Vintage Synth Repair

That could explain the more noticeable flicker witnessed when the
FILTER CUTOFF knob is adjusted though there's no audible evidence of a
dirty pot.  Of course, it wouldn't hurt to clean them all anyway!

But the other problem I described -a more dramatic flicker in PRESET
mode with any program ending in "8"- has me concerned.  Perhaps
there's some intermittent short in the switch caused by some some bit
of loose metal...?  

I'll explore some more possibilities...

--- In vintagesynthrepair@yahoogroups.com, "GB" <grantbt@...> wrote:
>
> 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?
>