Vintage Synth Repair

one hundred percent man! thank you so much for the help, but now i
have created another problem! i was cleaning these super sticky
sliders with isopropyl alcohol and i think i might have changed the
value of the pot that controls the cutoff frequency. now the minimum
cutoff is like half of was it was. it won't do any muffled sounds
except maybe on the down stroke of the lfo modulation.

how likely do you think that is with these old parts? could it be
something else? maybe the value of op amp changed something? i did
melt part of the capacitor that is directly to the side of the op amp
i replaced and part of it is exposed. could that have cause the change? 

i'm taking some electronics classes and this arp seems like it'd be a
great way to do some projects. maybe my next project shoudl be to just
replace all the sliders? 
any other advice on cleaning sticky sliders? (i might make another
thread just about this subject a little later!)

thanks again for such a fast and helpful response,
-johnny

--- In vintagesynthrepair@...m, Malte Rogacki <gacki@...>
wrote:
>
> > none of the modulation to the filter works and the filter is really
> > scratchy.
> 
> OK, first of all you identify on which board the filter is on and
look at
> the appropriate schematic section.
> In this particular case it's board C (or C-I in the schematics).
> 
> Now, this whole problem looks pretty straightforward to me. Let's
see if we
> can identify possible culprits.
> 
> When looking at the schematic we can see the various modulations sources
> for the filter all on the left side. They pass through the slider
> potentiometers P10, P11 and P12 and then pass through A1 (an LM301
opamp).
> So first I would measure (with an oscilloscope) if something comes
into the
> opamp (for example try the LFO); and then if it again leaves the opamp.
> 
> That's pretty much the modulation path before it reaches the filter
module;
> if a modulation signal comes out of A1 we have to look elsewhere.
But this
> would be my first "suspect".
> 
> -- 
> Malte Rogacki gacki@...
>
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> "Don't forget to TURN ON THE SYNTHESIZER. Often this is the reason
why you
>  get no sound out of it." (ARP 2600 Owner's Manual)
>
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>