PDP 11 gear finally moved

Rich Alderson 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
> stands?

This is the policy of Living Computer Museum.  It is based on the cumulative
experience of multiple very senior electrical engineers[1] 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%
of rating.

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.


[1] 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.

Rich Alderson
Vintage Computing Sr. Systems Engineer
Living Computer Museum
2245 1st Avenue S
Seattle, WA 98134

mailto:RichA at LivingComputerMuseum.org


More information about the cctalk mailing list