Cepheid Chorus No Effect

[Jonathan1986]

I just finished a Cepheid chorus using MN3007 and MN3101 Clock. With the Effect engaged I get no effect. The Dry signal comes through as long as I have the trimpot dialed in but no effect, regardless of the settings on both the main external pots. Any suggestions on what the culprit might be?

 

[BuddytheReow]

Posting some pics of your build will get better traction here. Have you followed the build doc correctly? This one contains a special jumper depending on the BBD.

 

[Stickman393]

Photos would help. Unfortunately the dry side is far easier to diagnose than the wet side. There majority of the circuit is dedicated to the wet side.

Does your rate LED pulse? If not, you might have a problem with your LFO.

Your starting point on that trimpot should be 50%. I'd keep it there until you have some kind of chorusing effect.

 

[andrewsrea]

I am working through the exact same thing right now!

My build modified the 'Cepheid' to a 'Cesar'. I finished it a week ago and it was distorted with the Blend on '0' (no effect) and then it quickly went silent as I blended in the effect. My LFO LED was blinking and reacting appropriately to the rate control.

I was using 18vDC power supply (which loaded and trimmed by D100 - 1N5817 diode, the Vcc = 17.5) and used a 15v Zener for D101, which in practice only regulated the Vcc B down to 16v and Vref B to 8V. Accordingly, I swapped D101 for a 13v Zener and am getting 14v, which is where MN3007 and MN3101 are supposed to operate well (they can take 18v max before damage).

I socketed all my ICs and transistors and am expecting to get to loading just IC 2 and the transistors, to see if the dry side is working right. If successful, I will load IC 3 & IC 4 to see if signal will pass (it should without the LFO, IC 1, wiggling it).

I am hoping it works as these chips are NOS that I purchased in the 80's, left over from a Roland JC120 restore. I am wonder if @Robert knows if this BBD + Clock chipset was ever verified with this PCB? In comparison to the original Boss CE2, it should. The only difference I found is that for the MN3007 CE2, Pin 1 is ground and Pin 5 is -15v, where the Cepheid has Pin 1 at +15 and Pin 5 to ground, which is electrically the same thing.

Let me know if you figure it out and I will keep you posted on my progress.

 

[Stickman393]

I can attest to the MN3007 and M3101 working in the Cepheid. That's what I built mine as.

 

[Jonathan1986]

by popular demand, pics! Some FYI’s, Q4 & 5 are 2SC945P like the original and are E-C-B pinout, hence why they’re twisted. And C4 is the correct 220uf value, just large. For the zener diode I used a 12v.

 

[Jonathan1986]

Photos would help. Unfortunately the dry side is far easier to diagnose than the wet side. There majority of the circuit is dedicated to the wet side.

Does your rate LED pulse? If not, you might have a problem with your LFO.

Your starting point on that trimpot should be 50%. I'd keep it there until you have some kind of chorusing effect.

The LED pulse works and changes speed with the Rate knob. When the effect is engaged I get the dry signal only with the trimpot adjust roughly half way, otherwise I get no signal.

 

[Jonathan1986]

Posting some pics of your build will get better traction here. Have you followed the build doc correctly? This one contains a special jumper depending on the BBD.

As far as I know I did everything correctly, not 100% sure though

 

[Stickman393]

Looks like R25 is a 2k, should be 2.7k. Not sure how much of a difference that would make though.

What you've described narrows it down a bit, your issue is somewhere in the circled area:



Check your BBD and clock legs, sometimes they'll bend in on themselves when you put em in the sockets.

Also, take a look at your solder joints for the components circled. Re-flow if necessary, keep an eye out for solder bridges.

 

[Stickman393]

Also, how old is this board?

Something I didn't mention before (it's been ages since I did mine and I just remembered): the Cepheid I built was an early version. The board contained a single mistake, illustrated by this screencap:



IIRC, this got fixed shortly after release. If you've got an older board, that might be the issue.

Test for continuity between each side of R27 and IC3, pins 1 and 7/8.

Basically, one end of R27 should show continuity to pins 7/8, and the other should show continuity to pin 1. On mine, I was missing the connection between R27 and pin 1, because that side of the resistor was on the wrong side of the mn3207 jumper pad.

IF this is the case with yours, it's an easy fix. IIRC, the pad closest to IC3 is connected to pins 7/8. I soldered one end of r-27 to that pad and directly soldered the other end of the resistor to IC3 PIN1.