Electroharmonix polyphase where to set bias

[frank57]

I have an old Polyphase pedal and I've retouched everything in there.
The photo shows the way it was with bent over leads etc.
I'm not that great at reading schematics, and I'm not sure where exactly to set the bias of 6.7 volts.
I measured across the cap next to the trim pot,and it's 6.7 volts
but someone told me I should measure across the trimpot leads. There I get 2.2 volts
Is he right?
I found one schematic but I'm not sure it's the right one.
Any help would be appreciated!

 

[ModemHead]

The 15K, 8.2K and the 10K trimmer form a voltage divider to create a "virtual ground" rail somewhere about midway between 0V and +15V. It makes a zero reference point for the AC audio signals to swing positive and negative in the LM324 opamp circuitry. The 68K and thermistor is apparently there to alter this voltage based on temperature. The 220uf capacitor is there to keep the reference voltage steady. So I'd say the 6.7V should be across the capacitor.

 

[frank57]

If that's the case I'm ok because that's what i did I measured across the 220cap.
Only thing I got elsewhere was "The wiper of the trimpot in the env LFO section is where you measure."
Not sure what to check with that info though? Across the pot?
Everything works right now.
The envelope section before wasn't working very well and there were some connections between the two pots that had no continuity.(env mod and mod rate)
So that was fixed and things started to work a lot better. Some lifted pads too.
The rate knob in sweep mode tends to fart out set all the way, so maybe the pot is overturning?

 

[ModemHead]

The wiper of the trimpot appears to be grounded (schematic's a little fuzzy, but that's how I interpreted it), so there doesn't appear to be much measuring to do there. In any case, if the schematic is correct, the maximum voltage across the trimpot could only be about 15*10/(10+8.2+15) = 4.5V.

 

[frank57]

I'll see if I can find a better schematic that's a bit clearer.
But it looks like measuring the cap is probably right.
I'll scan in one I printed out.

The problem I have now is the rate control when in sweep mode seems to be making a background noise when I set it about 7 out of ten.
So you get the warbly tremolo leslie effect but there's a noise behind it like a knocking type noise.
The same rate almost like a clock.
Did I misconnect something? Any ideas?
The envelope section seems too be working for the first time since I had the pedall really.

 

[ModemHead]

So you get the warbly tremolo leslie effect but there's a noise behind it like a knocking type noise.
The same rate almost like a clock.
Did I misconnect something? Any ideas?

I won't even pretend to know how any of that circuit works. But for a wild guess, maybe the transitioning back and forth of the Q output on the 4013B is coupling a little tick into the audio somewhere. If the unit is old, maybe swap out those two electrolytic caps (10uf?) between the 4013B and the 3140 opamp. Also try bypassing the +15V and Gnd rails with a 0.1uf cap in the vicinity of those ICs.

 

[frank57]

Well, I got rid of the noise!
It seemed to be related to the wiring either on the pot or from the switch to the ground track.
So it's all working and sounding great!
The envelope section never sounded this good.
Only thing that happens now is the rate switch in sweep mode,when it gets to about 8 and you get that warbly effect
( a lot of oscillation)
it tends to do nothing after that(from 8-10) and the signal is normal(no phase effect).
Perhaps that's normal ? How much more of a warble can you get?
Maybe the pot is kaput or still something happening with the wiring.
It's like the rate pot keeps on turning but does nothing after 8 or so.