Testing with a Calcomp 535 (equivalent of IBM 1627 model 1) - part 1

I WANTED TO USE A PLOTTER FOR A FINAL CHECK OF THE PROJECT

I am restoring a Calcomp 565 plotter and it is currently disassembled because the physical plotter drum is dented and unusable. However, I can connect to it and power up the circuitry to see how it responds. The stepper motors should move if it is responding to the -up or -left commands. I should see voltage to the solenoid that will raise or lower the pen - turned on when the pen is lowered and turned off when a -raise command has executed. I can also verify that it delivers the -24V to the 1130 when the power switch is turned on. 

CABLING WORK

I was not satisfied with the quality of the SLT connector mainly due to issues with the crimp pins particularly with a few wires that were larger (but had unique colors like orange and purple). In the end, I rebuilt the connector and fidgeted with the pins as some of them were not locking into place in the connector as they should have. 

I also discovered all the ways to assemble the Cannon 19 pin connector incorrectly - one at a time - but eventually got the threads, cover, access plate, strain plate and other parts over in the proper sequence over the wiring. In other words, the cable work took surprisingly long.

I finished wiring my cable to the 19 pin connector that plugs into the plotter. Four wires from the connector run to an SMS paddle card that will plug into the IBM 1130's power block, delivering 115VAC and connecting to the signal ground of the computer. The other wires run to the SLT connector plugged into slot N5 of compartment C1 of gate A of the system. I also included the 3.9K resistor that IBM installs on the signal SMS paddle card, since I skipped the signal paddle cards for this installation. The resistor is inline in the Cannon connector now, thus making the equivalent connection from the plotter to my controller card as would occur with the IBM paddle card scheme. 

My cabling between plotter and the 1130

Controller card and connector in place

MAKING SURE THE PLOTTER WILL POWER UP AND WORK (ELECTRICALLY)

Since I haven't powered this up since I received it years ago, I needed to approach it as a restoration to get all the electrical/electronic aspects working. Then the stepper motors have to be able to move when the circuitry commands it.

First up was the power supply, which I had to get working properly before hooking it to the logic and other circuitry. This supply produces -24V, -9V, -7.5V, +1.5V and +3V all from a single bridge rectifier, using diodes in a voltage divider plus one Zener diode to produce all the individual levels, with ground sitting 3V out from one end of the 27V span out of the rectifier. Not too much to go wrong, but had to be checked. 

The -24V output was sitting at -34V, but that may be because there is no load with the power supply disconnected from the logic board and other components. There is also the reality that line voltage in the US is noticeably higher than the nominal 115V that the equipment was designed to use. 

At this point, I noticed that the diagrams that I had printed, from the IBM 1627 version of the plotter manual, had components whose numbering was changed compared to the Calcomp manual; most importantly, the component numbers on the actual plotter matched the Calcomp manual. IBM chose to drop some diagrams from their version of the manual, but I needed those diagrams to do the detailed testing I had planned.

I will print all the diagrams from the Calcomp manual when I get home tonight, so that I can finish up my testing of the plotter power supply and move on to the other components.