[sdiy] Prophet 600 problems..

[Bob Weigel]

A guy wanted me to sell this for him but it has problems.  Like new 
looking later serial number.  5900 ish.  Anyway when we powered it up 
here it wouldn't allow any knob edits.  And occasionally would lock up.  
Always locks up if you hit the sequencer button.  I noted that moving 
the mod wheel would unlock it sometimes!  Weirrrddd.  Anyway I get 
inside and it all looks ok but there is ...from the 4067 chips on the 
front panel, just 2 V peak jibberish signals.  Both of them are doing 
the same thing.  All the analog knob voltages look fine on the inputs 
and the address lines and 5V all look good. Hmm.. and grounds is making 
good connection also.  So I'm quite puzzled ..anybody else seen these 
chips fail in that mode?  They're just showing a 2V flat line with 
periodic rapid ground drop and jagged rise back to 2V..