p.2 of the schematic linked above.

[g1]

That's what I've done to get those oscope screen shots attached above. The component numbers fit with p.2 of the schematic linked above.

If the first 2 pics are not reversed, you need to adjust your time base as the pic labelled 'chorus adjust' should be around 0.8 Hz and your scope is showing something at about 356 KHz, so maybe just HF noise.

Also, your scope probe may need a tweek for better squarewave response. There is usually a trimpot on the probe, and scopes often have a squarewave cal. pin jack where you plug the probe in to calibrate.

[tubby]

So vib.depth seems to be stuck at maximum.

Check depth pot and its connections (especially to ground).

Good call on the pot! Connections were good, but resistance was all over the place while turning. Will order a new part and replace.
However, the bad pot probably won´t explain the the out-of-tune sounding vibrato, would it?

[tubby]

If the first 2 pics are not reversed, you need to adjust your time base as the pic labelled 'chorus adjust' should be around 0.8 Hz and your scope is showing something at about 356 KHz, so maybe just HF noise.

Also, your scope probe may need a tweek for better squarewave response. There is usually a trimpot on the probe, and scopes often have a squarewave cal. pin jack where you plug the probe in to calibrate.

The pics I´ve attached are labeled. You´ll see the label if you hover or click on a pic.
So, the first pic is the BBD out adj, where going after the service manual I should expect two sine waves of undefined frequency and get them to overlay as close as possible. The screenshot is the actual masurement with as closely aligned curves as possible.
Aligned like that, VR9 is smack bang in the middle, so I think I have the actual signal at that test point, it´s just totally messed up. Should I try and replace IC2 (MN3004)?

My scope probe shows a perfect square wave response on the the cal jack, so pic 2 (chorus adj) seems to be another hint that something is off (it should be a triangle waveform according to the service manual).
Maybe replace IC4 (MC14011BCP) and check the components around it?

[Helmholtz]

Real vibrato (as opposed to tremolo) means frequency or pitch modulation.
A broken depth pot is likely to cause excessive vib depth and thus out-of-tune sound.

[g1]

The pics I´ve attached are labeled. You´ll see the label if you hover or click on a pic.
So, the first pic is the BBD out adj, where going after the service manual I should expect two sine waves of undefined frequency and get them to overlay as close as possible. The screenshot is the actual masurement with as closely aligned curves as possible.
Aligned like that, VR9 is smack bang in the middle, so I think I have the actual signal at that test point, it´s just totally messed up. Should I try and replace IC2 (MN3004)?

Sorry, I got the labels mixed up somehow. Another version of schematic mentions 1Khz in regard to the BBD out waveform. Not sure why the waveforms look so different from the schematic if chorus sounds ok.

As far as I know, the only difference between the 2 effects is that the vibrato is variable and the chorus is fixed settings. Otherwise they both use all the same IC's, etc. so if chorus sounds good, everything is mostly working.
Replace the pot first, see if it corrects the problem.

[tubby]

Real vibrato (as opposed to tremolo) means frequency or pitch modulation.
A broken depth pot is likely to cause excessive vib depth and thus out-of-tune sound.

Replacing the pot did it. Out of tune sound is gone.
Thanks for the help guys!