[sdiy] Caps in synths... was Re: [AH] Arp Solina with excessive chorus noise

[Pete Hartman]

First, I agree that I am not in the "re cap just cos" camp.  Look for
something actually wrong, don't guess.

However, I have seen electro caps fail in synths, and other types of caps
as well.

One of my first repairs was a Roland S-10 sampler that had bad Mylar caps
in the supply section.

Another, I believe I may have discussed in this list, was an XP-50 where
some smd electros in the later signal path had leaked crap on the boards
and had terrible hiss in the output.

Now, those may have been cheap junk, but given the general pressure to
reduce cost, I don't know that we can make a priori assumptions that any
given synth is made with all high quality caps.

Neither example is a "classic" of course, but I think the general principal
applies.

TL;DR version: caps do fail in old synths.  Dismissing the idea out of hand
is no more sensible than the urge to re cap everything.

Thanks

Pete
On Jan 31, 2016 5:51 PM, "Michael E Caloroso" <mec.forumreader at gmail.com>
wrote:

> I don't subscribe to the "re-cap" club.  Very rarely does it fix
> anything in synths or string machines.
>
> Electrolytics do fail, but usually when subjected to high heat.  Think
> guitar amps and power amplifiers.  Not synths.  Lots of myths from the
> guitar world propagate to the synth world.
>
> Solina did not use a commander for the BBD circuits.  That is the
> accepted technique to reduce noise in BBDs.
>
> MC
>
> On 1/31/16, Gordonjcp <gordonjcp at gjcp.net> wrote:
> > On Sun, Jan 31, 2016 at 10:26:04PM +0000, Chris Juried wrote:
> >> Agreed, Tom. Strap an ESR meter to those caps and watch the resistance
> >> shoot up. Replace them and watch you AC ripple fall.  Sincerely,
> >
> > Unlikely.  Except in cheap crappy switched-mode power supplies,
> > electrolytics just don't fail.  Maybe if you're working on equipment that
> > was built in and has not been switched on since the 1950s or 1960s, you'd
> > have a problem.
> >
> > In roughly 30 years of repairing electronic equipment I've replaced maybe
> > half a dozen genuinely faulty electrolytics (save the aforementioned
> cheap
> > crappy SMPSUs - if I never see an Amstrad satellite TV receiver again
> it'll
> > still be too soon).  Disc ceramic and tantalum bead capacitors are a
> > different story altogther.
> >
> > Incidentally, I automatically charge an extra 300 quid to even carry
> > something that's been "re-capped" in from the car, never mind take the
> > screws out.  Every single piece of equipment I've seen that has been
> > "re-capped" has had significant faults, made worse by the "HERP DERP IT
> NO
> > WORKY MUST BE CAPACITATORS" mentality that leads people to fuck about
> with
> > the insides blindly.  Generally it takes a full day of work to get
> anything
> > "re-capped" to even run at all, never mind correctly.
> >
> > Never, *ever* "re-cap" things.  If it has a fault, fix it.  It won't be
> an
> > electrolytic capacitor.
> >
> > --
> > Gordonjcp MM0YEQ
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