Vintage Synth Repair

Hey list.

Well - been here before. Just had my arp odyssey back from a clean up and tuning up, and 
installment of a CV/GATE. I bought the CV/Gate from Kenton Electronics UK, and it is custom 
for the Arp odyssey (2800).

I got it back - and it works. Fantastic - but there is a problem. When the CV/Gate is in use, 
the synth is totally out of tune. If I unplug it, and play the keyboard, it's totally in tune.

Does anybody have an idea why? - and what can be done about it? 

Best,
Michael, Denmark