Troubleshooting a Boss CE-2

[stoneattic]

I have a Boss CE-2 that just stopped "chorusing". It passes signal fine but there is no effect. I used an audio probe to determine that the audio is making it to the BBD and out of the BBD. It seems to me that if the audio is making it though the BBD then the BBD must be okay and 'm guessing that the FLO isn't oscillating.

So how do I test the LFO?
Or could I be missing something else?

Thanks!

[The Dude]

Posting for reference:

[Mark Hammer]

The majority of commercial pedals that produce their effect by combining a dry and modulated signal typically do their bypass switching by cancelling the modulated part such that only the dry signal remains.

If they use electronic switching (which most will), that means the flip-flop circuit turns a single lonely JFET on and off. In the CE-2 that will be Q9.

Those JFETs are not especially fragile, but they have been known to partially or fully fail. So, you may hear some people noting that their Boss pedal bleeds effect when in bypass mode, and things of that order. The flip-flop circuitry works fine, and the LED lights properly, but the effective bypassing and engagement of the circuit is wonky.

You can check to see if Q9 is preventing the delayed signal from making it to the mixing stage by simply bypassing it with a little piece of wire. Identify Q9 on the board, identify R22, and find pin 2 of IC1. Scrape a little of the green lacquer covering the pads off and temporarily solder a short piece of wire between the transistor side of R22 and the nearest connection to pin 2. In theory, that will make the chorus effect "on" all the time, and independent of footswitch action.

If your pedal behaves as I've described, then Q9 is your problem. Remove the wire bridge, and replace Q9 with a suitable JFET.

[stoneattic]

Thanks for the responses, and sorry for the delay getting back to this.

I jumpered past Q9 with no obvious change in function. It passes signal through but there is no chorus effect.

Next I audio probed the signal path using my homemade probe (Simple Circuit Debugging). I get audio all the way through the MN3007 and up to R22, but nothing past (though) R22. I measure 47K though R22 and the traces past so it seems like the resistor is good. This has me somewhat confused.

All of the probed audio sounds like there is no chorus effect. I wasn’t sure if I would be able to tell without the original signal there too so I took the audio from the probe and “Y”ed it in with the original signal and still hear no chorus effect.

Also, nothing I do with the Rate or Depth settings has any effect on the probed or “Y”ed signal.
Any thoughts?

[52 Bill]

Also, nothing I do with the Rate or Depth settings has any effect on the probed or “Y”ed signal.
Any thoughts?

Remember that the MN3007 chip needs to be controlled by the clock pulses from IC3 and from IC2 for the delay to take effect. Check IC2 to see that the oscillator is running and if you have access to an oscilloscope check the outputs from IC4.

[stoneattic]

Remember that the MN3007 chip needs to be controlled by the clock pulses from IC3 and from IC2 for the delay to take effect. Check IC2 to see that the oscillator is running and if you have access to an oscilloscope check the outputs from IC4.

The MN3007 is IC3. Did you mean IC2 and IC4?
I was thinking along those lines since the MN3007 was passing signal, but I don't know what to check for on IC2. Do I just check for a voltage coming out of pin 1 that varies with Rate and Depth? I do have an old O-scope but don't know what I'm doing with it enough yet to see what output the MN3101 is sending.

[52 Bill]

The MN3007 is IC3. Did you mean IC2 and IC4?
I was thinking along those lines since the MN3007 was passing signal, but I don't know what to check for on IC2. Do I just check for a voltage coming out of pin 1 that varies with Rate and Depth? I do have an old O-scope but don't know what I'm doing with it enough yet to see what output the MN3101 is sending.

Yes, my error on the ic numbers.

IC2 is the LFO (low freq osc). There should be a changing voltage that is controlled by the speed and depth controls going to Q4.

There should be two, out of phase clock signals from pins 2 and 4 of IC4 that feed the delay chip.

[stoneattic]

Yes, my error on the ic numbers.

