The Operator Information Area (status line) across the bottom had a symbol and the number 3, which the User Guide for the terminal gives as the error "Keyboard not attached or functional". That is indeed the condition here as I don't have a keyboard to attach. The three keyboards I have are the type with a rectangular connector to fit to the 3178, while this terminal uses a circular DIN style connector.
|Test mode but failing with keyboard missing error (3)|
RECOGNITION OF THE TEST SWITCH
When I put the terminal into TEST mode using the Test/Normal switch, it beeped a few times and showed the word TEST on the status line. No characters were displayed above the blue line. Upon reading the Guide for the terminal it became obvious that the keyboard error message above stops any further testing or action. Until I bypass that error or substitute a keyboard, I won't get any further.
I do have documentation of the pin assignments for the keyboard connector, essentially it has +5V, a clock and a data signal. I imagine I can work out the details of the protocol and enough to at least convince the Logic Element that the keyboard is present and working, although it might require a microcontroller or small FPGA.
An interesting possibility is if the keyboards I have for the 3178 use a compatible protocol, even though they have a different connector, I might be able to bridge one to the other. This is a bit more unknown that the paragraph above.
Finally, I still have an extraordinarily dim CRT at full brightness. As you can see from the picture taken with flash, with the terminal illuminated the blue line is swamped, same as with daylight.
Blue line almost invisible in bright lighting