22 Jan
2021
22 Jan
'21
6:39 p.m.
And speaking of power - the one thing that I have experienced a lot on
11/70 machines are the H7440 regulators. They tend to blow up. And
especially if just kept in storage for longer periods, and then starting
to be used again...
Don't leave these machines off. That's all I say. That's when you get
trouble.
Johnny
On 2021-01-22 18:36, Johnny Billquist wrote:
Not really trying to claim there is anything
particular about DEC
equipment here. While they were built properly, I don't think there
necessarily is anything exceptional about them.
But no, I do not believe any components have been replaced. One of the
biggest issue is when equipment are left turned off for longer times.
That usually seems to be the time when problems appear. These machines
are (or were) running 24/7, and have always done so. There might have
been one or another card replaced from time to time, since they were on
service contracts for a long time. But just by looking into them, if
something had been replaced, it was a long time ago. Based just on the
general look of the cards.
By the way, we're talking 11/23 machines here. So BA23 box. Not that
much loaded in them, so no big strain on the power supply.
My experience with 11/70 machines are the same. If they are kept
running, they usually just continue to work. If you have them off for a
couple of years, you'll have a lot of work before they are stable again.
But disk drives get into trouble with age, even if continually running.
And some are worse than others. The RD53 is sortof infamous here...
? Johnny
On 2021-01-22 18:15, Dave McGuire 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
?? Sigh, yes, we all know of exceptions.? But even then, I doubt it
can be proven that those PDP-11 systems in production since the early
80s have never had components replaced.
?? Not everything is built to DEC standards.? That said, all my life
I've been replacing chips, diodes, transistors, capacitors, and
sometimes even resistors in DEC gear.? It does happen, and it's not
uncommon.
?? The regulator bricks in the H742/H7420 power supplies tend to blow
Zener diodes.? That's fresh in my mind because we just lost another
one at the museum recently.? Those are failing with such frequency now
that I've purchased stocks of the components that tend to fail. (we
have a lot of those at the museum)? And those ARE built to DEC standards.
?? Speaking of not being built to DEC standards, I've got a Heathkit
H8 on the bench right now, I'm repairing it for a new exhibit at the
museum.? Four failed (non-moving!) ICs replaced so far, it's very
nearly done.
???????????? -Dave
On 1/22/21 12:03 PM, Johnny Billquist 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:
> 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