ASR-33 Restoration

[Tony Duell]

> Does anyone have any pointers or good reference sites on testing and 
> bringing one of these things back to life?  I want to start at ground 
> zero.  One of the TTYs seems to power up fine and the motors run, but I 
> can't get the keyboard to type in local mode.  The keys don't press down 
> all the way.  The shipping bolt was not in place when these were 
> shipped, and I know they were picked up and tilted and moved around, so 
> things inside may be out of alignment. 

The big problem with shipping Model 32 and 33 Teletypes (and this will 
hopefully help with Sellam's question a few messages later one) is that 
the typing unit -- the diecast frame with the motor, platten, all the 
printing mechanism and even the punch -- is not fixed down. It rests on 4 
rubber mounts in the base pan.

The only mechanical linkage to the rest of the machine is the infamous 
H-plate. This is at the rear right of the keyboard and connects a linkage 
on the keyboard to a linkage on the typing unit. When you press a key, 
the linkage on the keyboard rotates (front edge moves up IIRC). This 
twists the H-plate, opertating the linkage on the typing unit. This then 
releases a clutch at the rear left of the typing unit, causing the 
transmitter shaft to spin and to serialise the character from the 
keyboard (that's what the distributor disk is for). At the end of that 
cycle, the same link on the typing unit is forced back again by a cam on 
the transmitter shaft. That forces the keyboard linkage down (it 
latches), reseting the keyboard.

There is one other sort-of link. A white plastic tab at the same corner 
of the typing unit fits under the stem of the run-out key. Pressing that 
key operates the linkage, causing the machine to transmit repeated NULs.

There is a hole in the base pan under the typing unit, which lines up 
with a hole in the typing unit chassis. You should insert a self-tapping 
screw there to lock the typing unit in place for shipping. If you can't. 
I'd remove the typing unit and pack it sperately. Removing the H-plate 
would help a bit, but if the typing unit breaks free, it will damage the 
plastic run-out linkage.

OK, in this case, I'd start by making sure the typing unit is correctly 
seated. If necessary remove it -- remove the H-plate first, unplug the 
wiring, and lift the typing unit up at the rear first and slide it out. 
You can then see how it should seat and refit it correctly.

The linkage the couples to the H-plate on typing unit is spring-loaded, 
and the H-plate has a deep notch on that side to clear the pivot pin. You 
can use a screwdriver in the obvious slot in the H-plate to force it to 
the left and then unhook it from the keyboard linkage. Then remove it 
altogehter. Refitting it is a bit of a fiddle, but it gets easier with a 
bit of practice...

-tony