seeking info on ASR-33 interface board

From: Tony Duell <>
Date: Wed Aug 4 18:13:14 2004

> Hi Y'all,
> I just popped open an ASR-33 I picked up a few weeks ago. The tty ran
> OK in local mode in the store where I found it but in shipment to me
> something happened, it now free runs (runs free?). Maybe it's a loose
> connector.

Did you fit the transist screw underneath to clamp the 'typing unit' to
the base pan? If not, then I'll bet the typing unit has jumped off its
rubber mountings. If you're lucky, all this will have done is caused the
kyboard linkage to get stuck in the key-pressed state, and refitting the
typing unit properly will get the machine back to rights. If you're
unlucky, you'll have mangled some of the linkages in this area (front
right of the typing unit, and the same area of the keyboard) and you'll
have some sorting out to do.

> In the electronics bay on the right hand side, there's a printed
> circuit board that runs from front to back. It's definitely a power
> supply, and probably also an RS-232 to current loop converter. In

The basic typing unit has a bare solenoid for the RX input. The Teletpye
priveate line call control unitinterfaces this to a 20mA or 60mA loop.
Your board _might_ be an RS232 converter, it might be a current loop
converter, it might be almost anything. I cna't believe it's that
complicated, so you could trace out schematics.

> Was it common to produce custom internals like this for teletypes?

Not that common, but not unheard-of either. One of my ASR33s has Data
Dynamics electronics (and a Data Dynamics all-metal cabinet, with light
bulbs to illumnate the printed paper, etc) which provides both current
loop and RS232 interfaces (with the right cable).

Of course many companies fitted reader-control relays (DEC, Intel, HP,
etc), but generally those were an add-on to the Teletype private line
call control unit.

Received on Wed Aug 04 2004 - 18:13:14 BST

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