Boss CE-1 weird out of pitch chorus sound, trim pot, bucket brigade IC (video)

[Farrell]

Our Boss CE-1 goes unusually out of tune whenever the chorus is dialled up, here's a video of our pedal:

https://www.youtube.com/watch?v=KYVR1jdgQVQ

As you can hear the chorus wobbles a lot more out of tune than it should, a working Boss CE-1 or CE-2 (or any good chorus) doesn't do this.

A working Boss CE-1:

https://www.youtube.com/watch?v=VnW-FJsalTA

Our tech says the trim pot appears to be "stuck" in the middle setting (probably where it should be though?) and there seems to be a failure with the MD3002 bucket brigade delay IC.  However we've not found a way to get the CE-1 to work properly yet.  The vibrato function seems to be working perfectly, only the chorus function is malfunctioning.

Thanks in advance for your advice!

[Scruffie]

"Our pedal" 

Best guess, problem seems to be in the LFO or Multi-vibrator, perhaps a dry electro on a pedal this age but you need to follow this - http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

[Farrell]

Shared between a guitar player and keyboardist 

So you don't think it's a faulty MD3002 (as suggested by our tech) based on the video?  Chorus=too pitchy, but vibrato works fine.

Will check out the debugging link, cheers.

[Scruffie]

Ahh okay 

Nope, I don't think it's a bad MN3002, they usually get suspected due to being the most expensive part and 'heart' of the circuit but the fact your vibrato works tells us it's fine, you'd have symptoms there too if it was damaged.

Now, something that supplies the MN3002 and tells it how to work, that'd cause your issue.

A tech that fiddles with trimmers without knowing what they're for perhaps isn't the best person to have poking around... assuming the schematic i'm looking at is correct there's only one trim and it's for clock cancellation and it's probably fixed in to position to prevent user adjustment after being factory set, now that might have gone out over the years but it's unlikely to be related to the current issue.

[ElectricDruid]

Definitely sounds like the LFO to me too.

There's a certain "jumpy" quality to it, which makes me think the LFO might not be outputting the typical triangle/sine wave but instead something more squarewavey. But the Vibrato uses the same LFO, and you say that seems to be ok, so that would rule that out.
Perhaps the LFO has moved so far off its usual bias point that it's cutting off for much of the time. I suppose that symptom could be caused by something in the clock VCO's modulation circuitry going AWOL as well as the LFO itself.
Alternatively, it could be the LFO level being much too big for Chorus. I notice there's a "depth" pot for vibrato whic doesn't affect the chorus. The voltage divider that sets the level could be dead (R78 / R79? on the schematic I found) A cracked joint or dead resistor on the lower of the pair could give much too much signal to the VCO and give the effect you're hearing.

I'd want to get a oscilloscope on the LFO and see what was going on. If that's ok, move on to the divider, then the clock VCO. Almost certainly it's *not* the BBD, that much is for sure.

HTH,
Tom

[anotherjim]

+1 Tom ^
Haven't got time to listen to the clips, but, getting chorus at all depends on the delayed and clean signals being mixed. If not mixed you have either clean or vibrato.
I think this circuit does the mixing via the output jacks? It could just be that the "second" output jack provided for a stereo effect contains a switch contact which directs the effect to the "mono" output WHEN no plug is inserted in the "stereo" jack.
A bad/dirty contact in the "stereo" jack socket could cause this trouble?

[Farrell]

Thanks for all the advice.  I spoke to our tech with all these advice in mind, then he responded with this

"I have a sine wave from the LFO in Vibrato mode, but no square or triangular wave form in chorus,changed resistors ic,and capacitor, no difference..." 

Then later:  "Think I solved it...the first TA 7136 ic was outputting 8 volts dc and very noisy! this was upsetting the dc from IC 3.
couldn't source a cheap TA 7136 so i've made a dual in line to single in line convertor and used a different ic[just as good]."

However when we tested the CE-1 again it still sounded too pitchy, as documented below:

https://youtu.be/srDiQY-YMSU
https://youtu.be/uQg3wbOYKyg

CE-2 comparison, same amp chain (Boss CE-2 > Binson Echorec > Fender Dual Showman Reverb)

https://youtu.be/Mz0n2E2btNg

Any thoughts?

Thanks again!