[GreenKeys] Model 14 keyboard adjustment

Sun Aug 6 13:33:19 EDT 2023

I went at it again and am now getting a lovely waveform. I did use some
3000 grit sandpaper, but very lightly just to break up the surface a bit
with a generous application of contact cleaner

I dialed in the timing, and got a perfect R on the decoder in loopback! I
am also getting lots of extraneous characters, so going to disable loopback
while I work on the printer, but still, progress.

Next, my vertical drive for the printer is not moving the full cycle
vertically, again. It is a symptom of a bad bend around the code arms this
printer suffered, and mis-alignment on the vertical printer cam arm.

I am afraid I may need to disassemble for the umpteenth time to adjust the
printer, again, again, again...

-Eric

On Sun, Aug 6, 2023, 9:47 AM Mike Douglas <deramp5113 at yahoo.com> wrote:

> Note that the loop adapter Eric is using has separate printer and keyboard
> loops and Eric has those loops wired separately on his Model 14.
>
> The printer loop has flyback capture onto a storage cap, along with a
> switching voltage boost option to generate the high voltage and quick
> switching times required by the high inductance selector magnet loops of
> the Model 14 and 15 era machines.
>
> The keyboard loop on this era of machine has to simply sense switch
> closures. Over a short loop (like we have in our labs), and given contacts
> in good condition, 15v is plenty to reliably test closure of the keyboard
> distributor contacts. A higher voltage does not “clean” the contacts, but
> instead, results in an arc that can briefly conduct through a layer of
> oxidation or oil film. The conduction, however, might be only for the
> instant of the arc (as you see in Eric’s video). In this case, the bit is
> still sensed incorrectly. The arc can also clear enough oxidation or oil
> away that then that spot continues to make low resistance contact while
> mechanically closed. In this case, the bit is sensed correctly. The problem
> with “cleaning” with high voltage is that each arc creates more damage to
> the contact surface and also creates its own burn residue that, in turn,
> raises contact resistance.
>
> I’d continue to work on the contacts with paper tape or a business card
> whetted in contact cleaner. Move the paper back and forth while you apply a
> bit of pressure to close the contacts against the paper and each other. The
> keyboard contacts on my Model 15 took quite a bit of work, but I was
> eventually able to get them under 1 ohm.
>
> On a “modern” model 33, the distributor is a carbon wiper with at least 40
> ohms of resistance, and even there, just 12 volts in keyboard loop current
> is reliable for reading the keyboard electronically.
>
> Mike
>
> On Aug 6, 2023, at 8:44 AM, Eric Moore <mooreericnyc at gmail.com> wrote:
>
> 
> Thanks all, makes sense. I am using deramps adapters, and I am fairly
> certain that if I can remove the deep layer of gunk/oxides/whatever that
> formed over many decades of shed storage on these contacts that were open,
> it will work great on the low voltage circuit.
>
> I say that because the start bit contact works beautifully. It is the
> other 5 contacts that were left open to the air (were mechanically open
> when stored badly) that I am having trouble with.
>
> I bet a good shot of high voltage would help, I have a high voltage supply
> out in the shed I may bring in. I expected the contact cleaner to
> chemically remove the problematic materials when combined with my
> mechanical cleaning, but apparently not.
>
> -Eric
>
>
>
>
> On Sun, Aug 6, 2023 at 8:33 AM Paul Heller <paul0926 at comcast.net> wrote:
>
>> It was around 2009:
>>
>> [GreenKeys] why high loop voltage
>> <http://mailman.qth.net/pipermail/greenkeys/2009-January/013324.html>
>> mailman.qth.net
