Jaycar/Silicon Chip Theremin MKIII volume plate not working

Posted: 11/19/2021 9:48:52 PM

Joined: 11/19/2021

Hi everyone. 

I bought a kit from Jaycar of the Theremin MKIII to build for my sister-in-law for her birthday.  I have a rough understanding of electronics, and have become quite good at soldering from some previous projects (plus my father is an electronics technician, so I've picked up some tips).

Unfortunately after building the kit, the volume plate does not seem to be working at all.  Moving my hand closer or further away from the plate does not change the volume at all, no matter how the volume thumbwheel is set.  Sometimes there is a slight pitch change when my hand is closest to the plate (which could be because my hand gets close to the antenna), or the sound cuts out completely when my hand touches the plate. 

The circuit has 12 or so test points to test the voltage.  The instructions include what these voltages should be, and I did see some variance with my readings, but I'm not sure if they are within a certain tolerance.  I can provide a list of the test points, what they should read, and what I saw in my testing, if needed. 

I've checked that all of the components are soldered correctly, in the correct orientation, etc and everything seems fine.  The board and instructions make it very clear which component goes where, and in which orientation when they are polarised. 

If anyone can suggest anything to check, it would be greatly appreciated

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