Vintage Synth Repair

update!

i didn't even realize it but "c2" the capacitor hooked to pin 1 and 8
of the op amp is totally broken. classic newbie move i guess. fix one
problem and cause two more. so now i'm looking in the user manual and
i don't see a value for that part in the parts list of board C-1. do
you happen to know what the value of that component is?

thanks again,
johnny


--- In vintagesynthrepair@yahoogroups.com, "cockandswan"
<cockandswan@...> wrote:
>
> 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@yahoogroups.com, 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@
> >
>
----------------------------------------------------------------------------
> > "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)
> >
>
----------------------------------------------------------------------------
> >
>