My Minimoog Voyager Electric Blue has developed an annoying fault in the filter section that appears to be thermal, usually coming on 20 minutes after power-up.
The problem manifests itself in loud crackling noise in the filter B (right channel), like a really bad connection. It's present in the line out and headphones. The noise depends on the filter cutoff frequency; at lower frequencies it turns into a dreadful buzz, and tends to go away beyond 4kHz. Having said that, it's not an issue with the pot, as it's also triggered by the filter envelope, and infact persists when I leave the gate open. It's also there when no sources are mixed in. It's so bad it makes the synth practically unusable.
Moog alerted Voyager owners about a batch of faulty TI chips two years ago, but my EB wasn't in the affected serial number range, so this may be a different issue. I've seen some discussions on here about filter problems pertaining to the CD4052 filter pole multiplexer (U51) on the analogue board, but the noise persists when I switch filter poles. Should I be looking at this or at one of the myriad CA3046 transistor arrays that implement the filter itself?
Can anyone here (hi, Rudi!) point me in the right direction? I have basic electronics skills, a scope, and have replaced a few DIP components before, so this should be a simple DIY once I locate the fault... plus I'll learn a bit about synth design.
Any hints appreciated. Thanks and have a great week,
--GT