Help with CE-2 pedal

[Matoni]

Hello,
I need help with my Cepheid Chorus build. I am getting a signal coming through when I plug the pedal in, but there is no chorus sound. This is probably because of the R34 47K leak resistor seen at the very top of the schematic. There is no chorus sound, however. I have probed with an oscilloscope, so I know that there is a signal going into the MN3207 chip I am using, as well as voltage going in the correct pins, however, there is no signal coming out of pin 7 or 8. Please let me know what tests I can run to try and further diagnose the problem. I am using a corresponding MN3102 clock chip, but it may not be working. I have no clue how either the BBD or Clock chip work. Please let me know what I may have done wrong. I will post pictures if they are requested. Thanks so much in advance for your help.

 

[Matoni]

just clipped that leg, doesn't fix it. I didn't think it would but thank you for making me clip that, it definitely was too close for comfort.

 

[Matoni]

new BBD and clock are ordered and on their way. I got the ones Robert recommended. Hopefully, this is the issue. Tell me in the mean time if there is anything else that looks bad on the board.

 

[Mcknib]

Maybe time for a wee recap

I can't remember everything I've asked

You've got clean signal going all the way to the mixer stage IC2.2

Your LFO output pin IC1 voltage fluctuates

Post IC3 and 4 and Q3 base voltage as they are now check Q4 base voltages with the depth pot fully up and fully down

Try cranking the bias voltage up to 5v

 

[Matoni]

Everything you said is correct. The LFO does appear to be working, as indicated by the LFO LED. The voltages on Q4 are a little bit strange. the base (middle pin) doesn't change when I turn the depth pot fully up and down. Is this a problem? the voltages here are also extremely low, and I' dont think they are supposed to be. The voltages off Q4 are as follows: pin 1: 0vdc, pin 2: 0.6vdc, pin 3L (this is very strange as this should be directly connected to voltage): 20mvdc. Maybe something is wrong with R25, the 2.7k resistor bringing voltage to the transistor. Or maybe this is caused by it being directly attached to the chip. Either way, i think I might try and change out this resistor to see if it changes anything. Let me know if I should try that and what other measurements I should try. My hope is that it is just a simple chip problem and the new chips I ordered should take care of it. Hopefully... not sure though. Thanks again for all the time and effort all you guys are putting in to helping me fix this pedal. I am only 15 and so I am a relatively new builder, so all of these debugging techniques will help me in the future. Thanks so much.

 

[Mcknib]

Check the voltage both sides of R25 first

You're correct you will learn a lot debugging even though it's frustrating I always try to look at it as learning new stuff

 

[Matoni]

One side is 8,6vdc and the other side is 20mvdc. I changed out the resistor anyways, and it didn't fix anything. so I still have no clue what the problem is. if you look at the picture of the bottom of the board I sent, right by R25 there is a small bit of exposed copper from the board that must have been burned off by the soldering iron or something like that. Maybe this is part of what is causing the problem? maybe something is shorting? I have no clue. Let me know if you think that is a problem.

 

[Mcknib]

Lift the low voltage side of the resistor out and try soldering that resistor leg directly to D4 cathode

In fact D4 cathode solder joint looks dry try reflowing that first

 

[Matoni]

I used solder to bridge the two legs together. It doesn't create any difference in the sound I am getting out of the unit. Is the low voltage correct or should it be higher? Im not completely sure what it should be at. Thanks again for all of your time and effort on this project I really appreciate it.

 

[Bio77]

Don't use a solder bridge. Try the D4 reflow with more solder, if nothing, pull the legs out and connect. If you have bare copper, the solder bridge is going to connect the components to ground.

Did you bend the leads down and cut them with clippers before soldering? That's usually fine, in fact, its the way I do all of my builds. I'm asking because, I did this once with some very sharp snips and I ended up removing the solder mask (when I snipped) and I grounded a bunch of components. Your comment on the bare copper made me think of that.

 

[Matoni]

no, i bridged it on top not on the bottom with the bare copper. And yeah I think that's what happened.

