Vintage Synth Repair

--- In vintagesynthrepair@y..., "Rich Nolden" <ready69@h...> wrote:
> 
> I have recently aquired an ob-8. Upon firing the bad boy up i found
> the sounds to be wierd and pots to not seem to work correctly. SO i
> downloaded the service manual and started folloing the calibration
> steps.
> power supply calibration went great got those Exact!!!
> DAC calibration had a bit of an issue. DAC Offset went ok, but i
> noticed a steady but slow voltage drop.. calibrated to 0.000v at the
> closest avg time i could.
> DAC SCALE went a bit rougher with the pot all the way counter-
> clockwise I am only able to get to 9.85v instead of 10.00v ot say to
> tune it to 10.00 +- 5mv
> 
> bend trimmers went excellent....
> 
> adjusting envelope offsets i didnt do they seemed steady (assuming i
> understood the instructions correctly
> 
> Oscillator volts per octave went very very bad....
> while checking osc1 all 8 voices light led3 but do not adjust to the
> point that 2and3 light. osc2 the lower board sometimes led3 blinks
> rapidly and sometimes it will stay on steady... the upper board led3
> blinks constantly thru all voices.....this prevents corectly being
> able to adjust the filter envelope modulation into osc2
> seems weird that both oscilators for each voice would all be 
bad.....
> 
> led test went fine
> 
> switch test hold and programmer 1 and 2 tend to blink slightly when
> pressed... probably corrosion (think i can fix that)
> 
> Pot test went bad as well... all pots seem to be erratic when using
> the led test to check the pots....
> 
> oscillator drift test.... i get lights on under keyboard double and
> upper light and under group b and d light seeming to mean that 
voice1
> osc2, voice2 osc2 voice3 osc2 and voice 4 osc2 are all bad... I am
> running the test several times to see if this is erratic as 
well.....
> 
> Now these were done using the service manual but not using eco 427
> since it refers to revision a7 and I have b5 did I do something 
wrong
> there?
> 
> I am now lost in where to go next.... how to clean pots? or do they
> have to be replaced? what can be making All oscilators run weird?
> 
> PLEASE PLEASE HELP!!!
> 
> Upon checking the oscilator drift test each time a different set of 
oscillators report bad.... leads me to believe something else might 
be wrong.....

> 
> 
> 
> 
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