[sdiy] Korg Delta problem

Dave Brown davebr at modularsynthesis.com
Tue Jun 19 04:28:53 CEST 2018


I rarely replace capacitors unless they test bad.  If I have an electrolytic
in a product that is 30 years old, I don't have any confidence that the
capacitor I might replace it with will last even 10 years.  Now if it is a
tantalum, then that is another story.  At the vintageTEK museum we regularly
have to replace tantalums and all the black beauty and bumble bee caps.
Those do go bad.  I always chuckle at the people who salvage black beauty
and bumble bee capacitors and sell them to people at $20 each so they can
get that "vintage" sound.  Those are all bad.

I get a lot of repair items in the shop where the owner went through and
replaced all the capacitors which was generally unnecessary work.
Occasionally someone will ask me to as part of a repair and I usually try to
talk them out of it, but I have relinquished and replaced some entirely
knowing it is just wasted dollars.

Every decade does seem to have its story of bad capacitor lots.   I have
some vintage radios back to the 1920s that still have original capacitors in
them.  Of course all of this technology generally predates synths.  I still
stand by my tin oxidation suggestion.  People want to send me synths to
repair and I ask them to reseat all the parts and most of the time that does
it.

Dave

> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of
> Gordonjcp
> Sent: Monday, June 18, 2018 4:00 PM
> To: synth-diy at synth-diy.org
> Subject: Re: [sdiy] Korg Delta problem
> 
> On Tue, Jun 19, 2018 at 12:45:31AM +0200, sleepy_dog at gmx.de wrote:
> > Gordonjcp wrote:
> > >On Mon, Jun 18, 2018 at 10:01:45PM +0200, Jean Bender wrote:
> > >>thanks !
> > >>you mean the caps from the power supply ? How could the power
> supply
> > >>only disturb or make no functionnal only half part from the synth ?
> > >You'll never find "bad caps" in a synth.  They're pretty much a myth.
> > >
> > How so? Is it a myth that electrolytic caps will chemically degrade?
> 
> Yes.  You might see them fail if they've been thoroughly hammered in
> cheap badly-designed switchmode power supplies.
> 
> > I have been told by more than one EE not to bother using
> > electrolytics that have been laying around for 5 years, not just for
> > things requiring low ESR, not for anything.
> 
> Horseshit.  If you believe that, I've got some lovely speaker cable to
> sell you, complete with lithodynamic vibration mass compensators.
> 
> > I don't have any numbers. But even in some simple old synth PSU with
> > a pair of fat caps and linear regulation, it would be bad if those
> > caps got a huge ESR and reduced capacitance, no? Now I can imagine
> > that this is considered in the circiut designs, but only so much?
> 
> They won't get "huge ESR and reduced capacitance" though.
> 
> The electrolyte isn't milk.  It doesn't go off.
> 
> There is so much utter bollocks talked about capacitors, it's absolutely
> mindblowing.  In 30-odd years I've replaced less than a dozen faulty
> electrolytics in (what feels like) thousands of pieces of equipment.
> 
> People are obsessed with this idea that every fault is "bad caps".  It's
> never a capacitor.  It's always something else, although I'll grant you
> in most linear power supplies it's the rectifier diodes which fail and
> *then* take out the big electrolytics.
> 
> It's got to the point where I won't touch anything that's been
> "re-capped".  I just assume that if it's been "re-capped" and it's still
> not working, it's now beyond repair.  It was probably a simple fix
> before the poke-and-hope brigade got their grubby mitts on it.
> 
> --
> Gordonjcp
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