Vintage Synth Repair

Hi there,

this is my first post to the group and I would like to ask you a 
Oberheim related question.

I own an old Oberheim OB-8, whose voices are not functioning
properly. 
With the help of the downloaded service manual I checked for the 
oscillator calibration and found out, that one or more VCO's do not 
function properly.

The manual
( http://home.swipnet.se/cfmd/synths/companies/oberheim/ob8-sm-8.jpg )
 reads like this:

"If both test LED's are off, or seem to be flashing randomly, then 
this oscillator is not functioning properly and should be repaired or 
replaced."

Does anybody know, HOW I can repair a malfunctioning Oberheim voice 
oscillator? Which parts (IC's) must I replace?

You can find the service manual, schematics, parts-list etc. at 
http://home.swipnet.se/cfmd/synths/companies/oberheim/

Thanks for your help,

Randy.