PDP-8/L and TTY stuff (was Re: TTY and current loop questions)

From: Ethan Dicks <ethan_dicks_at_yahoo.com>
Date: Thu Dec 16 23:22:04 1999

--- Tony Duell <ard_at_p850ug1.demon.co.uk> wrote:
> > > Do you have the 3 grey books for the ASR33? Volume 1 of the maintenance
> > > manual covers lubrication.
> >
> > If I do, it's long buried.

BTW, are these 8.5"x11" paper or 11"x17" paper?

 What's the synopsis for the area around the

> Well, the general idea is to clean and dry the type cylinder and the
> hammer face...

One thing that I did mention and I'll mention again is that my hammer face
is not original - I stuck on a rubber sticky foot and I suspect that it is
part of the problem. I read here recently that someone has had luck with
carved pink pearl erasers, but I haven't tried that. Worst case is I can
nab the printing mechanism out of my wire-service TTY, the one with the 110
baud data set (modem) built into the pedestal. It doesn't fix this one, but
it does get me up and running more quickly.

The other thing that sticks is the line-feed mechanism. I can see the pawl
on the back side of the ratchet at the left of the main roller and it doesn't
always spring back up. Presumably it's another lube job waiting to happen.

Neither of these teletypes has been stripped down in the 13+ years that I've
owned them. To make matters worse, neither one has been powered on in ten
years. I haven't had time to work with my classic machines until this year.

> However, if it's actually sticking, then either something is bent or the
> old oil is gumming it up (probably the latter). In which case _I'd_
> dismantle the carriage totally, clean all the parts in a suitable
> solvent, put it together and oil it.

I can get for under $15 a disposable carburetor solvent bath-in-a-can at a
local auto parts store. Presumably, this is a suitable solvent. The print
mechanism should fit nicely for immersion.

> I did my first teletype without the manuals, but unless you had a
> misspent youth like me dismantling and reassmbling everything in sight,
> I'd not recomend it... With the manuals it's not too hard if you're
> generally OK with hand tools.

I used to disassemble sewing machines as a youth. I never tried putting them
back together, but I'm OK with hand tools. I just repaired the works of an
upright piano that I was gifted with - its problem was dried and cracked glue
joints on one key mechanism and the entire damping bar. Obviously, a teletype
has more moving parts than a piano, but there is a superficial resemblence.
> > How many types/grades of lubricants are there for a proper lube job on a
> TTY?
> 2 AFAIK. One is an oil. It's a light-ish (SAE 10 or thereabouts) engine
> oil. I normally use the lighter of the 2 oils recomended for my Myford
> lathe, as it's about right and I have an oilcan of it anyway. But any
> light machine oil (NOT WD40!!) is OK.

Sewing machine oil? "Three-in-one" brand general-purpose oil? Am I on the
right track here?

> The other is a grease. Just general-purpose high melting point grease,
> like you'd use on a car (Oooops, modern cars don't have grease points
> :-(). Castrol LM or something like that.

I also restore Volkswagens. I know what a grease fitting is and how to
operate a grease gun. (As an aside, I just got a 1975 Microbus in operating
shape for $300 - it needs some work in the fuel injection system, but otherwise
> If you can find the manuals, I can talk you through taking the carriage
> out and apart (the manaul is not that clear in places). Without them it's
> going to be more difficult, if only because of problems in refering to
> parts (with the parts list I can use Teletype part numbers).

Maybe someone will eventually scan a set it as was mentioned here.
Alternatively, there is always the route of borrowing, xoxing and returning
a set.

I was looking at things again tonight... the -8/L is not 100%. I had to remove
the PSU to fix the loose fuse holder - it wasn't just loose, the side lug had
a cold joint on it. I had to remove the mains-in and mains-out sockets to get
room for my tools, but all is well on that front now. The problem is that the
machine does not correctly run the RIM loader. If I put a halt (7402)
instruction in low core, location 0, say or even 20 and I run the RIM loader,
after reading in one character, the CPU halts at that low core instruction.
If I single step things, it does not wander off into low core. Another
wierd symptom is that pressing the START switch increments the PC address, but
only on the same page (i.e., 7777 becomes 7600)

OTOH, some programs do work. I wrote a quick-n-dirty echo test. It works
fine with my VT220...

0200 6032 KCC
0201 6031 KSF
0202 5201 JMP .-1
0203 6036 KRB
0204 6046 TLS
0205 6041 TSF
0206 5205 JMP .-1
0207 5200 JMP 0200

Nevertheless, the RIM loader fails if I put the CPU in RUN mode without the
single-step switch thrown. Back to the drawings. Sigh.

Thanks again for the good info.


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Received on Thu Dec 16 1999 - 23:22:04 GMT

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