Vintage Synth Repair

Right where do I start,

My little AXXE (mk2 black and orange) seems to having a strange envelope
problem. When you turn the arp on, and its set to S and H with the keyboard
trigger repeat set, the envelope section works as normal following the LFO
speed. After about 15 seconds or so it starts to drop out in a very slow osc
type of way (very vague I know). The volume drops and everything starts to go
out of tune etc then returns to normal and then back again.
At this point there normally is a tone which is on tone lower than the lowest
key.
When you play notes straight on the keyboard it does the exact same thing and
it appears to be some sort of component break down somewhere on the trigger
section. The keyboard intermittently stops working too and the CV gate sockets
won't work.
Its been to my repair man who needs schems, nothing is obviously knackered but
he's at a lose without more data.

Thanks for reading this rubbish and all the best to you list guys.

B