[sdiy] Debugging problem with 4-track

Michael E Caloroso mec.forumreader at gmail.com
Sun May 27 01:05:14 CEST 2018

Heat plays a primary role in how long capacitors - or most components
for that matter - last in their life.

"20 to 30 years" is hardly a basis.  I have a British guitar amp with
the original caps dating back to 1963 and my amp tech said they were
fine.  And he has been working with guitar amps for over forty years.


On 5/26/18, Pete Hartman <pete.hartman at gmail.com> wrote:
> On Sat, May 26, 2018 at 5:25 AM, Corey K <coreyker at gmail.com> wrote:
>> That's interesting, because I've read in several different places that
>> electrolytic capacitors dry out after 20 to 30 years, and often need
>> replacing. Is that false?
> "It Depends"
> It is true that electros do dry up, but there is no point in replacing
> every single capacitor in a piece of gear "just because".  If you have
> evidence of a malfunction, as you do, you trace down the cause and then
> take appropriate, targeted action.  Bulk changes trying to troubleshoot
> with a shotgun, as Gordon said, are likely to cause more problems.
> Observe the state of the caps.  Are the electros bulging?  Leaking?  Then
> replace them (and clean the board if there's leakage).  Are other types of
> caps discolored, like they were getting too much voltage?  Then replace the
> ones that look burnt.
> But more importantly: is the PSU putting out the rated voltages?  What's
> different about the voltage output when you use 7.5V vs 12V input?  Does
> the voltage change when you attempt to press the record button?  How about
> with batteries, how does it behave with them?
> Answers to those questions will focus you in on components that actually
> need changing.  And perhaps they are the electros or other caps in the PSU
> section.  But blind guessing doesn't usually fix much.
> The other caveat here is that there are some synth techs who swear by
> re-capping.  So note that all this is my opinion as a troubleshooter, but I
> don't have the same experience.  However, that experience of those other
> techs will usually give them some intuitive sense of how likely a given
> synth is to have those kinds of faults, so a re-capping by someone who's
> been doing this for 10-20 years is perhaps more justified than one by
> someone with little or no experience who's just trying something because
> they heard it's what you do.
> "Oh yeah, I remember that other oberheim, the caps they used were crap, we
> better just go ahead and replace these" does have some basis in likely
> faults.  "I better replace all the caps in this gear because someone once
> told me that's how they fix things" does not.
> Pete
> PS: the bulk of my experience is troubleshooting and repairing medium to
> large computer equipment, mostly by Sun Microsystems.  I really wish I
> could get back all the hours lost when a customer said "there was a single
> correctible memory error, you must replace ALL THE DIMMS" and then the
> situation cascaded into additional faults because the machine was touched
> unnecessarily.

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