Operational clutch trigger work on the 1053 console printer

GETTING BACK TO THE SELECTRIC

It has been a very busy few weeks with holidays, family obligations, volunteer work and my neighbor in the strip mall pushing hard to get me to relocate so he can expand his chiropractic practice. 

That involved lots of work evaluating properties and working on requirements so that I minimize the disruption to my shop work. Too, he will pay to do the moving of everything and I have to find a suitable replacement without any additional cost burden other than perhaps slightly higher rent. 

I have organized and placed most parts in labeled containers, which helps me while working and is also going to make a move be convenient as there will be no special packing necessary. There are so many tradeoffs and subtle requirements due to the heavy weight of some equipment, access door minima, power and air conditioning necessities, plus of course keeping the travel time between home and shop to a reasonable value. 

Commercial real estate figures can be quite confusing - some include public area space into the square foot they quote for a unit - and there are various lease types some with big downside exposures. Even after adjusting to the actual floor space, the usable area can be quite different. If a space is configured as multiple offices, there is wasted space in hallways and it takes a lot of planning to be sure that all my equipment and tables (19 of them) will fit comfortably. An open rectangle, on the other hand, is like my current shop and offers the most flexibility. Anyway, back to the good stuff working on computers for now.

OPERATIONAL CLUTCH TRIGGERS

The Selectric based console printer uses motor power to accomplish five movement functions - space, backspace, tab, carrier return and index (line feed). There are two clutches for these functions, one that completes its role in one-half a rotation of the main operational shaft and the other taking an entire rotation at a time. 

The carrier return and index functions need the full rotation to complete their work and are both implemented on the right clutch which turns 360 degrees when tripped. The other three are completed in a half rotation, 180 degrees, and share the left clutch. 

A long front to back plate is assigned to each of the five functions. It is held forward with a spring loaded latch, but when the front is pushed down it is pulled rearword by a spring. Any of the left three plates will trip the left clutch to take a half rotation. At the same time that a plate moving to the rear trips the clutch, it moves a lever so that when the clutch rotation moves a bail up and down, it pulls on that lever. 

Thus, the left clutch has three levers, controlled by the three long plates which trip the clutch. The particular plate that was activated causes its associated lever to be pulled down by the mechanical movement driven by the clutch. 

One lever will twist the escapement torque bar causing the carrier to be released for rightward motion which is stopped at the next column position. This is the space function. To push on the plate and let it move rearward, the console printer has two mechanisms. There is a solenoid with a link that pulls down on the plate to release it. There is also a lever driven by the Space pushbutton that pushes down at the front of the plate. Either of these activations of the plate cause the clutch to operate, the escapement lever to be pulled down by the bail, and the carrier move over one column. Just to add to the complexity a bit, there is a third way that the escapement torque bar is twisted, in addition to the lever powered by the operational clutch, This third method is a pull rod that is driven by a cam on the print shaft, so that at the end of a cycle printing one character, the carrier then moves right one column. 

The next lever when pulled down with twist the tab torque bar, which causes the carrier to lock all the pawls out of the rack teeth so that the carrier glides to the right. When a tab position is set at a given column, it pushes a release on the carrier so that the pawls snap back into the rack; this stops the carrier at the position which was set. 

The third lever when pulled down will force the backspace rack to the left, which forces the escapement pawl out of its rack and physically moves the carrier back about one column. The escapement pawl drops into that rack tooth one column to the left and we have accomplished a backspace. 

The right (full rotation) clutch has two plates associated with it, for carrier return and index. Just as with the left clutch, when either of these plates is released to move rearward, it trips the clutch to spin once. It also pushes a lever so that it will be moved down by a bail driven by the rotation of the right clutch. 

When the index lever is pulled down, it pulls on a set of ratchet teeth to move the platen (roller upon which the paper sits) up one line. Since each of the five plates has a solenoid that can trip it to move rearwards, the processor can command any of those plates by energizing its solenoid.

When the carrier return lever is pulled down, it activates a complex set of mechanical parts, including arming the margin bar to be tripped when the carrier reaches the column set as the left margin. It latches the carrier return operation to continue until the margin bar is tripped. The latched carrier return continues after the right clutch has finished its rotation, taking as long as necessary to move the carrier to the left margin. 

It pushes a nylon shoe down on a coil spring which has only one end fixed to the operational shaft. By stopping the coil from turning, it winds up, squeezes on the operational shaft and thereby turns the drums that pull the carrier to the left since the drum is now locked onto the operational shaft rotation.  When the carrier strikes the left margin that releases the latch which pulls the shoe from the spring. That disconnects the rotary energy of the operational shaft from the drum. 

At the end of the rotation of either of the operational clutches, a lever pushes the plates forward where they should latch into the idle position awaiting the next time the front is pushed to release a plate. One defect this console printer exhibited is that some of the functions were continually tripping the operational clutches and causing continuous movement. 

MISSING SPRING TO LATCH BACK IN THE IDLE POSITION, CHALLENGING ACCESS

The reason for the failure to stop after one rotation was that a spring at the front of the plate was missing. This spring pivots a small mechanism up to cause the plate to latch into its most forward position until pushed down at a future time. No spring, no latch, thus is remains rearward and trips the clutch repeatedly. 

These springs sit in an area with very limited access. All the parts that were added to allow three pushbuttons to trigger three of the five plates take up space right in front where I need to be. There is a button for Tab, one for Space and one for Return. 

The spring for the Tab function was missing, so that when a tab was requested by either solenoid or pushbutton, it kept retriggering. You can see the missing spring below, once I opened up access. 

missing spring

DISASSEMBLY OF PUSHBUTTON ASSEMBLY TO GAIN ACCESS

pushbutton parts are in the way

After hours fighting with spring hooks, powerful lights and almost no visibility, I realized that I would have to disassemble all the pushbutton related parts to free up space.  I pulled off all the parts and the difference is clear. 

parts moved out of the way

It was very easy at this point to attach the spring and verify that it latched the tab plate when it was returned forward at the end of one left clutch cycle. 

The spring is in place, pulling the latch to hold the plate forward

ALL FUNCTIONS LATCH BUT BACKSPACE NOT FIRING OFF CLUTCH

I reassembled everything but did notice that when I released the backspace plate, although it did release from the latched position, it did NOT trip the clutch. I am guessing that the spring which pulls that plate rearward is missing or disconnected. 

This is surgery that must take place in another area called the operational bracket which is near the rear of the machine but blocked by the mainspring and all the linkages that are turned when a lever is pulled down by a bail driven by a clutch. I have been successful attaching springs to the levers that are pulled by the bails, so I expect that I have enough access to accomplish this fix on my next shop visit. That should complete repair of all the movement functions.