While not on a 780 back plane, about 50 years ago, I was basically in
charge of some 26 PDP16M computers. Periodically, one of the chips would
be found with the top blown off. At some point, I pulled the computer
and examined the backplane filled with wirewrap wires.
The solution turned out to be fairly simple... a -15V bus was about
.001" near one of the wirewrap posts. A slight moving of that bus away
from the wirewrap post solved that problem. I have to assume it was a
temperature related problem since increasing that spacing solved the
problem.
Unrelated to the computer problem, another source of angst was
intermittently one of those computers would crash. That one took
probably a year to find... one of the interface M series pullup cards
had a pulldown card installed in its place.
I should mention all the above took place on a newly install system.
Marvin
I worked part time at a computer center for a large bank while getting my undergraduate degree.
The center was getting one of the first IBM 3081 machines to replace the existing 3033 MP.
Because of the helium filled modules, getting the machine from the climate controlled truck to the center, which was on the 7th floor of the bank building was crazy; the move had to be accomplished in 30 minutes. As a dry run, IBM supplied a size and weight dummy 3081 in advance to make sure the delivery went smoothly.
As you might imagine, the install and switch over to the 3081 was high profile. The VP in charge of the center was under pressure to get it done on schedule.
The delivery and initial install went according to plan. The data was migrated to the new disks and the various application software was run through its paces.
Unfortunately, the 3081 would occasionally throw a power fault. The local FE’s could not determine the cause, so after a week or so second level support was called in. They could not figure it out, so IBM brought in Ivan (I think that was his name). You know when you get the hot shot from IBM when he arrives in bib overalls and tennis shoes, not a suit and 5 pound wingtips.
After the second day, Ivan got tired of the stream of managers asking him when the 3081 would be available, so he went down the the main bank floor and grabbed the thing (I cannot remember the proper name) banks used to use to create teller lines (posts and satin “ropes”), and formed a cordoned area around the 3081’s console. Note that each computer console had a telephone (1 for each 3033 and one for the new 3081) for communicating with the computer operator.
On the third day, the VP bypassed the cordon and asked Ivan when the 3081 would be operational and Ivan replied he was’t sure. The VP said he had already told the president it would be up by the end of the day, and Ivan handed the VP the phone on the console and said, and I quote, “Call someone who cares”. I kid you not, I still remember verbatim.
Early afternoon of the third day, Ivan asked the Lead FE to get a torch. There was an awesome hardware store about 6 blocks away, so in about 20 minutes the torch was delivered.
The power bus on the 3081 had enormous cables composed stranded 4-6 large gauge wires that were soldered to large metal plates. Ivan had determined that the wires were improperly soldered and used the torch to resolder them.
You can imagine the horror on the faces of the staff as Ivan opened the power bay, lit the torch, and started melting the solder.
And it worked! No more power faults.
— Todd
As requested, here is a partial list of the 8-A parts available. I have a
few more to go through, but most are on here except for possibly a 128K
memory board.
I have some omnibus boards, M8357 RX8e, LA180, LQP, etc, and will try to
make a list next week. If you need something not on here, please ask.
I have at least one of each of the following, and more than one of some.
G8016
G8018
H9194 12 slot 8-A backplane
limited front panel
programmers panel
MM8-AA
MM8-AB
M8315
M8316
M8317
M8319
M8416
M8417
Also some non dec:
REMEX PC8E
core memory
A complete 8-A mounted in the desk with RX02s. It's currently in the back
of a 20 or 25 foot rental locker, but I hope to get it out this summer. It
came with a LA35 and maybe a VT52.
Dear list members,
I was wondering if anybody is aware of VAX 86x0 schematics having survived the product life cycle within DEC? I searched the web extensively but could not find any hints on this.
It seems that DEC never published such details as schematics for the successor of the VAX 11/78x systems, not even on microfiche, maybe due to the macrocell array implementation (just a guess). All I could find is that there were illustrated parts list on microfiche.
However, maybe Hewlett Packard handed DEC-internal documents over to a museum such as the CHM? Or a former designer still have schematics in their archives?
Any pointers would be greatly appreciated!
Best regards,
Pierre
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http://www.digitalheritage.de
Jon Elson's take hits home. A 780 was delivered and VMS was running. We
installed 4.1BSD and it ran fine until it crashed. Field service insisted
we needed a full set of RS-232 wires in our cable. Still crashed
(surprise!). Switched to VMS, still crashed after a while. Local field
service couldn't find it. The big guns flew in from Maynard. First day:
Couldn't find it. Second day: "What, what's that wire doing there? Have a
wire-wrap tool?". Removed wire from backplane. Boots, runs. Engineer
flies home.
Side tracking slightly from the "VAX 86x0 schematics" discussion into changing field service procedures over the years: I remember some fairly hairy cases in the 1970, when FS engineers had to be way more capable than board swappers.
1. DEC RS64 fixed head disk was behaving badly, making more noise than expected. Machine was not under contract. FS tech took it apart, diagnosed bad bearing. To save the customer (college physics department) a pile of money, he took it to Appleton Electric Motor Co., where they found a suitable bearing, pulled off the bad one, pressed a replacement on. Jim reinstalled the motor into the drive, worked great.
2. Same college, different machine: RF11 drive was showing "clock track failure". Diagnosis: drive is not spinning. Same tech. Jim took the drive apart on a desk in the computer center, noticed a head had crashed and melted, hot-glueing itself to the platter so the motor was blocked. This machine was under warranty, so he ordered a pile of parts: full set of heads, motor, platter, plus tools. Replaced the motor, replaced all the heads and aligned them, replaced the platter, and formatted the timing track. The manual for that formatter was not exactly intellegible...
3. Different university, CDC 6500 mainframe, occasional data corruption in one of the mass memory transfer paths. After lots of test code added to the application (PLATO system), the tech concluded he knew the answer. Opened up one of the cabinets, lifted up a massive bundle of wire to reach a spot where one of those wires was "punched in" to a module connector, and re-punched the pins of that wire. Repeat at the other end of that wire. Run tests, problem fixed.
In that machine, there were a dozen or so chassis, with up to 750 or so modules, each with 28 signal pins, most of them interconnected to elsewhere with twisted pair wires terminated in tapered pins that were pressed into place. It was a surprisingly reliable system but we learned it wasn't 100%, and it took quite some skill and perseverance to find which of those tens of thousands of wire connections was the failed one.
paul
Hi Paul
I see that you are clearing out QBUS board. I've been looking for a
"DIGITAL Q BUS music board" for a while. It is a board without M-number
as it was never sold. It is a simple dual board with two AY-3-8192 chips
on. There are pictures available, if you want I can send them to you.
I live in Sweden, I hope we can work out shipping if you have the board.
Regards,
Pontus.
I was digging through DEC compatible boards for someone and realized I
should have posted them.
I have over 100 dual, quad, hex and VAX boards from the usual suspects-
ABLE, CMD, DIGITAL PATHWAYS, DILOG, EMULEX, MT, PLESSEY, REMEX (paper tape
interfaces for 8s and 11s).
Included are core memory boards for 8s and 11s.
A small data book library at my work is going to be cleaned out soon. It is
mostly common stuff from 1995 and older. I don't believe there is anything
unique.
You can see a some pictures of the shelves here:
https://photos.app.goo.gl/jdJnUdRPvzvRzeTp6
I can't sell them and I won't ship them.
If you see anything that should be saved I will squirrel it away with the
intention of scanning and getting it online someday.
-chuck
