Reviving and connecting an ASR33

From: Ian Primus <>
Date: Mon Sep 22 19:23:04 2003

>> The paper tape reader doesn't seem to work. There is also a good
>> chance
>> that I don't know how to operate the paper tape reader... I punched a
> Do you have the reader PSU connected? This is a PCB in a metal box that
> was often fitted in the stand. Sometimes it was fitted inside the
> machine, on top of the 'call control unit' at the right hand side. But
> if
> your machine was removed from a stand, it's possible the reader PSU is
> missing.

It looks like the reader PSU is there, I followed the wires from the
reader unit, and they branch off into two smaller bundles at the back
of the power supply, one which goes to a large molex connector on the
back of the power supply/CCU, and one that leads near the front of the
machine, to a metal plate with a board on it, that contains a couple
large capacitors, a relay, a fuse, etc,. This plate is mounted behind
the knob on the front, and bears the warning "Warning: High Voltage",
so I am assuming that this is a power supply. Also, I would assume that
this is taking up what space would otherwise have been used by an
acoustic coupler or modem or similar device.

>> strip of paper with a string of text, then put it into the reader, and
>> threw the switch next to the reader into the "Start" position. The
>> teletype makes a lot of rattleing, but the tape doesn't run through
>> the
>> reader, and nothing prints.
> OK, sounds as though the transmitter clutch is releasing, as it should
> do. THen the contacts on top of the transmitter shaft (rear right
> corner
> of the 'typing unit', normally with white and black wires) should close
> for every revoulution of the camshaft to energise the reader solenoid.
> You might want to check these contacts (warning -- this is _NOT_
> isolated
> from the mains!)

Everything appears fine back there, the little arm is hitting a leaf
switch with a cover that says "Caution High Voltage". and it looks like
it's making good contact. I haven't tested it with a multimeter though,
right now I'm betting that the reader is waiting to be activated by the

>> The cover is cracked, but that isn't really a big deal. I should be
>> able to glue it back together. What type of glue is recommended for
>> teletype plastic? Just regular wacky glue, or some sort of epoxy?
> Get some 'plasic weld' or whatever it's called over there. It's
> basically
> dichloromethane (methylene chloride), and is a solvent for the plastic.
> Put the broken bits together and run a brush dipped in said solvent
> along
> the crack. It'll disolve the plasic and fuse it together. if you want
> to
> make a really strong repair, get a piece of fabric (I am not sure what
> I
> used, ask your wife/girlfried/SO for an offcut of shirt, or something
> :-)) and put it on the back of the join. Then brush more solvent onto
> that and force it into the plastic.

I haven't gotten around to tracking down any chemicals or glue yet, the
cover is a minor priority, my main concern is getting it talking to
something <grin>. That sounds like a good idea, I'll have to see if I
can find some methylene chloride. What sort of plastic are teletype
cases made of? I always assumed it would be a hard, brittle plastic
like bakelite, but it is more resilient and lighter than that. I don't
think it's ABS, maybe it's PVC?

>> The paper tape punch has quite a buildup of chad above the punch. It
>> doesn't seem to be going down into the black tube at all. Is this
> This is pretty normnal. In the end you get enough up there for the top
> bits to fall off and go down the tube.

OK, that makes sense. I think I need to clean the tube out though, I
just noticed a gunky glob of oily sticky chad at the end of the tube,
where it should dump into the chad box.
>> normal? Also, what can I do about the chad, since I don't have the
>> stand. I have the chad box, but I can't really attach it without the
>> stand. I'll probably end up building something for it, or maybe
> Run it with the punch overhanging the desk and arrange some kind of box
> under it. That's what I did with my first ASR33

Good idea. I can't believe I didn't think of that...

>> single sheets of computer paper in, but I should just be able to
>> remove
>> the tractor holes from fanfold computer paper and run that through,
>> right?
> It should print on just about anything....