IC2 is the LFO (low freq osc). There should be a changing voltage that is controlled by the speed and depth controls going to Q4.

There should be two, out of phase clock signals from pins 2 and 4 of IC4 that feed the delay chip.

I finally got a chance to look at this again. When measuring with my DMM set to Vdc I get a steady +5V on both pins 2 & 4 of IC4 regardless of RATE and DEPTH settings.

So I measured the inputs to IC4 on pins 5 & 7 and get 0.34Vdc and 3.44Vdc respectively regardless of RATE and Depth settings.

So going back further I measured the output on DEPTH pot feeding Q4 and depending on the RATE and DEPTH settings can get a slight change in output from 4.55Vdc to 4.99Vdc. It seems to me this should be a bigger range. Could this point to IC2 being bad, or is that small range typical?

BTW. I do have 9+ Vdc on the power inputs of IC2, IC3 and IC4.

[52 Bill]

So going back further I measured the output on DEPTH pot feeding Q4 and depending on the RATE and DEPTH settings can get a slight change in output from 4.55Vdc to 4.99Vdc. It seems to me this should be a bigger range. Could this point to IC2 being bad, or is that small range typical?

BTW. I do have 9+ Vdc on the power inputs of IC2, IC3 and IC4.

Does the voltage on the depth pot fluctuate (rise and fall) or just change from 4.55 to 4.99 volts when you move the pots?

Is the bias voltage okay?

[stoneattic]

Does the voltage on the depth pot fluctuate (rise and fall) or just change from 4.55 to 4.99 volts when you move the pots?

Is the bias voltage okay?

The voltage on the DEPTH pot only changes from 4.55 to 4.99V when I move the DEPTH and RATE pots. Otherwise it holds steady.

Where would I measure the bias voltage?

[52 Bill]

The voltage on the DEPTH pot only changes from 4.55 to 4.99V when I move the DEPTH and RATE pots. Otherwise it holds steady.

Where would I measure the bias voltage?

Are you reading the voltage at the wiper of the depth pot?

One end of the depth pot connects to the bias voltage (1/2 V+ or about 4.5vdc) from the junction of R33 and R34, which I guess you have. If the LFO is not running, test the components and connections around IC2. If all tests okay, then replace IC2.

[stoneattic]

Are you reading the voltage at the wiper of the depth pot?

One end of the depth pot connects to the bias voltage (1/2 V+ or about 4.5vdc) from the junction of R33 and R34, which I guess you have. If the LFO is not running, test the components and connections around IC2. If all tests okay, then replace IC2.

Yes, I'm reading the voltage (4.55 to 4.99V) at the wiper.

I read 4.75V for the bias.

I assume I need to pull the components to measure them? We're talking R29 through R32 and C19, correct?

Thanks!

[52 Bill]

I assume I need to pull the components to measure them? We're talking R29 through R32 and C19, correct?

I always test in circuit and only pull one end if I can't get a normal reading.

[gearhead63]

Here's a Boss service Note on that unit. Not sure it will help.
Here's a site that has a bunch of BOSS Service Notes and schematics.
Boss -Service Manual Download|Circuit Download|Download Drawings|schematic download|route map download|free download user manual

[stoneattic]

SOLVED!

It was the TL022, but not the IC itself. I measured the components around it as suggested by 52 Bill and found they were all good (or at least close). So I went to pull the TL022 and as I was de-soldering I noticed that one of the pin solders appeared cracked (pin 5 if I remember correctly). I had looked for bad joints early on in my troubleshooting but did not see it then. I should have know better and just re-flowed all the joints but didn't. Since I was already mostly done de-soldering I finished pulling the TL022 and put a socket in. I put a TL082 I had laying around in and had chorus again! I then put the original TL022 in the socket and had chorus. So in the long run it was probably a bad joint that I either missed initially or make worse fiddling with things to the point I could see.

Thanks for pointing me in the right area and explaining everything!