[sdiy] SOMA Lyra-8 vibrato stopped working

frey at radioles.com frey at radioles.com
Sat Mar 9 04:57:41 CET 2019


Adam and list, I have a multimeter and an oscilloscope. I tested continuity around the vibrato switch and it was ok. There is a trace off of a header that runs to 2 cd4093be ICs. I checked that when the vibrato is in the on position voltage at the vdd pin goes to 16v.
 And, just now one of the two cd4093be chips released the magic smoke. Dang. This synth is bisymmetric meaning it has 2 groups of 4 oscillators, hence two ICs l suppose.
 Can anyone point me in the direction of vibrato circuit schematics so I can try and figure out how this one works and where the components are I need to check?
 Thanks. JoeF.

On Mar 7, 2019, 6:34 PM -0500, Adam Inglis <21pointy at tpg.com.au>, wrote:
> What test gear do you have Joe?
> If you’ve been fiddling and something has stopped working, might be good just to do some continuity tests around the connectors and those boards.
>
> However, the pitch of the VCO must be seeing some voltage from the vibrato circuit - maybe the LFO has failed? Does the LFO work as it should on any other part of the synth, say, the filter?
>
> A
> > On 8 Mar 2019, at 8:10 AM, frey at radioles.com wrote:
> >
> > Hello, I modified my Lyra-8 by adding switches to the touch contacts so I could have a single oscillator work when switched on. I did this without modifying the pcbs only wiring the switches in parallel with the contacts bolted to pads on the pcb.
> > However, somehow in removing the pcbs to install the switches I have caused the vibrato switch to stop working. When I flip the vibrato switch on, the Lyra audio output frequency shifts upward but never back down and does not oscillate as a vibrato should.
> > I have found on one of the pcbs a connector header that runs from board to board marked vib and if I trace it back I come to an IC CD4039. I mention this to see if it is a clue for some of you with experience troubleshooting what I should look for that may be malfunctioning. Should I see an oscillating voltage here or what?
> > Any advice would be most helpful. JoeF.
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