Vintage Synth Repair

On Monday 13 April 2009 05:53:45 pm John LeVasseur wrote:
> NOT the best advice dude.
>
> Electrolytics capacitors have a very specific shelf life, whether charged
> regularly or otherwise. The chemicals breakdown over time regardless of
> use. Since most MS-20's are approaching 30 years of age or more, most of
> them have exceeded this time period, by about 5 years. Electrolytics do not
> only exist in the audio, but also play a role in control and timing of
> circuits, so lack of bottom end end is only one small symptom. Also a bad
> electrolytic may not show sign of leakage.
>
> Furthermore, a mini recap in the audio chain only and VCF section, is the
> most intrusive choice sonically. It also wouldn't address the issues in
> this situation.
>
> His problem sounds to me to be a cap related one, since there is a time
> factor in the problem. Sounds to me like the caps are becoming weak
> chemically are are taking longer to charge to full capacity.
>
> Most vintage synths from the 70's and early 80's are at the end or way past
> their life in terms of electrolytics. Once you reach 25 years in age that's
> pretty much it, used often or never is irrelevant.
>
> That's coming from an MSEE.
>
> just my twocents

Chemicals breakdown?  Can you point me toward any place that documents such 
stuff?  First I've ever heard of this,  and I'm pretty dubious about the 
whole recap thing to start with,  if it's not needed.

This coming from a tech for four decades or so...

> --- In vintagesynthrepair@yahoogroups.com, "thirteentech" <thirteentech@...> 
wrote:
> > > Oops, my post should have read "PCB contamination" not BCB
> > > contamination. The issue of re-capping does come up a lot, and both
> > > answers are true - many caps get replaced unnecessarily, and many
> > > machines are also laboring under a load of bad electrolytics.
> >
> > Some reasons to replace electros in very old machines are:
> >
> > Obvious leakage.
> > Obvious lack of bottom end response.
> > If the machine has had periods of years where it has not been powered up.
> > Electro's need voltage across them to keep them properly formed.
> > Situations where the model is known to be reaching the end of it's cap
> > life, and as far as I have seen, Korg PS and MS series are definately
> > there. Caps that are being overheated, such as those mounted next to
> > heatsinks and power resistors.
> >
> > Reasons NOT to replace electro's:
> >
> > If the caps are high quality, such as Spragues, and are in machines that
> > have been kept in service. Outboard gear in large studios is a good
> > example.  IN this case, removing a few caps and testing capacitance and
> > ESR would be the obvious thing to do, and if they are still in spec, and
> > the machine sounds good, then I would say leave it alone and re-test
> > every 3 years.
> >
> > The other option, is a "mini-re-cap" where you replace the caps in the
> > audio path and VCF's only with high quality audio grade electrolytics
> > such as Panasonics.
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>


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