Vintage Synth Repair

>>I have a problem with a Cheetah MS6 snyth. Some of the tones have
missing or weak notes randomly placed on the keyboard. When I reselect
the same tone the missing/weak notes move position on the keyboard.
Not all the tones do this only a small number but it is always the
same tones.<<

david- sounds like you have a bad (3396) voice chip or two. the
problem is "moving around" because the synth assigns the next
available voice to each note you play. it also sounds as though only
certain waveforms are affected. 

I'd suggest you do a little more detective work to narrow it down,
then when you can either get the lid off or take it to a tech, you can
say "it's the sawtooth on voice 5" or whatever.
do you know how to create six monophonic parts in performance mode? 
I have found that setting the "number of voices" parameter for each
part to "one" over-rides the dynamic voice assignment & "hardwires" a
voice to a part.
put them on different midi channels. make yourself some patches that use 
1) osc A square only
2) osc A sawtooth only
3) osc B square only.....

you get the idea. then try these patches one by one in your 6-part
multitimbral performance & play each one in turn until you hear the
weak/faulty voice. I have one ms6 with a voice 4 that will not do
square waves anymore. since I was mainly using the ms6 as a
multitimbral monosynth, I could force this voice to do something else
(the white noise still worked) until I could do something more
positive about it. (I have the replacement voice chip I need, but have
been using a second ms6 instead due to time-pressure).

anyway. however well you get on, I should also recommend that you look
at kris maad's ms6 site. his revised firmware is superb- it allows
full CC control of any ms6 parameter over midi. he will sell you an
eeprom with his new firmware on it, & it's worth every penny. he may
also still have some spare 3396 voice chips, though these are in short
supply like much of the curtis chip library these days. in any case,
you will either need a tech or need to be one to sort this out.

let us know how you get on.

duncan/r.m.i.