I recently was able to buy an SLM Concert Spectrum which is my absolute dream synth. There are a few problems with it that are not so obvious to me, as I haven’t really worked on a string machine before. Many of the sounds are a bit quiet or downright inaudible, though I know the fix for that is probably just re-capping the audio line stuff.
My main issue is that the fast LFO for the BBD chips is not running. The slow one runs fine (and trims fine too,) but the fast one does not, even after replacing a capacitor that seemed faulty.
The other biggest issue is in regards to keying on the piano and harpsichord tones, which do not work on some keys and are intermittent on others, though I imagine those will also need new capacitors of some description.
One final weird issue is the Horn/Trumpet doesn’t work over the split point, so something is probably wrong with the audio line with that, but that’s not my biggest concern as of yet.
I have talked to a friend who has general experience with synth repair but string machine specific stuff is not his wheelhouse, so I am hoping someone here will have an idea of good steps to take to fix that LFO as a starter and maybe some advice on the keying.
I also bought a pdf of the original service manual for reference, though that doesn’t seem actively helpful as of now.