Choral Reef Troubleshooting

[jdw8z]

I'm getting the dry signal on the Choral Reef but no wet; when I turn the mix knob all the way up there's no sound. I measured all the voltages and they're maybe a little low (battery was reading a bit below 9v too) but they're consistent with what they should be. I tried making an audio probe and I traced to R16 (12k). On the diode side of it I get signal but not on the side that's connected to Pin 1 on the MN3008, R17, C6, and Pin 14 on the CD4047. I tried replacing R16 but that didn't do anything, and I used a multimeter to check connectivity between R16 and those other parts and that's fine. Any ideas what to try next? I can upload pictures if need be, but the board is so packed that it's honestly hard for me to see much in person, not sure how much pictures will help.

[gordo]

Can't hurt.  Good place to start.

[Aentons]

Where did you get you mn3008 from? Could it be a fake?

[jdw8z]

Here's a link to some images: https://imgur.com/a/jcQbDiY

Note, the extra pink wire coming from the 9mm pot is there because I messed up the rivet in the PCB so I ran the extra wire to a trace point where that pot is supposed to be connected to. I tested the connectivity with the multimeter, so that's not the problem.

And as for the MN30008, I got it from Smallbear so I hope it's not fake or defective. Would that cause no signal to come through the audio probe at the point I mentioned earlier? Like I said, the voltages are reading more or less correct on it.

[shedland]

I've had a similar situation with a Porkbarrel Chorus.

I used an audio probe/circuit tester that's i built following instructions I found on the tagboard effects site.

http://tagboardeffects.blogspot.com/2014/09/test-box-20.html?m=1

Once you have built this you will attach your pedal PCB to it and hook it up to your amp or other similar item.

You'll need the schematic for the Choral reef, and the circuit tester, from there you will check where the audio ends, For example test to see if audio is making it to your BBD, or other major devices, it's a fairly easy way to trouble shoot, and in this case avoids you swapping out expensive/obsolete components in an attempt to guess where the fault is.

Sorry missed the part where you had said you were using an audio probe.

[Scruffie]

There's a good reason pin 1 of the MN3008 doesn't give you any sound... it's the supply voltage.

Try looking at pin 13 followed by 6 instead.

[jdw8z]

Sorry, I got confused because it looks like the MN3008 is numbered backwards on the schematic for some reason (i.e. what's labeled "2" on the schematic is actually position 13, though the lines are correct regardless). In that case, when I audio probe 13 (the chip input) I get signal, and when I probe the outputs (6 and 7) I get flickering static. When I probe 9 and 2 (the controls?) I get louder flickering, which I'm guessing is the rest of the circuit doing the modulation?

I can also note that at one point when I went to re-test it worked for a brief while, but then back to the same problem. And the connectivity and voltages seem to be fine. Here are the MN3008 voltages I'm getting:

1. 8.33
2. Varying? Between 3.9 and 4.5
6. 6.49
7. 6.49
8. 0
9. Varying, between 3.9 and 4.4
13. 7.65
14. 0

Am I likely looking at a bad chip, or if something were shorting further back in the circuit - say the CD4047 or the SPDT switch, for example - could that be causing the problem? Is there some way I can test the circuit without the MN3008 to see if everything else is fine?

[Scruffie]

Pins 2 & 6 are the clock and shouldn't be varying, seems it's probably around the 4047... no good clock, no delay signal.

[jdw8z]

Solved the problem. I must have just completely screwed up the traces on the width pot when I had to resolder it. Anyway, the left lug of that pot wasn't connecting to R12, so I just added a wire to make the connection and now everything works!

[tcpoint]

Good job.  I really like the Choral Reef.  Played with a lot, this last weekend.  My daughter's boyfriend really liked it a lot, as well.