Vintage Synth Repair

Hi there.

Is your P5 still stable after the fix you describe here ?

Thanks!


--- In vintagesynthrepair@yahoogroups.com, "easterleggs" 
<milotoll@...> wrote:
>
> My Prophet 5 display flicker/lockup problem has been solved!  When
> replacing the LM337 voltage regulator I noticed that the screw and 
nut
> that connects the regulator to the large heat sink would not tighten
> beyond a certain point.  I thought it was snug enough and proceeded
> with my power supply cap replacement.
> 
> Upon second inspection the threads of that screw had worn away so 
the
> LM337 regulator (negative supply) was not making good contact with 
the
> heat sink.  Following the recommendations of the service manual, I
> replaced all three regulator screws with new #4 3/8" round head
> machine screws.  I cleaned the heat sink, mica tabs and regulators 
of
> any old heat sink compound.  I reapplied heat sink compound to the
> back of the regulators and to the mica tabs.  I fastened the
> regulators to the heat sink using the nylon washers, lock washers 
and
> nut with new screw prepared with a blue, medium duty threadsealer
> compound.  I tightened the screw until the nylon washer started to
> deform.  
> 
> The Prophet 5 now does not exhibit the initial flicker/glitch noise
> problem I had before changing ALL power supply caps NOR does it 
jitter
> and lockup after an initial 15-20 minute warm up.  Lesson learned:
> Don't neglect the power supply in the Prophet 5!
> 
> Thanks for all the suggestions!
> 
> 
> --- In vintagesynthrepair@yahoogroups.com, "easterleggs"
> <milotoll@> wrote:
> >
> > 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?
> >
>