Tuesday, December 16, 2014

Console printer adjustments and restoration almost complete

Tomorrow I have obligations at both the Computer History and Digital Game museums, plus an appointment for a haircut, really constraining my available time with the 1130, but I should be back at the machine in earnest on Thursday.


It dawned on me that my assumption for the restoration, that this was properly adjusted before it sat in storage, is not correct. I see the typeball triangle on the top plate, which should point directly at the platen when at rest, is rotated 5-8 degrees to the right instead. This is undoubtedly causing the issue where the detent bar can strike the tip of the tooth and not enter the proper notch on the typeball rim.

Incorrect home position of typeball, rotated a bit to the right
My early operation of the console, which yielded the correct characters for every position on the ball, lulled me into believing my assumption of correctness. Visually, however, I see it isn't so.

Print shaft gear with setscrews, adjust rod to proper position then tighten these up
The rotate arm should be directly vertical when the typebar is in the home position (at rest), but it is tilted so the top is a bit to the right of the pivot at the bottom, leading to the incorrect home positioning. The adjustment for the rest position is a turnbuckle on the rod that connects the mechanism selecting the rotate amount to the rotate arm.

I hate the idea that I might start adjusting the rotation position but have ignored some 'earlier' adjustment which may be off spec. I believe I have to at least do a quick validation of the adjustments starting at step zero, in sequence, since each adjustment builds off prior ones. Adds a bit more time to this particular restoration but ultimately worth it.

I also see the belt and motor oscillating, showing that the corroded slots on the motor pulley are not allowing the belt to fit into the slot. This raises the belt as the pulley rotates to put the bad slot at the furthest point from the main pulley, increasing tension on the belt, bending the motor forward on its shock mounts, and thus generating the oscillation. It has to be replaced by a good motor pulley - fortunately that replacement will not require any disassembly of other parts of the printer, only loosening of the motor mount screws.

Several hours of careful work gave me proper timing for tilt/rotate, print and filter shafts and everything else except for the C2 contacts that indicate when the mechanism is busy during a print cycle - it should break the connection at 20 degrees of rotation and restore it at 120 degrees.

Timing of C2 contacts
C2 contacts in situ, continuity tester connected by colorful alligator clips at bottom
Adjustment screws - oval slots but no positional adjusters, just hand movement
Another view of contacts
The contacts were a bit oxidized, only conducting sporadically. I used my burnishing tool to strip off the oxide layer, restoring proper operation. Adjusting the contacts to make and break at the proper degree positions was challenging. I could get one or the other point working, but the opposite state change would be too far off its target. I ran out of time today but will be attacking this further in the coming days.

Burnishing tool for oxidized contacts
I found the cause of the carrier return problems - I had dressed some wiring with a cable tie which interfered with a rod used to absorb the energy of the carrier hitting the left margin. This machine has a special feature called High Speed Return installed, rather than the usual mechanism and return speed. It works fine now.

I included pictures of some special tools used to work on Selectrics - the Hooverometer, a spring hook which is used to install and remove springs, a set of bristol wrenches and a circlip installing tool. It is easy to mistake the bristol wrench openings for allen wrench openings, but using the wrong tool rounds off the points rendering the screws useless.

Hooverometer to measure separations and heights

C-clip tool, spring hook and bristol wrench set

I attempted to solder the teeny wires to the teeny pads on the fpga circuit board, but continued to have problems with each method I attempted to hold three wires simultaneously and rest them on their respective pads less than .01 inch apart.

I also contacted the maker of the board, based on comments in some of their documentation that suggests they can make repairs to the board, giving me a backup if I can't get this wired up myself. I found that the board I bought just 30 days ago is now discontinued, removing the option of tossing a few hundred dollars away on a replacement.

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