[GreenKeys] TeleType Model 33 Not Sending Some Control Characters Correctly

[Robert Jarratt]

CTRL-G works as expected in LOCAL mode, ringing the bell. But if I press
CTRL-C it prints a C. It does seem as if bits 7 and 8 are swapped, but if
that were true it would never have worked, and yet previously it has worked
fine.

 

The only thing that comes to mind now is that I did take the typing unit out
not so long ago, could I get this problem if I didn't put it back properly?

 

Regards

 

Rob

 

From: Teletypeparts [mailto:teletypeparts at aol.com] 
Sent: 27 October 2013 17:40
To: deramp5113 at yahoo.com; greenkeys at mailman.qth.net;
robert.jarratt at ntlworld.com
Subject: Re: [GreenKeys] TeleType Model 33 Not Sending Some Control
Characters Correctly

 


Rob,

 

Mike is dead on with his diagnosis.  More detail than I have ever looked
into.  Sometimes the twin wire contacts arent opening and closing fully when
they should.  Its a swap sort of.  One opens and the other closes.
Sometimes you have to bend one of them ever so slightly to accomplish the
required action.  

 

A good test is to be in Local mode and use the Bell feature.  You will know
immediately what is happening.  

 

Mike, 

 

Did you enjoy your trip to Vermont?  I think you had good weather.

 

73,

 

Wayne

KB1FDW 

 

-----Original Message-----
From: Mike Douglas <deramp5113 at yahoo.com>
To: greenkeys <greenkeys at mailman.qth.net>
Sent: Sat, Oct 26, 2013 10:05 pm
Subject: Re: [GreenKeys] TeleType Model 33 Not Sending Some Control
Characters Correctly

Robert,

 

Sorry it took so long for me to jump in - I've been out of pocket for a
while.

 

If you have levers and contact wires on the left side of the keyboard that
move with the control and shift keys, then yes, you have a parity keyboard.
Also, your problem is clearly correlated to parity.

 

Note that every character you're having problems with has the parity bit set
when control is not pressed. The control key is supposed to open the bit 7
path to make it a zero and then invert bit 8, the parity bit. It sounds like
the contact wires on the left side may not be arranged exactly right in the
plastic sliders and somehow the parity bit is ending up in bit 7. Can you
get a really clear close-up photo of the left side contact wires for me? Can
you tell me what is received for Bit 8 when you press a C and a Ctrl-C, for
example?

 

Mike


 

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