PDP 11 gear finally moved

Peter Coghlan cctalk at beyondthepale.ie
Tue Jul 21 13:58:00 CDT 2015

Rich Alderson <RichA at LivingComputerMuseum.org> wrote:
>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.
>                                                                Rich
>[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

Hi Rich,

Thank you for providing further clarification but please understand that I was
trying to give you an opportunity to get out of the hole you were digging, not
trying to encourage you to dig deeper.

I was hoping to avoid going back over the issues which have been previously
debated at length on the list without reaching any conclusions other than that
different people have different strongly held views on the subject but I guess
that was too much to hope for :-(

Peter Coghlan.

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