Jon Elson wrote:

Michael A. Terrell wrote:

?
?
? Yet you can't repair it without buying modules from other people.
?
?
Before EMC (the original one) or Mach, I bought an Allen-Bradley
7320 control from a guy in California and got it running, with great
difficulty. It didn't come with the executive tape or servo amps,
which were supposed to be part of the package. I had to make my
own servo amps (this was before eBay, too), get an executive tape
from a guy who repaired these, and then patch the executive for the
encoder resolution I had. I built my own BTR also, using an old
laptop for storage of G-code.

I COULD repair it, and had to do so on a regular basis. This was
a 1978-vintage control, and I was trying to use it in 1996-1998.
So, it was roughly 20 years old at the time. EMC came along just
as I was getting seriously frustrated by unreliability of the thing.
There were some problems with the original EMC, and so I went back
and forth a couple of times (I had rigged some connectors so I
could switch between the two pretty quickly.) Well, after the 3rd
swap, EMC was good enough that I never powered the A-B control
on again.

Besides the reliability issue, EMC stored G-code on a computer
with a hard drive, you could edit the G-code on the EMC PC, the
PC was on the local network, You could run primitive diagnostics
on the machine, and the servo response was a lot "snappier".
I'm probably missing a bunch of other features.

A PDP-11 based control is probably a few years newer, but many of
those controls had a VERY limited user interface. Not too bad
for selecting a stock program and running it, but pretty
primitive for editing programs at the machine, for instance.

Oh, and finally, if you look at what the vultures charge for
a board out of a 30 year old control, you could replace the entire
electronics of a modern Pico Systems or Mesa interface from
computer through the servo amps for what one replacement
board would cost.


Jon, I have repaired electronics for over 45 years. That's how I
made my living, and a lot of that work was to repair digital circuits.
My computer work has ranged from the KIM and the 4004 processor, to
embedded controllers aboard the space station. I have a copy of 'Linux
CNC' and most of the parts on hand to build a mini mill but a machine
that size would get very little use in my shop. I should still have a
full set of the manuals from Heathkit for their LSI-11 based computer
which basically kitted the DEC system, under license. I have repaired a
lot of equipment without manuals. I have a dozen National Semiconductor
memory boards for that series that were pulled from working DEC systems.
I could probably design and build a replacement for any bad board for
less than the vultures want. Or just buy the non working stuff for
salvage from someone else guts when doing a conversion.


Most of the parts I would be making would be to repair existing
tools, or to prototype a design project. I am 100% disabled and no
longer have access to the machine shop where I worked, so I am trying to
piece together what I want, for whatever time I have left. It's the
only way I can work, given my health and my budget.


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