On Mon, 20 Jul 2015 23:14:36 -0600 Eric Smith <space...@gmail.com> wrote:
> On Mon, Jul 20, 2015 at 4:46 PM, Rich Alderson > <ri...@livingcomputermuseum.org> wrote: > > 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. > > That's very interesting. I haven't seen those white papers, but the > "no matter what" must in fact depend on something, since on the PDP-1 > Restoration Project we found that most of the 40 year old aluminum > electrolytic capacitors still met their original specifications, > including capacitance within rated tolerance. Of the few electrolytic > capacitors that had failed, the problem was a catastrophic failure, > not the capacitance being outside the rated tolerance. > > In the PDP-1, we preferred to keep the original components as much as > possible. Had there been a capacitor, the failure which would have > caused extensive damage to other components, we would have given > serious consideration to replacing it. However, that was not the case > for any of the capacitors in the PDP-1. > > Had our analysis indicated any expected benefit to replacing all of > the electrolytic capacitors, we would have done so, and bagged and > tagged the originals similar to what we did with failed components, so > that they could be replaced if it ever was desired to return the > artifact to its pre-restoration condition. > > I'm not recommending against LCM's policy, but I also wouldn't > necessarily encourage anyone to adopt it, nor to adopt the practices > of the CHM PDP-1 Restoration Project, without studying the issue. As Eric, I'm a member of the PDP-1 Restoration Team. The PDP-1 restoration was completed in 2005 - and annually we check the power supplies for voltage, ripple, etc. Not one of the re-formed capacitors have failed in the ten years since the completion of the restoration. I also re-formed all P/S capacitors in my PDP-8/S in September, 2013. Not one has failed since... Same with my EAI TR-20 Analog computer. And so it is for all the systems in my collection... IMHO, these "white papers" indicating that ALL aluminum electrolytic capacitors decay is obvious nonsense - based on real life experience - not someones theory... Lyle -- 73 AF6WS Bickley Consulting West Inc. http://bickleywest.com "Black holes are where God is dividing by zero"