Boss CE-2 weird loud electrical noise when off

[Golgoth]

I've been given a vintage Boss CE-2 pedal that was not working. I fixed the chorus part that was not working by brute-forcing the repair, replaced all four chips and polar caps.

Still remaining is a strange issue that was present when I got the unit. When the pedal is switched-off (and only off) + has the power supply plugged, there is a very strange and loud "electrical" or "static" intermitent noise coming out of the pedal.

Struggling to narrow down or isolate the issue, could this be related to the JFET switching part and maybe to a grounding problem somewhere?

The pedal does not have the battery in, has the 9V mod to be able to use a standard 9V PSU and is plugged to a known good PSU usually powering other vintage Boss pedals with no issues.

 

[CJ]

Q9 would be on my list of main offenders.

Wiring for tru-bypass is a pain with that switch setup.

Nice chorus, I got two of them, MIJ 80's.
You can play with that pot for the best sound.
Trick to those is to turn the rate all the way off.

Xvive does a reissue mn3007,

 

[RoadrunnerOZ]

I don’t think the schematic you have is quite right with the power connection.

 

[Golgoth]

Q9 would be on my list of main offenders.

Wiring for tru-bypass is a pain with that switch setup.

Nice chorus, I got two of them, MIJ 80's.
You can play with that pot for the best sound.
Trick to those is to turn the rate all the way off.

Xvive does a reissue mn3007,

Thanks CJ, will try and replace Q9! Did not occur to me to pinpoint to the bypass connection.
I love that chorus too! Working beautifully when engaged. I hope to get it in better overall shape soon!

 

[Tubetec]

Ive done experiments with dual Boss CE-5's ,
reproducing the CE-5 outputs over a set of monitors ,with the direct guitar pickup signal coming from the amp , by controling the frequency and relative position of the LFO wave in each pedal you can generate a sort of ping pong chorus , so first the direct signal arrives via the amp then the chorus's panned, arrive some mSeconds later , its three discrete sound sources that mix in physical space , it adds a lot of width and timbre to the otherwise hole in the head mono signal you get from a pickup .
Add in some tails from spring tank reverb and your sitting in a very immersive space ,

I tried it out on a few guitar picker friends , they got that glazed, out to lunch look in their eye and drifted off for 15-20 minutes , noodling with all analog psychoacoustic processing .

 

[Golgoth]

Q9 would be on my list of main offenders.

Wiring for tru-bypass is a pain with that switch setup.

Nice chorus, I got two of them, MIJ 80's.
You can play with that pot for the best sound.
Trick to those is to turn the rate all the way off.

Xvive does a reissue mn3007,

I replaced Q9 without success, same issue.

I removed R22 to take the BBD and LFO out of circuit, no more noise. Does that narrows down the issue to this part of the circuit?

Thanks!

 

[RoadrunnerOZ]

Could be the diode D4 or one of the transistors in the flip-flop. First I’d go over the board with a soldering iron and fresh solder.

 

[JohnRoberts]

Just to be clear... pedal is switched off but power still connected?

If the FF generating the gate drive to Q9 is not stable/quiet, that could be a source of noise partially switching the JFET on.

JR

 

[RoadrunnerOZ]

Looks like. And no battery installed.

When the pedal is switched-off (and only off) + has the power supply plugged, there is a very strange and loud "electrical" or "static" intermitent noise coming out of the pedal.

 

[CJ]

i would not touch up any solder joints unless you have to- chance of making matters worse with a solder bridge,

how is the LED? brite enuff? a common mod is to drop the series resistor down to brighten it up,

you have a scope? might have to track the noise down with a scope,

 

[RoadrunnerOZ]

It’s not like smd - it’s all through hole and wide solder pad spacing - with a fine tip and solder and a magnifier, as long as you’re careful it’s pretty easy to resolder. I fix a lot of FX pedals and they do start to suffer bad joints with heat in an enclosed box - especially the older ones like Mu-Tron etc. or some tube OD pedals.

 

[Golgoth]

Could be the diode D4 or one of the transistors in the flip-flop. First I’d go over the board with a soldering iron and fresh solder.

Hi, I removed R22 and the noise is not there anymore. I guess that would exclude the JFET circuit from being the culprit correct?
Now that the chorus part of the circuit is disconnected and the noise gone I feel like this is a good place to start looking at.

Let me know if I'm overlooking something here!

 

[Golgoth]

Just to be clear... pedal is switched off but power still connected?

If the FF generating the gate drive to Q9 is not stable/quiet, that could be a source of noise partially switching the JFET on.

JR

Absolutely, power cable still plugged in!

FF meaning the chorus part of the circuit?

 

[Golgoth]

i would not touch up any solder joints unless you have to- chance of making matters worse with a solder bridge,

how is the LED? brite enuff? a common mod is to drop the series resistor down to brighten it up,

you have a scope? might have to track the noise down with a scope,

The LED is doing great, will try to get my hands on a scope for investigating!

 

[RoadrunnerOZ]

Absolutely, power cable still plugged in!

FF meaning the chorus part of the circuit?

FF is Flip-Flop - Q6 - Q7 -this is the switch controller for Q9

 

[RoadrunnerOZ]

If the Flip-Flop is noisy it will cause Q9 to behave erratically. Removing R22 just disconnects power to Q9 - which means that if the source of noise is the Flip-Flop (or LED transistor Q8) you won’t hear the noise.

 

[Golgoth]

If the Flip-Flop is noisy it will cause Q9 to behave erratically. Removing R22 just disconnects power to Q9 - which means that if the source of noise is the Flip-Flop (or LED transistor Q8) you won’t hear the noise.

That makes more sense!

 

[CJ]

You could reconnect r22 and pull the led transistor and check noise,

Did you try messing with the trim pot?

 

[Golgoth]

You could reconnect r22 and pull the led transistor and check noise,

Did you try messing with the trim pot?

Hi,

I finally got some free time to get back to work on the pedal. The situation has changed and the issue is now present when the pedal is powered on.

Here is the current situation, as I had many spare parts and thought it would be an easy fix, I tried the following:

- Electrolytics were all replaced
- Diodes were all replaced
- Transistors were all replaced
- ICs were all replaced
- Potentiometers were taken out of circuit, cleaned and checked
- All solder joints reflowed
- Power is fine at ICs inputs, ICs were tested in diode mode and no shorts were found
- Audio is passing through and coming out at -39db compared to the input
- No chorus effect, but rate clicks and depth can be heard when pots turned
- Currently D4 is disconnected to let the flip flop out of the equation, is having Q9’s gate leg floating an issue?

The pedal is barely passing audio, no effect can be heard, and there is a very loud noise at the output and many points in the circuit, most of them located around TL022 and the output jack, as detailed below:

Noise sample:
http://sndup.net/bcsx

Noise locations findings using audio probe:
- Pin 5 -> C17 (replaced) -> R25 (no noise on either of R26 pins)
- Pin 6 -> R31 (replaced)
- Pin 8 -> R30 (replaced, highest noise point in the circuit)
- Pin 10 -> R32 (replaced) -> TL022 pin2 (IC was replaced, checked for shorts and seems healthy)
- Pin 11 -> C19 (measures .1uF correctly)

I am out of ideas here I hope the details might point to something I have been missing perhaps!

Thanks!

 

[Golgoth]

I don’t think the schematic you have is quite right with the power connection.
View attachment 120675

That scheme is indeed the correct one and has been very helpful since I got back to investigating, thanks a lot for posting! I added some details in the post above!