 

[Mcknib]

Yes I'd think with a 2K7 you wouldn't drop that much voltage but I'm no expert with this circuit according to the electrosmash article it's set up as an astable

Continuity check that part of the circuit put your probes on the component legs/pins rather than solder joints make sure it's all connected as it should be

Hopefully you'll be lucky with your new ICs

For further learning you could check resistance using the schematic if you look at resistance between +9v and Q4 collector (pin 1) you can see you should get 2K7

With no power to the circuit check your resistance from any +9v to Q4 collector

You can use this method for finding bridges, shorts, open circuit etc basically look at a particular trace and use a reference point in this case +9v to check resistances along that trace / path if it's not as expected e.g. infinite you know you've got an open circuit or bad connection and so on

Obviously in some cases you'd need to take into account paralell resistance etc

Now I'm not always sure if other resistances would be added if you take for example resistance between IC2.1 pins 1 and 2 I'd say 47K (R14) but I don't know if R9 and 10 would affect resistance

Try it and let me know!

I just do the easy stuff VREF to pin 3 = 10K if it ain't 10K there's a problem between VREF and pin 3

 

[Matoni]

just measured all the spots you recommended to measure with my DMM. R25 does measure at 2.7K, so I have no idea why the voltage drop-off is so huge. FYI, the other resistor values don't affect the value of R14, and R14 measures at the correct 47K.

 

[Mcknib]

Use your scope to see if you get a triangular waveform at lug 2 of the depth pot some info here

The chorus effect: origin, and working of the Boss CE-2 | Anasounds

Addict to te sound of analog chorus? We talk about it right here! Back to the origins and the working principle of the chorus effect.

anasounds.com

I'm not sure on the workings of Q4 but reading the brief description on the electrosmash analysis it's described as an RC astable oscillator so could vary transistor voltage depending on it's state

Edit I should add this is just for info and learning + checking all the circuitry around the clock and BBD, as you read the articles you'll see it's all interconnected and if one bit doesn't work it'll have a knock on effect

 

[Matoni]

yes I do have triangular wave forms after the depth pot. This is the first time i've scoped for these waves, and it certainly is cool to see.

 

[Mcknib]

yes I do have triangular wave forms after the depth pot. This is the first time i've scoped for these waves, and it certainly is cool to see.

Yeah it's interesting reading about the circuit and seeing it for yourself

Another useful exercise is to remove the clock in this case from it's socket and see what the voltages are on the empty socket and compare them to voltages taken with the IC in socket

This will sometimes indicate the IC is indeed kaput you can see from the schematic where you'd get signal regardless of whether the ICs in or not

Looking at the clock you'd expect signal on pins 5 and 7 with the 9v connection to Q4 try that and see if there's any difference to the voltages on those pins

For your own learning and amusement you should look at the waveform from the rate pot middle lug and turn the pot up and down to see how it changes it

You can also check with your scope if the signal to the base (pin 2) of Q2 changes as you turn the depth pot from one extreme to the other

 

[zgrav]

Yeah it's interesting reading about the circuit and seeing it for yourself

Another useful exercise is to remove the clock in this case from it's socket and see what the voltages are on the empty socket and compare them to voltages taken with the IC in socket

This will sometimes indicate the IC is indeed kaput you can see from the schematic where you'd get signal regardless of whether the ICs in or not

Looking at the clock you'd expect signal on pins 5 and 7 with the 9v connection to Q4 try that and see if there's any difference to the voltages on those pins

For your own learning and amusement you should look at the waveform from the rate pot middle lug and turn the pot up and down to see how it changes it

You can also check with your scope if the signal to the base (pin 2) of Q2 changes as you turn the depth pot from one extreme to the other

Lots of good suggestions in those posts for learning and getting more understanding for troubleshooting.

 

[zgrav]

also -- after you improved your voltage reading, did you try the trim pot for the BBD again? probably a good idea to keep checking that after any changes you are making that might be restoring the wet signal path, since the setting on that trim pot can affect whether you hear any changes at all.

 

[Matoni]

jut got my new chips from cabintech, the place Robert recomended. It doesnt fix the problem. now I do hear though a chip every time the LFO light blinks. Bummer the new chips dont work. I was really hoping they would fix the problem.

 

[Matoni]

OK I GOT IT!! Im so excited. using McKnib's methodology, I probed pin 7 to make sure it was connected to the diode... and it wasn't. I figured out that the trace between the 47pF capacitor and that diode got cut, probably when I took out my 47nF capacitor. Thanks for all your help guys. I really appreciate all the time and effort that went into helping me figure out what was wrong with this pedal. Next up is going to be the XC phase board, which hopefully I wont have any problems with. Ill let you great people know if I have any issues with that. Thank you again for all of your help and support.

 

[giovanni]

Awesome! Mark it solved!