[GreenKeys] Model 33 Keyboard

[Jones, Douglas W]

On Jan 19, 2016, at 1:03 PM, Michael Zahorik wrote:

> Correct me if I'm wrong. I believe that the keyboard works as follows.
> 1. the user presses a key
> 2. the key lever pushes down some code bars
> 3. some the code bars transfer and trip the Universal lever.
> 4. the universal lever allows the contact bail to rotate and allows the contact wires to work.
> 5. Here I'm a little foggy, I think that the contact wires present a parallel representation of the key to the distributor. Not sure how the distributor knows when it should work.

Right.  The universal lever rotates the H-plate (really X shaped) that pulls an extension lever that goes under the typing mechanism back to the distributor.  Pulling that lever trips the distributer clutch to convert the parallel data to serial form.  At the end of its rotation, a cam on the distributer pushes back on the universal lever, resetting the keyboard.

> 6. the distributor converts the parallel code into serial code.
> 7. once the serial code has been sent then the Universal lever is tripped and the contact bail opens the contacts wires. Also not sure how this works either.
>  
> Next I tried to measure continuity of the contact wires to the J7 plug. I got nothing, all open or very high resistance. Looking at the right side contact wire assembly, I found the that the lugs connecting to the terminal bar were badly corroded.

On -33 I am restoring, the plastic body of the contact block had some broken tabs, so we bought a new-old-stock replacement and then carefully mounted the contact bars and wires on it.  That was tricky, we took close-up before and after photos and compared them carefully in order to make sure all the bits were in the right places.  The best of the photos are here (the contact block discussion is after a discussion of power supply wiring):
-- http://www.cs.uiowa.edu/~jones/pdp8/UI-8/log2015a.shtml#2015-01-30

> I also found that one of the terminal bars was loose. See picture. I can either clean or replace the lugs and I figured I would glue the small terminal bar back onto the terminal assembly with epoxy. Any thoughts?

As I said, we replaced the plastic block.  NOS parts may still be available.

> Also how should I clean the contact wires and terminal bars?

Soap, water and a toothbrush isn't a bad place to start.  I wouldn't recommend any heavy abrasives.  Perhaps this is a good place to use a contact burnishing tool (see the recent thread on that subject), since that's going to have a lighter touch than any other abrasive I can think of.

If your assembly has rusted, the 12 springs in the assembly will need close inspection.  They are fine, and even a little rust can be enough to wreck them.

		Doug Jones
		jones at cs.uiowa.edu