Building the new MOSFET switching board for the 1053 Emulator - almost done

MOSFET SWITCHING BOARD CONTROLS FOUR FEEDBACK SIGNALS TO THE 1130

The IO Selectric typewriter that is the basis of the 1053 console printer has microswitches that control four feedback signals - End of Line, End of Forms, CB Response and CR-LF-Tab Interlock. Three of these signals deliver +12V or are open circuits, while the CB Response signal delivers +48V or is open. 

My switching board design uses P channel MOSFETs to act as the microswitches, controlled by a 0 or 5V logic output from the Arduino inside my emulator. An NPN transistor controls the gate of each MOSFET, either leaving it at the supply voltage (12 or 48) or dropping it enough to switch on the MOSFET. 

For the three signals that are 12V level, I used an MPS2222A transistor but that won't work for the 48V signal. Every NPN transistor I had in my shop had a maximum voltage between emitter and collector of 40V or under. In operation, with the MOSFET turned off, the transistor will see the full 48 or 12V. 

I chose a BD139 transistor, which has an 80V maximum Vce rating, but had to order it. It will arrive tomorrow afternoon when I can add it to the board and wire this into the emulator.

Repaired Calcomp 565 power supply and pen up/down circuit

REPLACED DEFECTIVE PARTS AND RESTORED OPERATION

I wasn't ready to hook up the cabling that runs to the carriage and powers the pen solenoid, but I could insert a 10K resistor between the two terminal that feed the carriage cable ends. I first verified all the power supply voltages - +3, +1.5, -7.5, -9 and -24 - were correct. I then checked out the pen up/down circuit.

The circuit is a flipflop that can be triggered by commands from the IBM 1130 as well as from a switch on the front panel of the plotter. I verified that the switch is setting the flipflop to the condition being requested, and that the power flows through the 10K resistor when the flipflop is set to the on state. 

MECHANICAL ISSUES REMAIN TO BE SOLVED BEFORE THE PLOTTER IS RESTORED

The cables that pull the carriage, with the pen solenoid atop it, left and right are connected in the rear of the plotter by a spring that maintains the appropriate tension. I don't have the spring. Peers who have a working plotter measured the spring's size and force, which means that I can find a decent substitute. I have yet to do this.

The drum surface was dented and partially repaired, but it is still out of "round" and has a few high and low spots. I need to get this aluminum piece reshaped to an acceptable degree or I have to build or buy a substitute. It has pins on each side that provide tractor feed for the special paper rolls that are used with this unit. That is the hard part about finding a replacement.

I don't have the paper with pin holes that this uses. The roll is 12" wide, 120 feet long and has pin holes that are .375" center to center spaced down the sides of the paper, with holes that are .13" diameter. 

Finally, the Calcomp solenoid I have is for a cutter rather than a plotter. It used the same drum mechanism and carriage as the 565 but had a cutting tip that the solenoid would hold up or drop down onto the material being cut. Since the body of the solenoid and its electrical characteristics are identical between pen and plotter, I only have to design and machine a way to put a pen inside. Work still to be done on this aspect of the project.

When all of the above are resolved, I can wind the cables around the pulleys and attach the spring to allow the carriage to be moved left and right during operation. This sounds easy but the task of winding the pulley on the right side of the machine, as viewed from the front, is quite challenging. It is an operation that would require 4-5 hands working in close proximity to a pulley that is only about 2" diameter.