Hmm, maybe I should try using that roll towel they have in at work.
It's more like writing paper than paper towel anyway, and I have used
it to write down wire foot markings and stuff while running cable
plenty of times. (there is never scrap paper around when you need it)

As for paper tape, I should probably order some of the proper oiled
tape, but will using unoiled tape damage the punch? Right now, I have
been punching a couple strips of regular computer paper, trimmed down
to an inch wide. Will this hurt the mechanism, or is it safe to use
plain unoiled paper. I have access to equipment that can easily cut
junk fanfold paper into one inch strips, and it can also cut a roll of
adding machine tape down to size as well. This would be cheap and fast,
but I wouldn't want to damage my machine to save a few bucks on paper

>> Where should I oil the mechanism? Right now, everything looks OK, but
>> I
>> should probably lubricate it someplace periodically, right? Similarly,
>> what sort of oil should I use? Just regular household oil, or
>> something
>> lighter/heavier? Obviously not WD-40, however...
> Get the ASR33 maintenace manuals (I think Al Kossow has them on-line).
> About half of one volume covers lubrication. For 'oil' use something
> like
> 3-in-1 or other light machine oil. For 'grease' use a normal high
> melting
> point grease like you use for general greasing on the car.

I'll have to hunt for those on the 'net, the manual would be very

>> And, of course, the inevitable question, how do I connect it to
>> something? It has a cable fitted to it which I understand should be a
>> current loop interface. It is a funny little six pin rectangular
> Yes, either a 20mA or 60mA loop (this is selecatable in the call
> control
> unit). Again you want the manuals. The pinout of any external connector
> is _not_ standard, but the wiring to the barrier strip on the back of
> the
> call control unit is. That will be a big help.
> Hang on, _6_ wires? That could mean you have remote reader control
> (many
> computer-interfaced teletypes had this), which could explain the reader
> problems. Every manufacturer did this his own way, but they were
> actually
> all fairly similar, so if you get the docs for one (the DEC one is
> probably the easiest to find), it will help in figuring out any mods
> you
> have.

This teletype isn't a _true_ ASR-33. It is actually a rebadged ASR-33
called a General Electric Datanet 730. I kinda forgot about that
earlier, I have been working with the cover off, and I always just
think of it as an ASR-33. That, and all the internal parts say
TeleType. I would assume that it is meant for computer control, and it
appears to have the reader power supply mounted internally. If it is
that the other two wires are meant to control the reader, what do I
need to do to activate the reader. Since this will be connected to a PC
running Linux initially, I don't think that there will be a convenient
way to control the reader from the computer. Is there a way of just
rigging up a switch, or temporarily disabling remote reader control?
One of these days, I hope to get a computer that can talk to the
teletype properly, but for the time being, it will have to be used with
either a Linux based PC or eventually on my Prime 5340 once I get an OS
to load on the Prime (another ongoing project...)

>> connector. I have found information on how to connect current loop to
>> RS-232, but what pin does what? Was there a standard? I would very
>> much
>> like to be able to plug the teletype into a UNIX box or something, or
>> maybe the Prime, but for any of those, I would need RS-232. Also,
>> since
>> the teletype can only print upper case, how does it render incoming
>> text? Does it just ignore all lowercase characters, or does it print
>> them uppercase? Does it send all uppercase or all lowercase? I have a
> It prints lowercase characters as uppercase (basically, it ignores bit
> 5
> for letters IIRC). It sends all characters as upper case from the
> keyboard.
> The punch and reasder correctly handle all 8 bits, though, so you can
> copy a tape with upper and lower case characters (or, indeed a binary
> program tape) without problems.

Hmm, if it sends all characters as uppercase, I will need some way to
change the PC to recognize that and convert it all back to lowercase or
something, since all of the UNIX commands are lower case. I assume
there is probably a setting in Linux somewhere to do that. At least
it's ASCII and not Baudot. That would be lots of fun...

Ian Primus
Received on Mon Sep 22 2003 - 19:23:04 BST

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