Trouble with ASR33

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Sun Mar 16 13:31:00 2003

> I'm currently fighting with an ASR33 trying to make it perform a carriage
> return. Currently, the carriage is stuck all the way on the right side
> and refuses to budge. I tried to find something inside that would release
> it but I haven't located the magic tab.
>
> I've noticed something else. When I have the punch turned on, the '8' bit
> doesn't punch. For instance, if I hit "RETURN" I get the 1 + 4 + 128 bits
> punched, but no 8 (1 + 4 + 8 = 13).

The 2 problems could be related. The 'block level description' of the
machine is :

Incoming data goes to the solenoid on the RX mechanism (rear left of the
'typing unit' (main chassis)).

The RX mechanism samples the position of the solenoid armature (there's a
camshaft in the middle of said unit), and thus converts the data to parallel.

The parallel data goes onto the rails that run across the machine under
the carriage (one rail for each bit).

3 mechanisms use these rails :
 a) The carriage, which decodes printing characters and prints them
 b) The punch, mechanically coupled to the left end of the rails
 c) The function unit ('Stunt box') which decodes control characters and
    performs the appropriate function.

So if the return character is not getting to the rails correctly then
firstly it won't punch properly and secondly, it won't be detected by the
approipriate lever in the function unit.

So let's get that missing bit back first. Are you running the machine in
LOCAL mode (i.e. from its own keyboard to the printer?). If so, the
problem could be in the transmitter side (contacts on the keyboard, for
example). Or it could be a problem in the RX unit (sticking lever). I
think it's safe to assume that the solenoid driver is not the problem
here (it's not going to mangle only one bit).

Incidentally, the carriage is fed by the 'spacing mechanism' which drives
the left hand sprocket for the toothed belt. At the bottom of this
sprocket shaft, right against the casing, is the spacing ratchet with the
pawls to move it on one character, and to allow it to be released for a
carriage return. IIRC, _carefully_ frobbing levers in this area will
release the pawls and allow the carriage to return.

> Whoever designed the ASR33 must have sold their soul to the devil to make
> it all work. It's amazing how intricate and delicate everything is, and
> how damn kludgy as well.

I find them rather beautiful...

-tony
Received on Sun Mar 16 2003 - 13:31:00 GMT