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.

 

[Mcknib]

C11 should be 47pf yours looks like 473 or 47nf

That'll obviously affect your clock output

 

[Matoni]

So I just reflowed all the solder for the entire board. It still doesn't work, but in the noise coming from the board I can hear a slight pulsating sound going at the same speed as the LFO LED. I like to reflow solder with the effect on to help with debugging, and something extremely strange happened when I put my soldering iron on pin 1 of Q2. I started to hear a pitch that had a modulated depth that changed as I changed the depth pot. still no chorus signal though for my guitar even with this. I will now go trace the LFO signal from the depth knob all the way to the 3102 chip. Let me know if what I found means anything, or if it is just a coincidence.

 

[Matoni]

C11 should be 47pf yours looks like 473 or 47nf

That'll obviously affect your clock output

I didnt see this message until right now!! I don't have any 47pf caps, will a 51 pf cap work or should I order a 47 pf. And you were right, this was the wrong value. Im so glad you spotted that. Thank you so much!!

 

[Matoni]

Just tried switching out the cap for a 47pF Silver mica cap I had lying around from another build and I am still getting no chorusing, but the clock is reading 1k hz now so thats at least a little bit better. Thanks for pointing that out to me.

 

[Matoni]

and I just traced from the depth knob to the clock chip and everything looks good. I will order the new chips as soon as I can to see if it is a chip problem. Thanks again for all your help.

 

[Mcknib]

I'd post all your IC pin and transistor voltages that might lead you to your problem area

 

[Matoni]

so what exactly should I measure? The voltage between each pin of each chip and transistor and ground? or did you just mean the chip power voltage? I'm not completely sure what is needed here.
if you meant what I said at first, here is the voltage between each pin of each chip and ground:
IC1: pin 1: 1.6vdc, pin 2: 4.3vdc, pin 3: 4.3vdc, pin 5: 4.3vdc, pin 6: 4.3vdc pin 7: 4.3vdc, pin 8:8.6vdc.
IC 2: all pins besides pin 8 (and obviously pin 4 because it is ground) are 2.7vdc, pin 8 is 8.9vdc
IC3: pin 1 and 2: 0vdc, pin 3: 2.1vdc, pin 4,5,6: 8.6vdc, pins 7,8: 3.7vdc
IC4: pins 8,5,1,2: 8.6vdc, all other pins 0vdc. This is still measuring at 0hz for some reason off pins 2 and 4. Maybe it is just a bad chip? new chips are on the way.
Q1: pin 1: 2vdc, pin 2: 2.5vdc, pin 3: 8.6vdc
Q2: pin 1: 3.4vdc, pin 2L 3.9vdc, pin 3: 8.6vdc
Q3: pin 1: 2.1vdc, pin 2: 2.9vdc, pin 3: 8.9vdc
Q4: pin 1: 0vdc, pin 2: 0.6vdc, pin 3: 20mVDC (this seems like a problem, no clue what is causing it. The cap I put in is for amps so it is way over specked, I don't think that should be a problem though.)
Q5: pin 1: 2.1vdc, pin 2: 2.5vdc, pin 3L 8.6vdc

everything but Q4 looks about right I think? let me know what you guys think may be wrong given this new information. Thank you again for all of your help.

 

[Mcknib]

Voltages don't look right to me you'd want around 4.5 (half power) on all the VREF points

Pin 3 of the BBD is the bias pin that should have around VREF voltage too I think, you'd defo need more than 2.1v

VREF is set by the trimmer and VREF B by the voltage divider R100 and 101 that looks ok with your IC1 voltages and LFO sounding like it's working

What voltage do you get on the trimmer middle lug try adjusting that to 4.5v ish

 

[Matoni]

I just adjusted the bias pot to 4.5 volts, still doesn't work. Would you like me to send out the new list of voltages for the BBD? I'll do anything I need to do. Thanks again for all your help.

 

[Mcknib]

What's the voltage on pin 3 of the 3207 and IC2 pins 3 and 5

 

[Matoni]

IC2 pins 3 and 5 are measuring at 4.5 volts DC and IC3 pin 3 is measuring at 3.8vdc. Hopefully, this helps. I have no idea why this pedal is being so difficult. Hopefully, with your guys' help, I am able to resolve this quickly!

 

[Mcknib]

Check your Q3 voltages the emitter should be round about the same as pin 3

Try reflowing Q3, the joints look ball like and may be partially dry inside and causing some resistance to voltage

Obviously only reflow for around 4 seconds per pin till you see a nice solder flow you don't want too much heat frying your transistor

It's just a process of elimination you've now got your VREF set correctly, so all the VREF points you can see on the schematic should have the same voltage as the trimmer middle lug if they're not you'd just trace it back using the schematic to see where it stops or changes

Pin 3 voltage is almost there so again you'd trace back to Q3

 

[Matoni]

The voltage on the middle lug of Q3 is not 4.5 volts. Is this a problem? I reflowed the solder. I will send a picture of the bottom of the board shortly and you guys can tell me if theres anything that looks sketchy going on under there.

 

[Matoni]

wait never mind I was measuring the wrong transistor. The middle pin of Q3 is 4.5 volts. THis is what I would expect it to be. PLease let me know what the next step is.

 

[Matoni]

As promised, here is a picture of the bottom of my board. Hope this helps us in figuring out what is wrong with this thing.

 

[Mcknib]

You've a few dull looking joints on the BBD and clock

Remove the ICs from their sockets and reflow the socket joints

Clean the pcb with isopropyl alchohol or something similar

All the steps taken so far are basically trying to confirm whether your clock and or BBD are faulty ie make sure the surrounding circuitry is doing what it's supposed to there's nothing worse than replacing an IC and it's the same, so you're best trying to diagnose it properly although it's time consuming it's also a learning opportunity

From your description you do get clean signal and the LFO works with varying voltage on the IC output pins so gotta be something on the wet side again you've improved things with a higher bias voltage on pin 3 albeit I don't know if 3.8v is high enough or it needs to be 4.5v minimum

If someone has working voltages they can post that'd be good

You've fixed a few things so can't be that far away

 

[Matoni]

Ill order a new clock and BBD, as well as reflow the solder on these ic sockets. I doubt that this will fix the problem, but its not a bad idea to try and make sure that everything else is OK.

 

[Bio77]

CE-2 is a weird circuit the bias sets the VREF.

Ill order a new clock and BBD, as well as reflow the solder on these ic sockets. I doubt that this will fix the problem, but its not a bad idea to try and make sure that everything else is OK.

When you reflow the IC sockets, it'd be a good idea to add some solder. Just a touch on each joint.

 

[Matoni]

As expected, it didn't fix anything. Let me know what I should try next.

 

[fig]

Out on a limb here…check that pin one of IC2 is not folded under. It appears that a partially dry signal might still make it to output.

Then again, I have no idea if that makes any sense.