22 Jan
2021
22 Jan
'21
7:18 p.m.
Moving parts are trouble, absolutely. That's why I built one of David Gesswein's
MFM emulators recently to replace the original hard drives in my Pro.
Then again, other parts can fail. The power inlet filter in my Pro failed spectacularly
(smoke, melting, stink). Fortunately replacing that is easier than replacing an ancient
hard drive. And that is a common point: many electronic things can be replaced by modern
parts, while mechanical things are far more problematic.
SSDs can fail, though, especially at modern densities. I recently saw a 256 GB microSD
card; that boggles the mind. I wonder what the life expectancy of one of those is. SD
cards certainly have write limits, so any that are written to a lot are likely to fail at
some point. More quickly if they are subjected to short (one block) random access writes
due to "write amplification".
Modern politically correct solder can be problematic too. "Lead free" processes
are less reliable than real soldering. For years, maybe still, lead free solder was not
acceptable for space applications. Perhaps that has been cured by now, I don't know
and don't care. (I was told quite directly by a professional "if you are
required to use lead free solder, do so. If you aren't required, avoid it.")
I do like SSDs. My home firewall, DECnet router, and Subversion server is a fanless (heat
sink cooled industrial type) SSD based PC running Linux. Unlike its plain consumer PC
predecessor, it has no objections at all to spending its life in a dusty basement.
paul
On Jan 22, 2021, at 12:03 PM, Johnny Billquist <bqt
at softjar.se> wrote:
Well, I know of PDP-11 systems out in production who have been running since the early
80s. The only thing that fails is the damn RD53...
Replaced those about 20 years ago now. The rest of the machine was running just fine. At
that at a steel mill, so not exactly a friendly environment. Last I heard, things were
still running, but it might have been replaced by now. But anyway, it's the moving
parts that cause problems. The rest usually just keep running...
Johnny
On 2021-01-22 17:53, Dave McGuire wrote:
On 1/22/21 11:41 AM, Thomas DeBellis wrote:
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol 10 years used to be nearly unheard of for retail
machines with moving parts. When nothing is moving, then supposedly there is nothing to
burn out.
I don't know who told you that, but he/she knows jack point squat
about electronics.
Materials migration and diffusion across junctions causes semiconductor components to
fail, tin whiskers cause shorts, some types of capacitors dry out and/or have their
electrolyte deteriorate or crystallize, resistors drift, heat/cool cycles cause PCB
flexure resulting in cracked solder joints, corrosion in air creeps into connector pin
interfaces and forces pins apart, the list goes on and on and on.
To be fair, some of the above-listed failure modes do in fact involve things moving,
though imperceptibly so, my point stands.
-Dave