[sdiy] Repairing a Crumar Stratus...schematics?

[Robert Weigel]

Hmm.  I have trilogy schemos at home and I think there are lots of
similarities in that section probably.  This uses the CEM3330 vca's and
the CEM3310 eg's like the trilogy I'm sure.  I think they're the same but
just no string section on yours.

So anyway first on my trilogy there are presets and number 1 is knobs. 
Knobs have no effect if other presets are selected.  Hmm.  Nevermind. 
Just went to my page and found a pic on synthmuseum from there.  It has no
presets I guess.  Ok so knobs should always be active then. So if the
filter is closed all the time it's likely either a problem with the filter
control circuitry or...probably what it is is an offset op amp somewhere..
check the amp that sums control sources for the filter control.  EG amount
would be one of it's inputs but if the thing is just low all the time it's
probably an offset condition on the op amp that sums all the control
sources.  Let me know if you need more help when I get home on Tuesday or
so. Just sweep output pins on op amps in that area though and I'll bet
you'll find it. -Bob
> Hi everyone,
>
> I just bought a very very heavy (18 KG) Crumar Stratus synth that has some
> problems. I already fixed some of them and I calibrated the synth (alot of
> trial and error, since I don't have the service manual, but now I know
> what
> all the trimmers do).
>
> A couple of problems still remain:
> - The range of the Envelope Depth is not right. If it's set to 0 (middle)
> with the Cutoff knob entirely open the filter is still closed and there
> doesn't seem to be a way to correct this with a trimmer. Very strange. The
> Envelope Depth gets the +15 and -15V and the wiper takes a voltage in
> between those two according to the position of the knob. So the input
> voltages are ok, but somewhere in the circuitry the filter just isn't open
> enough.
>
> - The range of the Coarse Tuning is very small...like 2 semitones. I like
> it
> to be (and I thing it should be) like + and - 5 semitones.
>
> - The pitchbender VCF modulation is not working (but the normal LFO vcf
> modulation is).
>
> - Some knobs (filter cutoff) really crackle alot when I move them. They
> haven't been used for years I think and they are dusty. Usually the
> problem
> goes away when you simply turn it alot (with others synths I repaired) but
> here it doesn't. What's the best stuff for cleaning pots (it's an open
> casing)?
>
> These are the problems I was hoping to get solved....but that's really
> hard
> without the schematics? Does anyone have them?
>
> Greetings,
>
> Rutger
>
>


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