ASR33 Problems - test-drb@ccmp.vtda.org

12 Nov 2002

...
 From: "David Comley"
&lt;david_comley(a)yahoo.com&gt;

 Hi
I think you need to make this point clearer. When a character
 is punched, the same character is miss printed on
the platen?
 This is how I read his original post. 
Even using the REPT key to workaround the codebar
issue, I wasn't able to connect the carriage problem
conclusively to either a rotational or a vertical
problem. I think at this point I'm going to take the
carriage off again and try a more thorough
dismantle/clean/oil. Once I resolve the codebar issue
it will be easier to diagnose the carriage problem
with a clean mechanism.  

 This tells me it is something sticking in the
linkage that goes
 between the code bars and the print head( or he
has it installed
 wrong but that doesn't explain why it starts
working with repeats ).
 I would remove the print assembly and put it in
some solvent
 while moving the levers. Then clean it off/dry it
and re-oil
 it. You most likely have some dry oil that is
sluggish. Getting
 oil into the right place will take a bit.
In the service( military ), we used to clean things in a bath
 of water and heavy detergent. This was done in an
ultrasonic
 cleaner. We'd then rinse and bake it at about
150F for a few
 hours. Then Re-oil/grease, place on test bench and
fine adjust.
 I suspect that a good dish washing liquid would
work. 
I remember using an arklone bath at a place I worked
years ago for cleaning circuit boards. Probably taken
a few years off my live expectancy breathing that
stuff in.

Basically, there are 3 possible problem areas : 

1) The keyboard contacts are not closing correctly, so the parallel data 
 output of the keyboard is incorrect.

2) The distributor disk (rear right of the typing unit) is not correctly 
 serialising the data from the keyboard. Unlikely,
but possible. 

3) The selector unit (rear left of the typing unit) is malfunctioning, 
 and is not correclty responding the receiving
magnet.

I can see the armature 'stutter' when I punch the
rubout key - by stutter, I mean that its movement
looks slightly different between keypresses. So I'm
inclined to think that the magnet is just responding 
Hi
 You haven't made it clear about punching. Does it work
correctly when you use the punch?? If it does, it can't
be the keyboard, distributor or codebars. All of these must
work to have the punch work correctly. The punch is
mechanically connected to the code bars of the printer.

...
 to what it is receiving which is incorrect. I cleaned
the distributor and reseated the brushes, readjusted
the brush holder to the alignment mark per the
adjustment procedure in the manual. So I'm back to
option 1) - the keyboard - as the source of the
problem. One thing I noticed last night was that the
keyboard cover is broken. There are four round tabs,
one at each corner, that fit into corresponding holes
on the end plates. These are broken, so the cover can
rock from side to side, pivoting on those center
projections. I wonder if that could cause some sort of
alignment problem within the keyboard ? 
 I'd think it would have to shift quite a bit to fail.
It would be more likely that the switch contacts( at the
right side of the keyboard ) might be dirty.
 For the pegs, one can drill the plastic and use some
dowel rod( wood or plastic ) from the hobby shop to
replace the alignment pegs. Since this had a punch on it,
it most likely has a lot of chad stuck on things that can
gum things up.

...

Thanks for the suggestions - I will get to it again
tonight and see what else I can find out. I hate the
idea of opening that keyboard up... 
 As I stated earlier( in this group  ), you can disconnect
the power from the motor and run things slowly to see what
is missing. You just have to manually lock up the clutches
since it isn't spinning fast enough to lock them with inertia.
Dwight

...

Dave

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