[GreenKeys] Seeking Teletype Part 1882241

[Eric Moore]

Thank you, this is very helpful.

-Eric


On Sat, Jun 5, 2021, 4:54 PM Jim Cooper <jim.w2jc at gmail.com> wrote:

> On 5 Jun 2021 at 15:23, Eric Moore wrote:
>
> > There appears to be a ground fault
> > with the teletype that is preventing
> > the system bus from being used when
> > the teletype itself is energized. It
> > is in fact setting a bit in one of
> > the computers registers. The
> > teletype itself can be bypassed
> > luckily with an adapter, which is
> > what I have been doing up until now.
>
> not sure what you mean by a 'ground fault' ...
> related to the AC power?
> related to the loop current?
>
> tread carefully in either case.
>
> > After basic maintenance I was hoping
> > to get to expected behavior when in
> > local, then was going to use an
> > RS232 adapter to test online mode
> > with the teletype off its pedestal,
> > and use that opportunity to try and
> > find the ground fault.
>
> get the monster to work properly
> OFF-line, on just a local DC loop --
> 60ma or 20ma, depending on how the
> selector magnets are wired.
>
> don't even mess with an 'adapter' or
> terminal unit until the printer works
> properly on the local loop, with the
> keyboard in series with the loop. You
> should be able to type on the keyboard
> and see exactly what you typed show up
> on the paper !
>
> > Is maintenance easier to perform
> > with the teletype removed from its
> > base?
>
> depends on whether you are talking about
> mechanical maintenance or electrical loop
> testing.   For mechanical work, yes -- off
> the base, you can still turn the shafts by
> hand and watch how everything responds.
>
> when you are happy with the mechanical
> machinations, then put it back on the base
> so the motor gear is engaged and you can
> turn the motor MANUALLY (without power)
> to be sure everything still follows along as
> it should.
>
> THEN connect up the dc loop and set the
> current correctly (60ma or 20ma, as noted
> above).  If you don't have a local loop (instead
> of an adapter or TU), MAKE ONE!!   not hard
> to do ...  60ma is not a lot of current or power,
> you could even use two 6.3v filament transformers
> back-to-back to get the isolated 120vDC !!
>
> YES, you want 120vDC ... important ... because
> with the high voltage, you need a high-ohm
> resistor (nominally 2000 ohms) and you need a
> high ohm resistor to assure good 'time constant'
> for the square wave signal.    The time constant
> is based on  L / R ...  inductance of the selector
> magnets divided by the Resistance in the loop ...
> big R, low time contant, squarer square waves !
>
> Once the mechanics are good and the typing unit
> is back on the base and turning the motor manually
> makes everything go smoothly, then you can connect
> the local loop and turn on the motor AC.  At that
> point, everything should be quiet and steady aside
> from the sound of the motor whirring.
>
> Press R on the keyboard - hopefully see R type on paper;
> Press Y on the keyboard - hopefully see Y type on paper.
>
> If both happens, you are probably successful.   :))
>
> (Note that R and Y have opposite Baudot code bits,
> that's why RYRYRYRYRY is used for testing 5-unit
> teleprinters -- it makes everything in the selection
> mechanics go from one extreme setting to the opposite).
>
> Hope that helps.
>
> w2jc
>
> btw: for those reading, I have a few more M-14/15/19
> AC synchronous motors if anyone is in need ... contact me.
>
>
>
>
>
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