Teletype: well one is still in my car, minus its stand and
plastics, and the other is in the house. I bought a new typewheel and
hammer from Wayne @
teletypeparts@aol.com,
but I haven't worked on the power supply for it yet because the 8/M's
supply arrived back from England with a clean bill of health, so I sunk
my teeth into that project instead, and now the teletype is 2m off the
ground on top of my bookshelf and I ABSOLUTELY CANNOT BE ARSED getting
it down. No, like, just no desire whatsoever at the moment. It can stay
there and hold the bookshelf down. Meh.
PDP: So anyway
I brought the 8/M up, and it
(unsurprisingly) stuck its tongue out at me. It's not the PSU, since
that's now totally rebuilt and absolutely with like-new functionality;
or the CPU or core, since I tried combinations of all that I have and
the symptom is completely unchanged. It's somewhat random but the most
common fault is as follows: one bit is stuck on, and if you hit DEP it
goes into RUN and stays there. So I'm pointing the ol' Finger of Blame
at either the backplane (things change slightly - never actually
working, but sometimes there's no stuck bit - as I move the boards
forward and back in there, weird no?) or some component on the front
panel, since those are the only other common bits. I'd love to add the
8/E into the equation but its PSU is very insistent about eating one of
its capacitors and TBH I just need to hunt down some place in NL/BE/DE
where I can *have* it repaired. Actually it might be an idea to solder
up the blue wire for the 8/M's unspecified whatsit connection to the
8/E's backplane, as they're otherwise the same, and that would let me
rule in/out the backplane as the cause of my woes.
Anyway. The 8/M. I
checked the diodes. I checked the capacitors as well as I could without
a capacitance tester (€700 for a new Fluke is out of my budget
presently). Resistors are a pain to test in circuit but I did my best,
-ish. That leaves the ICs.
So, naturally, I sat down with my TTL
tester and oscilloscope and probes and and my variable power supply and
little clippy-on power leads with the banana plug on the other end and
had a sudden realisation, nay call it an
epiphany even....
...that
I have
absolutely no !@#$% idea how to troubleshoot the things.
Oh yeah, I meant to look into that. Analog != digital. 555 timer != *.
Details...
Fast-forward a few days, I've got my book on TTL
basics from Amazon, dragged out my old breadboards and bags of random
sweepings/components from Maplin's back in Dublin, and my genuine 1989
Radio Shack 60/40 lead solder *which I spent a fiver on by myself back
in 1989 I would like to add, very proud I was of my big roll of solder,
now I could build stuff just like my dad,* discovered that I actually
have a few 7406 (yay NOT gates) and 74LS86 (yay XOR gates) from
gods-know-what random project I was apparently working on, obviously
from schematics, etc. And now I am (with a slight interruption due to
the acquisition of a
kittycat on Sunday) setting into
actually figuring out how to test this stuff. Wish me luck?
But I
really wish I had one of those other more experienced vintage computing
people around to offer me assistance because I am flailing in the dark
here. Are you such a person? Do you know something I don't?
Please contact me!
(By the way, this colour scheme is a default
Google Sites choice. It's not quite PDP-8, but pretty damn close!)
