Vintage Synth Repair

I don't have any current Pro5 experience, but in synths of the day,
the CPU shared duties between reading the pots, updating the LEDs
and sound generation (to some degree).  I've seen situations where
a dirty pot (which gives out wildly varying values) caused the CPU
to spend too much time reading the pot and sacrificed the lower 
priority functions (e.g. the LEDs).  For instance, the Mirage would
totally give up on it's LEDs if you played fast chords... ;-)  


----- Original Message ----- 
From: "easterleggs" <milotoll@...>
To: <vintagesynthrepair@yahoogroups.com>
Sent: Wednesday, November 22, 2006 7:23 AM
Subject: [vintagesynthrepair] SCI Prophet 5 display flicker


> My Prophet 5 had an issue where the LED's would occasionally flicker
> slightly and introduce a glitch noise into the audio output.  I've
> since replaced all  power supply caps (tantalums replaced with
> electrolytics) and the LM337 voltage regulator.  After some initial
> tests it seems to have remedied the glitch noise problem (even though
> the LED's will flicker a bit when adjusting the FILTER CUTOFF
> pot...?), BUT (isn't there always a 'but'?!) a new issue has
> manifested.  My Prophet is a rev 3.3 with MIDI.  When in preset mode
> on any patch ending in the number 8, some LED's on unused buttons
> flicker on and off, the numbers on the panel will scramble a bit, and
> occasionally, the synth will skip into TUNE mode.  The problem doesn't
> happen when I press the PRESET button to take it to panel mode nor
> when the patch number ends in anything other than 8.  Is this a RAM
> (6508 CMOS) problem?  Anyone dealt with this before?