sh-09 oscillator wackiness.. can I repair?

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monk_volcano
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sh-09 oscillator wackiness.. can I repair?

Post by monk_volcano » Sun May 15, 2016 6:23 am

Hi there.. I have an SH-09 with some issues.

The tuning is very unstable. Sometimes it will hold tune for quite a while.. maybe 30 minutes or so, but usually it is wobbling all over the place. another thing I have noticed is that moving just about every slider will nudge the pitch around. Very strange. Also, even when the lfo is not modulating anything, It will modulate the pitch ever so slightly.

Some people have suggested this is leaky capacitors. I'm pretty handy with a soldering iron and I was thinking about replacing some myself. How would I go about doing this?

Also worth noting, my father is adept at electrical stuff. He was an appliance repairman and he's worked on home stereo stuff.. however it's hard to wrangle him for help these days. I feel like if I could tell him more specifically what I need to do, he could make sure I didn't screw it up.

thanks everyone.

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Re: sh-09 oscillator wackiness.. can I repair?

Post by sam » Tue May 17, 2016 9:25 pm

i would suggest changing the coupling caps on the power supply first....while your there you might as well replace all the caps on that board...
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Re: sh-09 oscillator wackiness.. can I repair?

Post by Werecow » Tue May 17, 2016 9:44 pm

At ~35 years old, it's not a matter of -if- caps are going, but which ones. As sam suggested, I'd start in the power supply. The C45 & C46 filter caps take the most abuse and tend to dry out, so I'd replace those first and see what effect it has.

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Re: sh-09 oscillator wackiness.. can I repair?

Post by monk_volcano » Wed May 18, 2016 6:30 pm

thanks guys. So if indeed it is the caps in the power supply, then I'm guessing what's happening is the other circuits on the synth are getting really inconsistent voltage and that's what's causing all the wobblyness?

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Re: sh-09 oscillator wackiness.. can I repair?

Post by Werecow » Wed May 18, 2016 9:16 pm

That's one distinct possibility. Noisy power supplies would have effects "across the board", as you've guessed. Even if it doesn't completely get rid of the instability, replacing those caps is just good practice with equipment that age. BTW, be sure to observe the correct polarity when replacing them. When installed backwards, they tend to get very, very unhappy, and very, very quickly (think minor explosions and confetti).

Others here have more experience with the SH-09, so they may be able to point to known failures specific to that model, if you still have problems with it.

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