Model 28 TTY project...

Part Three - the work continues...
After the keyboard frame comes the inter-lock ball mechanism. Each of the operational keys have a wedge that interfaces with the balls, where the chassis stand is tilted back so they don't fall off the tang.
The interlock ball track assembly has been swung up into position so that each of the wedges is between it's two balls in the track.
Here the keytops have all been installed. Again - the chassis stand makes this job much easier - as one can see what they're doing without having to stand on their head. Problem discovered - either the plastic in the space bar has shrunken (most likely)- or the plastic in the keytop guide plate has - either way - the spacebar legs no longer pass through cleanly - and drag pretty bad. The Dremel will be used to clear some material in the guide plate - as there is nothing (practically speaking) that can be done with the space bar itself.

Between an emergency service call early this morning - and church - that only leaves Sunday afternoon... which is slipping by fast... but still - it's (almost) looking like a teletype again...

Speaking of coming along - what about Riceguy's TT-98?
Well - with the wiring issues finally put to rest (nothing like fresh by-pass caps.!)... the TT-98 is back doing it's thing.
And looking just as good! Well done Riceguy!... Motivation to move my project along - for sure!!!!
Back to the 28.
More keyboard parts installed. And the first bit of trouble. There are obvious mis-alignments and bent parts in the code bail latch and anti-repeat assembly. Another bad sign is that when the code bar bail is "latched" back - the code bars aren't being pulled far enough to the left to allow the key-code levers to clear the code "teeth". A bit of a "tweak" on the code bar bail latch (O-249 p/n 151186) and it now pulls the code bars far enough (barely - any more and it fails to latch). Now the keys work as they should - but there's still a problem: when a key is pressed- the key bail rotates as it should and releases the code lever bail latch lever (O-131 p/n 151008) - which then drops down - and should push the code bar bail latch down so that the code bail swings to the right - setting the code into the code bars - and releasing the clutch. That never happens. First - the lever hits "bottom" on the code bail before it travels down far enough to cause the code bar bail latch to release. Even more troubling - is that even when extra clearance is provided to allow enough travel - the code lever bail latch lever doesn't have enough "ooomph" to press the code car bail latch lever far enough (some extra tension on the spring (O-132 p/n 70388) is enough - and everything fires. Problem with that, though - is that my spring gauge shows the spring in the code lever bail latch lever is correct (3 - 5 ounces - measures 4). So more investigation is needed to determine what issues there are - and what parts may be needed. This is a VERY old keyboard - (I'm not sure if it's a "Mk I"; but there are many parts differences between this and a Mk II). It's late - and this is going to have to be for another day...
Close up of the trouble area...
If'n it weren't broke - wouldn't be as much fun.
Then again... if at first you don't succeed...

They say if you are stuck - take a break - then try again - and maybe things will be a bit clearer. That's the case here. Didn't have but about an hour this evening... however - that was enough. Already had identified the symptoms pretty well... Now to diagnose the cause(s). First - we knew that the code bail latch lever wasn't pushing down far enough. What if we "adjusted" it a bit (a couple of big wrenches applied ever so carefully) raising the far end a bit. Well now it travels far enough to push the code bar bail latch enough to unlatch the code bar bail. However - it still need some "help" - the spring just isn't enough on it's own. It doesn't take much - but some thing's still not right. Notice in the pictures above the code bail latch roller - and specifically the felt oil washer between the roller and the "C" clip. Turns out that sucker is as hard as a rock - and is (almost) preventing the roller from turning. Now teletype used as few ball and roller bearings as they could - but this is one place where they wanted very little friction - so the roller rides on a set of needle rollers. - Teeny-tiny ones to be sure - but they are there for a reason - and having a hard felt oil pad impeding the rotation isn't good. So out it all came - degreased and checked the rollers - very smooth -and turns effortlessly. Clean, oil and re-install the felt washer and the roller doesn't want to turn. So new felt pad is cut to size - oiled and installed. Now the roller turns effortlessly - and the spring is plenty to operate the latch on it's own. Adjusted the code bar bail latch itself to move the code bars left just a bit more - now the "code teeth" are centered over the key levers. But nothing is ever simple. Now - the code bar bail doesn't quite latch - fortunately there is an adjustment for that - and even with these adjustments the latch releases as it should. But up jumps another problem: Now when the keyboard shaft is operated pretty fast (well as fast as can be hand spun) - the key lever bail flips on over too far. Normally - the lower stop on the code lever bail latch lever prevents it from rotation too far forward - however - now the code lever bail latch lever is traveling too high - and the tang on the bail is sailing right past. Remember that "tweak" a bit earlier - turns out it was about a 1/32 of an inch too aggressive - and needed a bit of correction. Now the keyboard is operating as it should. Of course the real test will be "at speed" - but that'll have to wait until we get some more work done. Working well enough for now - if it turns out that it won't "hold" at speed - then fresh parts will be in order. But that's for another day.

Site contents copyright © 2008 Randy Guttery
Back to Comcents...