Discussion about the Korg PolySix synthesizer

Hi,

Here's a nasty KLM-367 problem which has been sitting on the bench 
for the last couple of days, whilst I scratch my head. I repaired the 
board orginally after the battery blew up a couple of years back. All 
worked find until the a couple of weeks back when I lost control of 
the patch banks. I redid all of the wire links, but same problem. 
Eventually I found that the clock source was missing. X1 has sheared 
off a leg so I replaced it with a 6Mhz ceramic resonator. Now the 
patch bank switches all function corectly. I can even play my patch 
bank wav files at the thing and watch the LEDs 1-8 strobe as the data 
is read in. However, I seem to have lost control of the VCF and EG 
settings. The octave, waveshape and sub-osc all work, which is a 
start. I picked on the attack pot through to pin 4 on IC34 to see if 
I could work out what was going on. The output from mux IC1 on KLM-
370 seems to swing around 0V +/- depending on the position of the 
pot. This output feeds the non-inverting side of comparator IC6 which 
presumably sets an interrupt on T0 of the micro-controller (IC22) to 
let it know that someone has changed one of the pot setting. This 
input is compared to the output the D-A converter IC33. Unfortunately 
pin 1 of IC6 always remains swung one way at -15v. To make matters 
worse the output from the D-A converter never seems to change from 
0.99v despite the database changing state. Have I still got a 
corroded or broken track somewhere? Have I got a failed D-A 
converter? Does any of this sound familar? Any thoughts or input 
would be much appreciated.

Cheers,
A