PDP 11 gear finally moved

Tothwolf tothwolf at concentric.net
Fri Jul 24 00:17:54 CDT 2015

On Wed, 22 Jul 2015, Chuck Guzis wrote:
> On 07/22/2015 10:09 PM, Tothwolf wrote:
>> One example I can give are some Pentium P55C architecture (Socket 7) 
>> systems which I've been running with minimal downtime for ~15 years. 
>> The original power supplies with their original (and relatively low 
>> quality) capacitors lasted about 15 to 17 years (I think the 
>> manufacture date code stamped on the oldest one was 1998) before the 
>> systems began to develop stability issues, requiring me to rebuild the 
>> power supplies with new capacitors. I fully expect that the 
>> replacements would last even longer than 20 years, however I rather 
>> doubt I'll be running those computers by then.
> Does anyone have much experience with the so-called "solid electrolyte" 
> electrolytics?  Fvor replacing vintage caps, they're probably not a 
> viable choice as they're mostly SMT, but just wondering...

I believe there are a few webpages out there written by people who have 
tried it. From what I remember reading about them years ago, they had no 
success when they tried to use them as replacements in switch mode power 
supplies (no surprise, since the solid polymer parts they attempted to use 
had way to low of ripple current rating for that application) but had 
better results with certain PC motherboards.

I use solid polymers as replacements in some applications, and as they 
continue to decrease in cost, I've been considering using them more for 
replacement of aging SMD aluminum electrolytics. One application where I 
particularly like solid polymers is for replacement of the vcore regulator 
filter capacitors on Pentium 4 industrial single board computers (yes, the 
P4 is still /widely/ used and extremely common in that market, although it 
is slowly being replaced by the Core Duo). The original aluminum 
electrolytics in that application are usually 6.3V rated parts while the 
solid polymer replacements are 2.5V or 4V (vcore is under 2V).

In addition to long term stability, another major benefit to solid 
polymers is that unlike aluminum electrolytics and solid tantalums, solid 
aluminum polymers they can be used at their full rated voltage with no ill 
effects. The only real downside that I know of for a solid polymer is that 
they have an incredibly low ESR (less than 0.01 ohm), which can actually 
upset older circuit designs which were not designed for capacitors with 
such a low ESR.

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