Elektor Formant Modular

Hi,
i finally got the old formant system repaired, and it run´s..
But from time to time the oscillators won´t "start". Means, if i 
switch off and on again, then sometimes the oscillators produces sound. 
But sometimes i need to do a retune on the "start" poti of the circuits.
Anyone else have this problem ? it´s very annoying when you don´t 
know if the system works, if you switch it on..
If i test one VCO alone, and the other two unplugged it always works.
But the psu is big enough ...

Kind regards
Wolfgang