>> <http://mailman.qth.net/pipermail/greenkeys/2009-January/013324.html>
>> <favicon.ico>
>> <http://mailman.qth.net/pipermail/greenkeys/2009-January/013324.html>
>> <http://mailman.qth.net/pipermail/greenkeys/2009-January/013324.html>
>>
>>
>> Paul
>> W2TTY
>>
>> ITTY: HTTP://INTERNET-TTY.NET:8000/ITTY
>> <HTTP://internet-tty.net:8000/ITTY>
>> ITTY 100:  HTTP://INTERNET-TTY.NET:8010/ITTY100
>> AUTOSTART: HTTP://INTERNET-TTY.NET:8030/AUTOSTART
>> <HTTP://internet-tty.net:8030/AUTOSTART>
>> EUROPE: HTTP://INTERNET-TTY.NET:8040/EUROPE
>> <HTTP://internet-tty.net:8040/EUROPE>
>>
>> On Aug 6, 2023, at 7:31 AM, Paul Heller <paul0926 at comcast.net> wrote:
>>
>> I remember a discussion years ago where a number of folks said high
>> voltage was important for the contacts. The design voltage was much higher
>> than 15v. You might try a loop source that delivers higher voltage and
>> 60ma. That might work better with your contacts.
>>
>> Paul
>> W2TTY
>>
>> ITTY: HTTP://INTERNET-TTY.NET:8000/ITTY
>> <HTTP://internet-tty.net:8000/ITTY>
>> ITTY 100:  HTTP://INTERNET-TTY.NET:8010/ITTY100
>> AUTOSTART: HTTP://INTERNET-TTY.NET:8030/AUTOSTART
>> <HTTP://internet-tty.net:8030/AUTOSTART>
>> EUROPE: HTTP://INTERNET-TTY.NET:8040/EUROPE
>> <HTTP://internet-tty.net:8040/EUROPE>
>>
>> On Aug 6, 2023, at 7:27 AM, Jeffrey Golas <jeffg at junknet.net> wrote:
>>
>> 
>> Dont use sandpaper! The MA is important as it does affect the waveforms.
>> The machine wants to see 60ma whether it's 120vdc or 15vdc. Set the scope
>> to be wide enough to get an entire character if you havent already, it
>> almost looks like the pic may just be showing the stop bit (33ms?).
>>
>> Dial in the loop first, verify its 60ma at idle.
>>
>> Jeff
>>
>> On Aug 6, 2023, at 9:05 AM, Eric Moore <mooreericnyc at gmail.com> wrote:
>>
>> 
>>
>> https://deramp.com/downloads/teletype/Model%2015/loop%20interface%20board/Schematic%20Rev%20A.pdf
>>
>> Verified the printer loop at 60ma. The keyboard loop runs at 15V, not
>> sure on the ma, but not sure it matters much as it just opens and closes
>> without driving any coils or similar.
>>
>> I am fairly certain my issue is the contacts somehow. I see voltage (and
>> continuity) up to those contacts, but despite cleaning fairly extensively
>> with contact cleaner, they are still too high resistance. I am going to try
>> some sandpaper today and see what is what...
>>
>> -Eric
>>
>> On Sun, Aug 6, 2023, 12:10 AM Gerry Block <gblock at sbcglobal.net> wrote:
>>
>>> typo:  "60 ma"
>>>
>>> Sent from my iPhone
>>>
>>> On Aug 5, 2023, at 10:07 PM, Gerry Block <gblock at sbcglobal.net> wrote:
>>>
>>> eric
>>>
>>> what does your loop schematic look like?  sketch it out and enclose
>>> photo.
>>> what is the loop power supply voltage.
>>> what is the series resistance to make the 60ms.
>>> are you sure it is running at 60 ms?
>>> where is the scope probe grounded and where is the loop supply grounded?
>>> i doubt it is the contacts.
>>>
>>> gerry
>>>
>>> Sent from my iPhone
>>>
>>> On Aug 5, 2023, at 5:49 PM, Eric Moore <mooreericnyc at gmail.com> wrote:
>>>
>>> 
>>> I have cleaned with contact cleaner and paper tape pretty extensively,
>>> but can always go another round.
>>>
>>> I do not think that is a good waveform, but similarly, no idea.
>>>
>>> -Eric
>>>
>>> On Sat, Aug 5, 2023, 7:23 PM Jeffrey Golas <jeffg at junknet.net> wrote:
>>>
>>>> Correct me if Im wrong but could just be "dirty"; as the cam rubs
>>>> against the switch youre seeing noise like a dirty volume pot.
>>>>
>>>> Id use some alcohol and a business card and scrub the contacts (plus Im
>>>> not sure thats even a terrible signal for a 1940s device. Going machine to
>>>> machine I dont think that tiny bit of leakage woulda mattered.
>>>>
>>>> Again, correct if wrong, Im here learning too.
>>>>
>>>> Jeff KC3GJX
>>>>
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