Vintage Synth Repair

Hi Martin

I don't know the Quadra, but I'm currently repairing an Omni. I had a couple of non-working notes in the string section (Upper Voicing Board) due to bad 4069. An oscilloscope helps a lot fixing that. Also, ARP used a lot a tantalum caps, which tend to go short while aging.
I don't like the motto "recap first" and prefer understanding before ironing, but I must admit almost half of the tantalum caps were actually bad! On the keyboard section, I replaced tants by cheaper electrolytics. I've read at that time, tants were choosen by ARP because of a better quality; modern electrolytics have improved quality and can replace tants where leak current is not critical.

HTH

Francois
--- In vintagesynthrepair@yahoogroups.com, "bluejinn" <nchevatarevich@...> wrote:
>
> Also, I had an issue with the microprocessor, here is a thread regarding that. OT I know, but it is good to have some reference material in case you have the same problem.
> 
> http://homerecording.com/bbs/general-discussions/analog-only/arp-quadra-computer-problem-325378/2/
> 
> --- In vintagesynthrepair@yahoogroups.com, "bluejinn" <nchevatarevich@> wrote:
> >
> > Do you have the service manual? This is critical. If not, you can find a partial service manual here:
> > 
> > http://www.synthfool.com/docs/Arp/ArpQuadra/
> > 
> > It's actually missing a couple of pages, (a parts list and one PCB  diagram) but is complete enough, and if you need the missing page I have it. I am pretty sure this one has all the schematics. Also, most of the other copies of the manual you will find online will in fact be this scan.
> > 
> > I am having similar problems with my Quadra, with strings/poly section on certain sharps sounding wrong, and also one note not sounding at all, and I am pretty sure these are separate faults.
> > 
> > The Quadra poly synth section is based on the Omni, (and some of the service literature actually says Omni) and I haven't got around to working on mine, but started to look at threads re: similar issues with the Omni.
> > 
> > Sorry I can't be of more help at the moment. I'm not that much of a tech either. The Omni manual is also available at that same site above and I started to compare the two to learn about how the notes are produced.
> > 
> > --- In vintagesynthrepair@yahoogroups.com, martin.morgan@ wrote:
> > >
> > > HI all,
> > > 
> > > My 1st post to this group - been lurking a while.. :0)
> > > 
> > > Quadra question for you - Top C# (C#5) and only this one note is 
> > > misbehaving
> > > 
> > > On both the Poly & Strings sections when on the 4' setting, this note also 
> > > sounds the 8' setting note
> > > 
> > > On 8' setting the all the notes play as expected
> > > 
> > > Any one come across this sort of thing before?
> > > 
> > > Also one other observation is that the keypad itself is not a Pratt & Read 
> > > - is this a common thing with Quadra's?
> > > 
> > > Hope this makes sense!
> > > 
> > > Regards,
> > > 
> > > Martin
> > > 
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