THE TOGGLE SWITCH
On the console next to the power on switch is a toggle switch labeled Console and Keyboard. Its only purpose is to set a bit that is read in the Device Status Word (DSW) of the control keyboard/printer. Software should look at this bit to decide whether to take input from the keyboard or to instead read the console entry switches that sit on the faceplate of the typewriter. This is completely voluntary, the only thing done by the 1130 is to set the bit.
PROBLEM OBSERVED
When I was running the hand loop to look at characters entered on the typewriter, I could see the DSW and that bit 3 (the toggle switch) was always on regardless of the physical position of the toggle.
I had thought that the switch contacts might be tarnished, but when I had the machine powered up and measured the pin at the output of the debouncer circuit, it was appropriate responding to the toggle switch. The readings were -3 and +5, which is the result of the debouncers, but those two values are completely acceptable as input into an SLT logic gate whose low and high levels are defined as 0 and +3V.
When I looked at the pin that this signal should be directly linked to on an adjacent pin of the card, the voltages were not there. A continuity check confirmed that the board (backplane) which should have a trace between the pins was defective.
REPAIRED
A bit of wire wrap restored connectivity of the two pins. The DSW now shows the accurate state of the toggle switch.
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