Oscillator success! And yet more troubleshooting

KOSMO MODULES
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I have one simple CEM 3340 VCO with PWM 100% operational! What a relief. I am troubleshooting my second one now and it is almost all working - all of the wave shapes including the PWM function but for some reason the course tune has nearly no effect, the trim pot does nothing, and the CV does nothing either.

Any quick fixes before I go back to staring at it?

Also, I think my ADSR is working - the lights light up - but it seems to have 0 impact on any audio signal that I run through it. Is there a good way to test it out if I dont have a VCA? I do have my VCLFO working too, if that helps any.

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You don’t run an audio signal through an envelope generator. You give it a gate signal, it outputs a control voltage which commonly is used to control a VCA. But you could also put it into the CV input on an oscillator and it’ll change the oscillator pitch, up and then back down.

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If you’ve got 2 and one is functioning then the obvious thing to do is compare the circuits. You can do that by eye or do some measurements. What sometimes helps in finding the problem is doing side by side measurements. Measure something in the circuit that is working and in the exact same situation measure the same in the other. If you have an oscilloscope, then I’d advice using that. If you don’t then you could measure (all devices switched off) resistor values using a multi meter in the circuits and see where they deviate from another (once more: power is off). When doing so keep in mind that you are not measuring the resistance of the component alone you connect the multi meter to but also the other components it is connected to. Whenever you find a significant deviation, ask yourself whether there is a logical explanation for this and if not investigate further. Note that it is wise to put all potentiometers of the devices you are comparing in about the same position.

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There’s about 2 million posts in this forum telling you how to measure the inputs to the CV summing node (pin 15) :grinning: . Here’s one:

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Thanks for the tips. Doing some comparisons between the two units was what helped me fix the first one. I just need to go a bit deeper and have a better test setup on my desk. Right now its difficult to get power to them to do diagnostic work.

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