[GreenKeys] M28 printer troubleshooting - type box positioning

[John Doe]

Good update!

That missing spring would certainly cause problems.  If you need help
taking the front off the printer to access the spring, let me know.  I've
done it about 7 times and it's not difficult.

Keep up the good work,

Nicholas Gromak.

On Tue, Oct 14, 2025 at 6:24 AM Dale Hughes <dalevk1dsh at gmail.com> wrote:

> Hi Nicolas,
>
> Many thanks for your thoughtful reply and I have checked those parts of
> the machine, all the springs are in place. I have checked the operation of
> the selector mechanism a number of times and it seems fine. Sending the
> various bits, either as a single bit, or combinations of bits,
> generates the correct mark-space positioning of the code bars. I was
> puzzled for a while about the common bar, but it became clear that there
> are in fact two 'common' arrangements. The first one is bits-1 and 2 which
> is the common code bar that comes from the selector mechanism and this is
> used for the vertical positioning of the type box. There is also another
> 'common' for bits-4 and 5 which are part of the horizontal positioning of
> the type box. Bit-3 selects which side of the neutral alley is used as
> you have pointed out.
>
> In the meantime I have found there is a spring missing on the bell crank
> that links the code bar for bit-4 to part of the horizontal
> shift mechanism. It seems that the missing spring causes the
> horizontal shift to miss a column of characters depending upon the
> direction of travel which is what I was finding when sending the character
> pairs. In that part of the machine there are three small springs which
> restore the 'plates' (I'm not sure what else to call them...) for bit-4,
> bit-5 and the combined bit-4-5 combinations which determines which column
> of characters in the type box is used. Bit-3 selects which side of the
> neutral alley is used as you have pointed out. It's a very clever system
> for sure. Nick England sent me a link to a useful document (you may have
> already seen it):
>
>
> https://www.navy-radio.com/manuals/tty/jh/ttyman3/TeletypeManuals/model28/Instructional/28_Printer.pdf
>
> and pages 21 and 22 show the relevant functions for the type box
> positioning which helped me to locate where the spring is missing. It's a
> tiny little spring and I hope I can get some to replace the set of three...
> They are Teletype part number 45027 which I found from the assembly
> diagrams in one of the Teletype manuals. Of course there may still be other
> problems once the springs are replaced and I'll have to deal with that
> situation if it arises...
>
> I hope your restoration work is going well! Thanks again for your
> suggestions.
>
> Regards
>
> Dale
>
>
>
> On Tue, 14 Oct 2025 at 02:07, John Doe <jdoe10449 at gmail.com> wrote:
>
>> Hi Dale, how ya goin'?  Greetings from Canada.
>>
>> I'm new to the group too and I've been restoring an M28 ASR for the last
>> 6 months or so. The mechanism is still fresh in my mind and I'd like to
>> take a crack at helping you with your machine.
>>
>> Good work testing and gathering the data to share. I can't claim to be an
>> expert but something didn't sit right with me in your message. Your quote
>> here:
>>
>> *"The problem seems to be with bit 4 going from mark to space if bit 5 is mark. There is no problem with bit 4 = space (...) The state of bits 1,2 and 3 don't seem to matter."*
>>
>>
>> It's my understanding that the only difference between H-T, Y-Z, P-L,
>> Q-W, is Bit-3. Please see the attached "Dales_Machine_1.PNG" for a map.
>> Both columns are fixed by bits 4 & 5 - the left column (HYPQ) if bit 3 is
>> on or the right (TZLW) if bit 3 is off - and the rows are selected by the 4
>> possible combinations of bits 1 & 2.
>>
>> If you and the others in the group can agree that Bit-3 is the problem,
>> let's start with checking the selector mechanism (I know you checked it
>> already). See attached "Dales_Machine_2.PNG". Let's hope it's just a lack
>> of lubrication or a missing spring. Repeated information: Check that all
>> springs are present on the push levers and intermediate arms and verify
>> that movement of the mechanism is snappy and free of sticking.
>>
>> Amendment: You may need to check the springs on the selecting levers that
>> ride the cam.  I failed to highlight them in the attachment because you
>> will probably need to remove the typing unit to be able to see them;
>> they're underneath.  It's not a difficult job - just 4 screws to remove and
>> the typing unit should pull straight up.  Get a sharp 10" long flat head
>> screwdriver - preferably hollow ground and press down hard on the selector
>> side to prevent the driver from slipping.
>>
>> Hope this helps.
>>
>> Nicholas Gromak
>>
>>
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