[sdiy] OB-Xa Filter Fun!

[Mesa237 at aol.com]

Well, ok, the title is a bit misleading; i'm helping to resurcet a friends 
Ob-Xa.  I've had the rest of the machine working fine for months now, but the 
"upper" 4 voices are not modulating thier filter cutoff.  I can watch on an 
o-scope all of the envelopes, LFO's, CV's from the knobs... etc... but the 
filter cutoff remains quite static on all four vcf's.  i've even tried 
swapping cem chips with the lower boards; nope.  Any ideas anyone?  

Thanks in advance for any help,

paul
(who feels like a schlep asking such a desperate question, when he's only 
responded to others' three or four times in the last several years)