[GreenKeys] Associated Press Teletype maintenance; UPI As Well

[COURYHOUSE at aol.com]

George -   great  EXTEL info!  Will add  this  top our files...
I heard that the  dot matrix print heads for these early  printers 
were EXTREMELY  expensive.   do you remember  what they 
valued them at?   
 
Several  people  thought EXTEL invented  dot matrix printer technology IS 
THIS  TRUE?

Extel made a crt/keyboard/printer with some  logic in a box  not really a 
computer but a communications   terminal... a tty replacement.  by then they 
went to using the  Okidata  printer.... We do have a set of manuals  for 
this   ensemble. The fellow  who contributed this  unit to SMECC said  the cost 
of the  EXTEL heads  made the Okidata more  economical..??(??)
 
Thanks Ed# _www.smecc.org_ (http://www.smecc.org)  
 
 
 
In a message dated 11/20/2016 11:56:04 P.M. US Mountain Standard Tim,  
w7tty at centurylink.net writes:

GO,  CHARLES RING!!!!!!

The Extels that UPI used were dismal compared to the  model 15.

A new Extel gave pretty fine looking print for maybe two  months, and 
then the fan was sprinkled with substance.

The problem  was with the print heads, and the cabling which coupled them 
into the  electronics.

The needle guides in the first iteration of print heads  were made of 
some very soft plastic material which wore quickly. The wear  manifested 
itself in that the "focus" of the needles changed as the  plastic wore, 
causing the vertical alignment to be come jagged and thus  began to be 
hard to read.

Focusing was accomplished by changing the  shims of the needle guide 
supports and thus realigning the vertical. It  only lasted a few weeks 
and had to be looked at again.

A second  generation print head needle guide had a much improved 
material, this  taking longer to wear, and focusing was modified by 
making the needle  guide supports adjustable so that the needles could be 
realigned three or  four times before a new head was in order. Wear was 
also reduced by  carefully filling the cavity behind the print head with 
a better  lubricant. I used Conoco Super-Sta, a #2 lithium-based grease 
with a  tackiness agent added that kept the grease pretty well where it 
should  be.

HOWEVER - - -

Another fault with the Extel print head system  was that the cabling was 
a flat cable with about a dozen conductors in it  that ran to the circuit 
board through an oval slot in the deck of the  typing unit, and plugged 
into the circuit board. The cable was held in  place with a clamping 
arrangement with a bend in it such that the cable  would not become 
sharply crimped as the print head ran back and  forth.

Extel blew it by not using sufficient cable to allow the radius  of the 
bend to remain a constant. As the head ran to the left the radius  of the 
bend would change (decrease). This imparted a situation where the  thin 
copper conductors of the cable would cold-work and thus harden,  making 
the copper brittle and ultimately shattering into micro-thin copper  
strips that as they wore would cause the resistance of the cable to  
increase until there was essentially no connection through the bent  
area, starving the needle magnet(s) and losing the ability to  print.

RCA hated it when we called for a replacement print head, as  they were 
expensive. Some of us techs learned how to replace the cable,  with a 
little extra length where it was needed, and would greatly extend  the 
useful life.

The Associated Press did some cables which were a  flat ribbon with the 
conductors composed of some mighty small gauge  twisted copper. I have no 
idea how well that worked out, as about that  time I won the Fur-Lined 
Pot and was sentenced to working on I/O Selectric  Typewriters for Air 
West, Wizard Of Avis, and CIT Financial  Services.

Extel also made a line of reperforators  that were  extremely quiet, but 
had their own Achilles Heel.

The punch blocks  were far more precise than the those made by Teletype, 
and therefor not  really field serviceable.

You could renew the tape supply of a model 14  by sliding the oncoming 
new tape under the currently running out tape and  they would keep 
chugging along. Do that with an Extel reperf and a new  punch block had 
to be put in. They were REALLY REALLY Expensive, and RCA  hated that, as 
well.

So  there....

W7TTY



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