Ive recently got out my theremin I built last year and never had the time to finish with moving house etc. Ive managed to finish most of it off now and when grounding to tune the pitch that all works fine. But without the grounding on U3 I get no sound out. For a short time If I literally rubbed L8 I got sound so its the volume section thats faulty.
Ive checked all the voltages on U3 and everythings right or at least within what it should be.I read that u3-13 should be 2v when U3 isnt in and R14 is grounded and it is but as soon as U3 goes in and the ground comes off it goes to 0.02v.
I also checked over a few voltages and found that r16 that is marked on the schematic as 0.2v was only 0.01v. So I tested r16 in situe then took it out to make sure and sure enough it was 2.2k I tested the -12v at that point too and it was fine. So I put r16 back in and tested it again now Im getting +12v on it which also seems to put +12v on the emitters of both Q6 and Q7. Needless to say first thing I did was check for anything that was shorting on the board through desolering and resoldering but everything checked out.
Also I seem to be getting 0v on D1 anode and +3v on the cathode.
Ive checked all the connections and they all appear to be correct as do the values of the parts. Not sure where to check.
Not sure where to go from here. Everything else seems fine and Im guessing the +12 on Q6E and Q7E are whats causing the D1 reading to be wrong. I guess that does feed to U3-13 too so could be the cause but where its comming from I dont know.
Any thoughts or suggestions?