24 Apr
2011
24 Apr
'11
12:04 p.m.
Yes, one can get lucky that way - and I have machines in my personal collection where I
have not replaced the filter caps (yet). Component tolerances can allow continued
functioning even with significantly degraded components. But if I turn one of those
machines on and it doesn't start up, that's my problem. If I turn the key on one
of our machines at work, in front of a crowd of people, and it doesn't start up,
that's a different story.
Industry studies (work by Cornell Dublier) show that aluminum electrolytic capacitors have
a limited life span. (The most common failure mode is not drying out, it is elevated
ESR.) Then there have been the various scandals about substandard components. I think it
bears consideration that electrolytic capacitors are not one of the most reliable
components in our information systems. --- Ian
________________________________________
From: cctalk-bounces at classiccmp.org [cctalk-bounces at classiccmp.org] On Behalf Of
Tony Duell [ard at p850ug1.demon.co.uk]
Sent: Sunday, April 24, 2011 11:10 AM
To: cctalk at classiccmp.org
Subject: Re: new here
cautious sort, disconnect the filter caps and perform
a leak-down test, rep=
lacing parts that fail. If you're really cautious, just replace them - tha=
t's what we do with power caps if they're over twenty years old. There's a=
date code on the part. =20
If I did that, I'd have replaced every capactior in every machine I own,
including the machine I am currently typing this on. I haven't. In fact
many of my machines, including ones that are 40 years old, are still
runnign with all their original capacitors.
Yes, capacitors fo fail. I've replaced a number over the years. And they
can fial from just old age if the electrolyte dries up. But in m
experience it's not the problem that some people claim it is.
-tony
24 Apr
24 Apr
12:32 p.m.
Yes, one can get lucky that way - and I have machines in my personal collec=
I must have been exceptionally lucky, then. I think all my HPs, all my
Philips machines and all my PDPs have their original capacotrs. Oh wait a
second, I did haev to repalce _one_ in the PSU of the 11/44.
tion where I have not replaced the filter caps (yet).
Component tolerances=
can allow continued functioning even with significantly degraded component=
s. But if I turn one of those machines on and it doesn't start up, that's =
my problem. If I turn the key on one of our machines at work, in front of =
a crowd of people, and it doesn't start up, that's a different story. =20
Sure. You have to consider what hte 'loss' is if it fails in use. This
may be in terms of lost time/profits, it may be in terms of damage ot
other components, etc.
It's like the comment we had a few weeks ago that desoldering an IC will
reduce its reliability. This is probably true, but as I said at the time
it's not something I've ever noticed, and I've desoldered and refitted
many ICs. In one of my classic machines it doesn't matter id an IC fails
a little beofre it otherwise would have done. Dor something
safety-critical, or whatever, it wouldn/
Industry studies (work by Cornell Dublier) show that aluminum electrolytic =
capacitors have a limited life span. (The most common failure mode is not =
Sure, and I undersntad the reasons for it. But I am not convinced it's
tyhe problem that some people make out.
drying out, it is elevated ESR.) Then there have been
the various scandals=
about substandard components. I think it bears consideration that electro=
Said scandals tend to involve relatively modern components, not the ones
I am talking about.
lytic capacitors are not one of the most reliable
components in our informa=
tion systems. --- Ian=20
I don't know....
Certainly Iv'e replaced many more 2114 RAMs than electrolytic capacitors
over the years.
-tony
12:51 p.m.
On 24 Apr 2011 at 12:04, Ian King wrote:
Industry studies (work by Cornell Dublier) show that
aluminum
electrolytic capacitors have a limited life span. (The most common
failure mode is not drying out, it is elevated ESR.) Then there have
been the various scandals about substandard components.
I'd also add, at least in the case of consumer devices, crappy
designs leading to operation at elevated temperatures. I can show
you units where electrolytics are hot-glued to heat sinks. Inverters
and power supplies for LCD monitors are some of the worst examples.
And then there's the sealed DC "wall wart" power supply.
--Chuck
25 Apr
25 Apr
10:49 a.m.
On 24 Apr 2011 at 12:04, Ian King wrote:
Err yes :-(. Fortunately many older classic computers don't have stupid
design featuers like that.
Industry studies (work by Cornell Dublier) show
that aluminum
electrolytic capacitors have a limited life span. (The most common
failure mode is not drying out, it is elevated ESR.) Then there have
been the various scandals about substandard components.
I'd also add, at least in the case of consumer devices, crappy
designs leading to operation at elevated temperatures. I can show you units where electrolytics are hot-glued to heat
sinks. Inverters
and power supplies for LCD monitors are some of the worst examples.
And then there's the sealed DC "wall wart" power supply.
I think you all know my views on wall weats. I hate them. I prefer to
make my own PSU in a properly earthed metal case with fuses on mains and
output side. And with the electrolytics put in a sensible place.
Some wall-wrts over here are screwed together, often with non-standard
screws. I have a PSU for one of my machines that was assembled iwth
System Zero screws down deep holes, and is thus impossible to dismantle
non-destructively without the right tool (which you don't find in every
tool shop...). Onee I'd got it open, I found the only problem was a
blown fuse, a normal 20mm cartdirge fuse in clips on the PCB with the
silk-screen indicating the type/rating to use. Very easy fix once I'd got
the screws out.
-tony
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