MicroSynth; any ideas??

[Bernardduur]

Hey all!

I just got a MicroSynth from a friend and he always disliked the effect as he "thought" it was working properly. Now that he put it next to mine he KNOWS his is broken......... Shame is to say he didn't used it for a long long time as he "disliked it" and thought it should sound like that

What happens:
When it powers up no problems. Now when I hit a note the voicings work properly (sub, guitar, octave, square) and the attack decay is just OK. Only it won't sweep.......I tried multiple trigger settings and none just work. The start freq knob does what the stop freq knob does on my unit: it sweeps the freq.

Somebody have some ideas on what can be wrong with this one??

[George Giblet]

Do you know if the squelch control is working?  With square-wave only you should be able to hear the noise cutting out:

no: look at envelope filters, and check DC offset from rectifier is changed by the squelch control.  If no change in DC look at the envelope circuit.
yes: As a first step I would take a 100k resistor and connect it to +V and then to the junction of C11 and the trigger pot.  Adjust the trigger pot and look at the DC at it's output you should see small changes in DC voltage.  You should also see that the STOP pot no longer functions and that the START pot can now control the sweep (I think).   If not, check the comparitor outputs, both part of IC7/A7, are changing as you vary the trigger pot position.

[StephenGiles]

Check the wire connections to the stop & start frequency sliders.

[Bernardduur]

Thanks all!

I tested the Squelch trimpot and it works.....

Weird thing happened; I came home with it, plugged it in and it WORKED....... then I turned the squelch trim and it was back to the way it was as my friend described. No loose wires or such. Is the Squech setting so "tight??"

I will test your thoughts in the weekend!