[GreenKeys] TT-76C Help/Repair

[Duncan M. Brown]

Mark,

(I started writing this and then the computer lost it and I had to start
over!)

I am posting this to Greenkeys also, as it may be of interest to others.

If you want to ship it to me, I can look at it, but shipping will be
expensive.  With the manual and some time, you can probably figure it out
(unless something is broken).  Usually just needs a little lubrication
and/or adjustment.  Sounds like you are making a little headway.

On the difference between 20 & 60 ma:  there is a "Bias" winding on the
selector magnet that works as a magnetic spring on the armature.  When you
want to change from 60 to 20 ma, there are TWO plugs and/or connectors that
have to change (not user friendly). If you only changed one, things wont
work right.

Sounds like the selector lever & typewheel are turning and the problem is
in the "selector mechanism" (armature, selector levers, y-levers,
t-levers).  

You said "So the shaft is not frozen and does turn when a key is truck."
This implies to me that the amarature is moving in response to the pulses
from the keyboard and allowing the camshaft under the selector magnet to
rotate. So the problem may be that the selector levers are not moving in
response to the amature moving up  & down.

There are 5 selector levers that are set by the armature moving up & down
with the signal pulses. The positions of the 5 selector levers are
transfered to 5 y-levers and their positions are transfered to 5 t-levers. 
The 5 t-levers are then pushed up to rotate 5 code bars in the code cage.
The position of the 5 code bars allows one stop bar to move in and stop the
selector arm at the proper place to type the desired character. (see manual
for details)

One of my favorite test (on any TTY) is to manually operate the selector
magnet's armature up & down. This should release the clutch to allow the
camshaft to turn and if you continue to move it up & down, some random
letters should be printed.  If moving the armature alows the camshaft to
turn, but the selector arm & type wheel does not change, then either the
armature is not releasing the selector levers or the selector, y- or
t-levers are stuck. Or the mechanism (transfer lever) that moves the
t-levers up to the code cage is not functioning. There is an adjustments
for the armature & transfer lever - see the manual.  As I remember, you
should be able to move the selector levers & y-levers by hand.  If not,
give them some light machine oil.  If they are really gummed up, they may
need to be dissasembled.  See manual and follow it closely.

I don't know what you are referring to by "The lower magnet by the
keyboard".  

Troubleshooting remotely is always difficult, especially if you don't have
another machine to look at.  (Hardest of all is troubleshooting opver a
full-duplex link where you cant see what you have typed!)

Hope this helps, let us know how you make out.

  --Duncan


> > Back again, I removed the inking ribbon assy to have a better look at
> the code wheel, shaft etc, I was able to "reset" the fingers that
> determine the code on the wheel, when I did I was them able to rotate
> the shaft untill it rested on the selected code.  So the shaft is not
> frozen and does turn when a key is truck.  It looks to me now that for
> some reason the fingers controlled by the electro magnet never change
> code or reset.  The lower magnet by the keyboard does change position
> with each key selected, I just don't see how the information gets from
> one place to the other.  The other thing I just discovered is that when
> I changed the Ma setting to 20Ma once a key is pressed it goes full auto
> and won't stop, change it back to 60Ma and it works as before.  Seems
> like I am fighting an uphill battle here.
>
> Mark