PDP 11 gear finally moved
RichA at LivingComputerMuseum.org
Mon Jul 20 17:46:43 CDT 2015
From: Peter Coghlan
Sent: Saturday, July 18, 2015 1:27 AM
> Rich Alderson <RichA at LivingComputerMuseum.org> wrote:
>>> It is generally a good idea to re-form electrolytic capacitors in power
>>> supplies, and to bench check the power supplies (under some kind of
>>> load) before actually applying power to the whole unit.
>> It is always a good idea to replace electrolytic capacitors in power supplies.
>> The rest of the advice is sound.
> Can you please clarify if this statement represents the policy of the Living
> Computer Museum or is it something more personal? Perhaps some qualification
> or a re-phrasing would be useful as it does not appear to make sense as it
This is the policy of Living Computer Museum. It is based on the cumulative
experience of multiple very senior electrical engineers doing restorations
here, in conjunction with industry white papers with tables of decay rates for
the aluminum electrolytics that indicate that, *no matter what*, they lose
capacitance over time, until c. 14 years from manufacturer date they are at 10%
When, in 2004, we first began restorations of the systems that eventually
became LCM, we followed the sage advice of those who described how to "re-form"
electrolytic capacitors. Months of frustrating results eventually led to the
search for industry literature on the topic; the result of that research was
the formulation of our policy regarding this practice--that it is not worth the
time and effort for minimal results.
> I think you may have seen or participated in some of the many discussions we
> have had on this topic on this list? In light of these discussions, I find it
> hard to see how a categorical statement such as this one could be justified.
Since the proponents of this practice make categorical statements with no
evidence that they want to listen to reasoned explanations, I long ago gave
over trying to convince them, and simply respond when someone makes a statement
to a newbie which will result in frustration and failure for the unfortunate
recipient of this advice.
 NB: I am not now, nor have I ever claimed to be, a hardware engineer of
any stripe, and more particularly not an electronics specialist. I am,
nonetheless, capable of reading and understanding research papers with
statistics that back up the claims being made even if I could not devise
the experiment to test them. I rely on my colleagues who are experts to
assure me that the writers are not smoking crack.
Vintage Computing Sr. Systems Engineer
Living Computer Museum
2245 1st Avenue S
Seattle, WA 98134
mailto:RichA at LivingComputerMuseum.org
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