moog moogerfooger mf-102 pedal bypass problem

[beatnik]

I have this very nice ring modulator pedal by moog and the bypass function stopped working

The pedal is always ON, footswitch don't make a difference, and the "BYPASS" and "LEVEL" LEDs don't light up

Unfortunately there are no schematic available, although I have found a traced schematic for another moogerfooger pedal and checked against mine the bypass section is the same.

I have checked the power supply voltages and there seem to be a problem with the negative rail. On the input of the voltage converter i have +8.22V and on the output i get -6.79V

A bit low, but seems to me this voltage doesn't affect the logic circuit

Don't know a lot about logic bypass circuit so i'm stuck with this and I would really like to fix by myself instead of having to ship to moog and spend a lot of money.

Any help is highly appreciated

Schematic of model mf-101

https://www.dropbox.com/s/a9j080l6h2...F-101.png?dl=0

[MarkusBass]

The circuit is very simple. The switch (normally open) provides 0V to the input (pin #1) of U13 (binary counter) when pressed. And the output of the counter (pin #12) changes the voltage from 0 to 9V and back to 0.
So the first step is to check if you have initially 9V on pin #1 of U13, and does it change to 0V when you press the switch, and does this change the voltage on the output (pin #12) of U13.
However, the fact that the LEVEL LED also doesn't light up may suggest that you have general problems with the power supply (for example with +9V rail). What kind of power supply do you use with the effect? It should be most probably +9VDC. If you have less than 9V, or you use AC power supply, this could cause the problems.

Mark

[beatnik]

hi Mark, thanks for your reply.

I am using one of the regulated 9V outputs on my BBE Supa Charger, with the proper polarity reverse cable.

the power supply section seems fine, although the voltage converter from +9V to -9V outputs -6.8V instead. But i think that voltage doesn't go to the bypass circuit

I have checked CD4024 operation as you recommended. on pin 1 i have 1.9V that goes to 0 by pressing the switch. on pin 12 i have 0.7V and that doesn't change with switch operation

on pins 12 and 14 of 4049 (U4 on the schematic) i got 0.1V so that's not giving enough power to the status led

i wonder if the problem is on the CD4024 or further down the line

[MarkusBass]

the power supply section seems fine, although the voltage converter from +9V to -9V outputs -6.8V instead.

U15 is a charge pump. It converts +9V to -9V. It happens that the inverted voltage is different from the input value. Especially, when the current drawn from the output in higher. Please check that on the input of U15 (pin #8) you have +9V and on the output (pin #5) you have -8V.

I have checked CD4024 operation as you recommended. on pin 1 i have 1.9V that goes to 0 by pressing the switch. on pin 12 i have 0.7V and that doesn't change with switch operation.

Clearly CD4024 is not working correctly. On the input there should be 8 - 9V. This can be caused by low impedance of the meter you use. What meter do you use? The resistor on the input has high value - 3.3M. You need a meter with at least 10M input resistance to measure that voltage correctly. Please check whether you have +9V on the other lug of the resistor. Also make sure that CD4024 is supplied with correct voltage (pin #14 +9V).

Mark

[beatnik]

supply voltage is 9.1V / after the polarity protection diode 8.3V / after charge pump -6.9V

on one side of 3.3M resistor i have 8.3V and on the other going to CD4024 pin 1 i got 1.9V. pin14 gets 8.3V

i am using a cheap EM129 multimeter. the manual states input impedance is 10M for all ranges but i don't really know how true that is

[beatnik]

i've tried with another multimeter (cheap one as well) and the voltage on 3M3 resistor is 6.19V but pin 12 is steady on 0.7V again

[MarkusBass]

So the power supply is OK, the resistor is OK, the second multimeter is OK. It seems that the counter has failed. You can do two things:
- either solder 10k resistor parallel to 3M3 (temporarily) and see if this changes anything,
- or buy CD4024 and 3M3 resistor and assemble the circuit on a breadboard - just to see how it works. If it works correctly, replace the IC in the effect.

EDIT: what is important for the switch is the change from high level to low level. So make sure that when the switch is pressed, you get 0V on the input of CD4024.

Mark