[GreenKeys] 28 ASR/Dometop - Why does the motor pinion gear break?

[Nick England]

The capacitor in the base of the motor unit is necessary to start the motor
turning in the proper direction. If it is bad the motor shaft will just sit
there quivering.

Yes the motor gets hot during normal operation- there’s a warning label on
some.

Does your ASR have a perf or reperf connected to the keyboard? The dome
(auxiliary) reperf is mechanically separate from the rest of the ASR and
has its own motor.

Sounds like you have something binding.
Turn power off. You should be able to turn the motor (top of fan end toward
you) fairly easily, causing the printer to cycle open with the hammer
striking a blank.

But I would start by removing the typing unit so that the motor is only
driving the TD and the keyboard perf/reperf. Then the motor should be
really easy to turn.

Do not ever rotate the motor the wrong way - the typing perf/reperf will
jam and can only be fixed by some long-retired ladies at the Teletype
plant.

If things are binding with the typing unit removed, you can loosen and
slide the shaft couplings to the TD and perf/reperf in order to isolate the
problem.

My $.02 worth.
Nick England K4NYW
www.navy-radio.com


On Mon, Jun 9, 2025 at 6:38 PM Jeff G <jeffg at junknet.net> wrote:

> So let's start some discussion and things to look at - Why does the motor
> pinion gear on our 28 Dometop (tty #2) at the ship keep breaking, and how
> can I "test" for it? I need to solve this for sure before putting any more
> 45 baud gears into it, and for now, I'll prob put the 75 baud set back in
> temporarily.
>
> Originally I suspected the intermediate gears were never aligned/adjusted,
> but in swapping the latest gear set, I made sure the gears were meshed well
> but not tight. I also took that assembly apart and re-greased the bearings
> on it with mobile-1 grease. The printer was printing great, in fact,
> SOMEHOW, it was still going despite half the pinion gear being completely
> missing! (The intermediate gear survived undamaged as well).
>
> In both cases, the unit was on/running for a while (first was sitting
> idle, this time it was printing) and in both cases, I came back to it
> making noises after the gear went.
>
> Now, I'm suspecting either the printer or perhaps the TD is adding more
> drag than normal, causing both the gear to be under load, and in the case
> of the TD, the drag causing the motor to get hotter than normal. In this
> case, would it be normal to check the amount of current the motor is
> pulling? Next time I go in (which may not be for a couple weeks), I'm also
> taking a laser temp gun to take a reading off the motor with just the TD on
> it. There is a capacitor on the LEU? that I'm not sure is part of the motor
> or not (I think I'm gonna say no). Also the electrical filter at the bottom
> was bypassed as that blew up too. (This unit is definitely giving me a
> college course on TTY).
>
> The next thing is - I was originally running the printer with no screws in
> the print mechanism (but solidly seated). Both cases it wasn't until after
> I screwed down the printer with a couple screws on opposite corners did the
> gear break, so I'm wondering how the printer gets adjusted to the
> intermediate gear, since there's no way for me to adjust that with the
> printer in place. (I think)
>
> Without going through the 1900 page manuals, are there any temperature
> specs for the motors?
>
> Any other ideas? You guys are the experts! :-)
>
> Jeff
>
>
>
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