Archive of the former Yahoo!Groups mailing list: 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