[sdiy] MKS-30 Voice "one" acting weird

[Csaba Zvekan]

Hi  Group,

I have this Roland MKS-30 to where one VOICE (Voice 1) is acting weird :
The machine works perfectly until 15 to 20 minutes pass then for that  
particular voice the VCF sounds like you would have "VCF Reso"  full  
up/ high. And later the Voice would even mute.			
I have replaced the three OP-AMPs 4558 in VOICE 1&2 and a four of the  
100uF capacitors in the Power Rail. Also quickly replaced the 6800uF  
and the two 4700uF Capacitors in the Power Supply ... while it was open.
Now I am suspecting the 0.22uF and 0.47uF and 10uF BiPolar  
Capacitors . Which I didn't have at this point.
I think the mute part of the VCA is finally gone. But still a  
crackling sound and the VCF resonance problem is still there.

My question is this: As of right now I am guessing around rather than  
measuring and knowing. Can somebody give me some input on how I might  
determine my problem. Should I just compare Voice 3's Audio path with  
the Voice 1s and then narrow things down . Or does anybody already  
suspect what might be my problem.
I think it must be in the VCF/VCA section of VOICE 1 and narrows is  
down to a couple of op-amps ,diodes , bipolar caps and the all mighty  
AIQH800170.
I hope that one is OK. Anybody got some sources for that ROLAND custom  
chip ?


Any hep greatly appreciated

Csaba