WSG: lost my zaniness

[stevebryson]

Hi Folks - I hope I can get some help with a problem I have with the wonderful weird sound generator.

I rewired my weird sound generator with shielded wire to eliminate crosstalk (very successfully, I might add). I actually had to do this twice because the first wire I chose was too stiff to fit in my case. But outside the case after the first rewire the WSG worked perfectly! I re-rewired with thinner shielded wire. Crosstalk is still completely gone, but the zaniness knob has no effect on both oscillators.

I verified via oscilloscope that the zany oscillators are putting out the expected square waves with varying frequency. What could I have broken that would break both zany functions? The zaniness B pot is behaving strangely, and it's possible that I got solder inside it, but the zaniness A pot is behaving as expected (expected resistance at various pot positions). But there is no response at all in the A and B weird frequencies to moving the A and B zaniness pots.

I checked the wiring several times, and the zany square wave is going into the zaniness pot (ZA1A and ZA1B) as expected. No signal is coming out of these pots (ZA2A and ZA2B) regardless of the pot position. I don't know what I should expect at ZA2A and ZA2B. I ran ground rails from the ground connections in both zaniness pots to ground the shielded wire, but this was true in the first rewire and the zaniness worked fine. Ground continuity is as expected, and no wires or pots are incorrectly shorting to ground.

The weird and wacky oscillators are working perfectly (no crosstalk!) as is the wacky function.

Any ideas for what to look at? Could a problem in zaniness pot B take out zaniness A? They share the ground connection... I replaced the U1 chip just in case with no change.

I really enjoyed writing a post about lost zaniness

[elmegil]

Only thing I can think is, are your 3904's working correctly? They're what actually makes the weird get zany.

[stevebryson]

Thanks, elmegil. I wondered the same thing, but I don't know how to test them on the board. Anyway how could I blow both of them?

I discovered, though, that if I short ZA1A and ZA1B I get zaniness on weird osc A, and shorting ZA2A and ZA2B gets zaniness on weird osc B. So that means I managed to kill both zaniness pots, right? I guess I'll be buying new pots.

[elmegil]

I assume you mean short the output of the zany oscillator to the wiper of the pot? (the schematics I'm looking at label them differently).

If so I'd agree, somehow the pots are messed up.....

[stevebryson]

Yes! Replacing the zaniness B pot restored both A and B zaniness. So failure of that one pot affected both. Now everything's working!

Elmegil: Thanks for your help. I find the reconciling panel wiring and the schematics a little difficult: in the panel wiring diagram it's clear what I mean by "short ZA1A and ZA1B", but it's hard to see how shorting them will have the same effect in the schematic.

[elmegil]

I am baffled that B could affect A.

However, you're right I see on the wiring diagram how that might be a logical thing to try.