SOLVED Cepheid Chorus No Chorus…

[Coda]

Just finished a Ce-2. I used a MN3207/MN3102 pair. I get no effect when the pedal is engaged, just clean tone. I know it’s a crap shoot with BBD’s from EBay, but I bought from a seller others have had success with. My issues is I’m not sure where to start. The rate LED works, and changes with the rate control. Does this mea the clock chip is good? Or does this mean the BBD is good. I imagine that a pulsing LED means the clock chip is fine. Am I correct?…

 

[Robert]

The pulsing LED means the LFO is running but it doesn't tell you anything about the BBD clock.

You can measure the frequency on the clock pins.

Have you adjusted the trim pot? If not, start a full CCW and slowly turn up the trim pot. You should hit a narrow spot where you hear chorusing, then tweak until you find the cleanest setting.

 

[Betty Wont]

If you are getting clean tone and no effect and the rate indicator is working, then likely its a bad 3207 or clock. I assume you are getting nothing while adjusting the bias. I believe that one doesn't want to get above 9v either, so a voltage check is in order.

 

[Coda]

The pulsing LED means the LFO is running but it doesn't tell you anything about the BBD clock.

You can measure the frequency on the clock pins.

Have you adjusted the trim pot? If not, start a full CCW and slowly turn up the trim pot. You should hit a narrow spot where you hear chorusing, then tweak until you find the cleanest setting.

I messed with the trimpot, but I would t consider it an “adjustment.” I’ll try your suggestion and report back…

If you are getting clean tone and no effect and the rate indicator is working, then likely its a bad 3207 or clock. I assume you are getting nothing while adjusting the bias. I believe that one doesn't want to get above 9v either, so a voltage check is in order.

Voltage on both chips?…

 

[benny_profane]

Voltage on both chips?…

Yep. Note that you should get variable readings from pins 5, 6, and 7 on the clock chip.

 

[Betty Wont]

Voltage on both chips?…

The supply voltage after your (presumed) zener diode. Make sure you aren't getting more than 9v to the 3207 or it will fry.

 

[Scruffie]

The supply voltage after your (presumed) zener diode. Make sure you aren't getting more than 9v to the 3207 or it will fry.

Nah, it's good to IIRC... 11V is terminal, perhaps even 12, but 9-10V is fine.

 

[Betty Wont]

Nah, it's good to IIRC... 11V is terminal, perhaps even 12, but 9-10V is fine.

Good to know. I always thought those were right on the edge.

 

[Deperduci]

Not really but good diodes prevent melt downs.. had this MXR 117 flanger clone I couldn't finger out why it had no response when all solder joints and jack wiring were right, good and correct components until I saw my power wire was attached inverted.. diodes saved about $50 worth of chips... "9v' rating and the headroom on the chips are all part of 'tolerances'

 

[Coda]

I adjusted the trimpot. I started full CCW; no sound. I slowly started turning to the right, waiting to hear chorusing. Eventually it went a bit distorted, and then no sound fully clockwise. I also just noticed that the 3102 is rather warm to the touch…Below are the voltages:

MN3207
1- 0
2- 2.96
3- 7.14
4- 5.27
5- 6.04
6- 5.13
7- 2.3
8- 2.2

MN3102
1- 6.03
2- 5.12
3- 0
4- 2.96
5- 4.68
6- 4.86
7- 0.56
8- 5.26

RC4558
1- 7.91
2- 7.92
3- 7.92
4- 0
5- 7.91
6- 7.91
7- 7.91
8- 8.69

TL022
1- varies
2- varies
3- varies
4- 0
5- varies
6- varies
7- varies
8- 6.03

 

[Scruffie]

I mean, even without the warmth, that 3102 ain't working.

When you pull it out, hopefully you'll get 9V back on the 3207 pin 5.

 

[Coda]

I mean, even without the warmth, that 3102 ain't working.

When you pull it out, hopefully you'll get 9V back on the 3207 pin 5.

I’ll swap in some more. Are there any “hallmarks” I should be looking for?…

 

[Coda]

Small update: I swapped in a few different combos, and I was able to dial in some chorus with the trimpot. It’s super distorted, but it’s chorus. I think that’s a step in the right direction…

Edit: it seems now that the distorted chorusy effect comes and goes. I have to keep dialing it in.

 

[benny_profane]

It seems like your LFO is working, so this might not matter, but is that 33R resistor dropping nearly 3V?

 

[swelchy]

Shoot me over your address and I’ll mail you some legit chips for it… I bought extras when I did my Caesar last week sourced from cabintech

 

[Scruffie]

Small update: I swapped in a few different combos, and I was able to dial in some chorus with the trimpot. It’s super distorted, but it’s chorus. I think that’s a step in the right direction…

Edit: it seems now that the distorted chorusy effect comes and goes. I have to keep dialing it in.

When you swapped in the new 3102, what voltages did you end up with on the 3207?

Your new problem, assuming it's not the V.Ref drifting, sounds like it might just be related to a bad solder joint or wrong resistor value around the BBD itself.

 

[Coda]

When you swapped in the new 3102, what voltages did you end up with on the 3207?

Your new problem, assuming it's not the V.Ref drifting, sounds like it might just be related to a bad solder joint or wrong resistor value around the BBD itself.

Here are the updated voltages:
MN3207
1- 0
2- 4.29
3- 3.94
4- 8.2
5- 8.7
6- Varies
7- Varies
8- Varies

MN 3102
1- 8.76
2- Varies
3- 0
4- Varies
5- Varies
6- 8.3
7- Varies
8- 8.2

I am starting the "great double check" right now...

 

[Coda]

All of the resistors are correct. I guess its on to the caps now...

 

[Coda]

All of the caps are correct. On to the cleanliness inspection...

 

[Scruffie]

The voltage on pin 2 & 4 of the 3102 (and by association pin 2 & 6 of the 3207) should be a steady half supply, possibly you might have burnt out the 33R resistor causing its voltage to fluctuate with frequency...