Xpantastic!

Hi everyone, my xpander seems to fail the VCO tune test randomly!some
voices fail during one test and pass on the next! there is no
cosistancy on the voices that fail,it can be any one of them!Some
times(rarely) the vco test passes! I have the same problem sometimes
with the Resonance and VCF but not as often!
I have totally rebuilt the power supply,changed the battery and output
bypass capacitors!All currents measure right so this is not a voltage
supply problem!
The only other part I can think of is the DAC or maybe the Timer?
Any thoughts?
Takis.