wrote:

On Apr 29, 9:56 am, "Michael A. Terrell"
wrote:
Tim wrote:

"Karl Townsend" wrote in message
tanews.com...
I now have four metal mangling machines that need the venerable ISA slot to
operate... These computers are not available new anymore and the new parts
route is about gone too.

I'm settling around one motherboard, CPU, memory, video card combination.
Makes it much easier to maintain. I can do an entire computer swap in
minutes if trouble happens. Or test one component at a time in a spare
test computer.

lets say I'd like to run these machines another 20 years. How many spares
am I likely to need? I'd like to buy them up now. (Note: I don't think I
need to do hard and floppy drives yet - still a lot of these around)

Karl

It's nothing more than a wag, but I would say new stuff every three years,
providing you keep the machines cool, clean, and turned on. Nothing seems to
hurt electronics more than heating and cooling cycles from turning them on
and off.

Look up the specs on the electrolytics used on the boards. Most have
a 2000 hour life rating at the specified temperature. After that, the
ESR starts to rise, causing the boards to fail.

BTW, my background is in mission critical electronics.

It also assumes a good power system to avoid low and spike voltage
conditions.

Around machine tools?-

Not quite what the Nichicon spec sheet here says:
http://products.nichicon.co.jp/en/pdf/XJA043/e-hm.pdf

After 2000 hours at the specified conditions, leakage and ripple are
still under initial specs.


That is all that most are warranted for, and rarely ar the run at
full temperature, so you extend the useful life. Motherboards use 105 C
rated electrolytics, but the boards are never run at that temperature,
the 85 degree rated electrolytics drop like flies.


That said, the cheap electrolytics on consumer motherboards are what
usually goes bad the quickest, given otherwise good power and
environmental conditions. I just had to pull one and stick in a
spare, it'd been in service pretty much continuously for 5-6 years.
The big caps all had bulgy ends. I'll try reviving it with some new
caps, they're cheap and it's a fairly quick fix, if it works.


Use a grounded vacuum desoldering iron to remove the bad caps, and
make sure to clean off any electrolyte that leaked. Inspect the traces
near the bad caps for erosion of the copper before soldering in the new
caps.


So for the O.P., I'd figure on a max lifetime of NEW boards at about 5
years. Used ones are a crapshoot. You might improve things with
better-quality caps, assuming you have the facilities and ability for
changing same.


If the motherboard was built with cheap electrolytics, you may not
get a year out of it. A lot of Chinese capacitors were made with a low
grade electrolyte that causes the foil to be destroyed. It wasn't much
better than the salt water used in early homemade electrolytic caps in
the early days of radio. There were dire warnings not to use any
electrolytics back then, because they would develop high leakage
currents and burn up the power transformer.


--
You can't have a sense of humor, if you have no sense!