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IBM 3101 Terminal Monitor Help

RHopple

Experienced Member
Joined
Nov 30, 2017
Messages
55
Hello everyone! I believe I posted this in the wrong category so here it is in the hardware help page!

I recently picked up a IBM 3101 terminal monitor for cheap and thought it could be a fun project to get it working. I have experience making VGA video generators, so I know some things about sync signals and timing but Im certainly no expert. I thought it would be fun to try to power the monitor with TTL logic, maybe even a 6845 CRT controller (which I have from previous projects), or even an Arduino. The problem Im having is that I don't know anything about the monitor. I have scoured the internet trying to find a technical manual, but all I can find are documents about service of the actual parts and customer documents. One of the documents actually gave the pinout of the monitor connector, which I have attached as a screenshot. However, I cannot find anything about the horizontal frequency or the logic level (TTL or other). From what I can tell though, it looks very similar to the IBM Displaywriter monitor (has the same pinout) and the IBM 5151 MDA monitor.

I have tried a few things to get the monitor to work. After cleaning it out a bit I powered it up with +12 and +5 volts, and the tube heater glowed and I could hear a fait high voltage hum. This was encouraging but unfortunately I could not get anything else to work. I tried an Arduino and the MC 6845 I mentioned earlier, but nothing shows up on the display. I am willing to accept that the monitor is just dead as it has a lot of screen burn so its probably a high hour unit. But theres a ton of variables like getting the correct sync frequency or logic level. Any advice would be appreciated. It would be really great to find a technical manual that shows the frequency and what not.

Screen Shot 2021-05-29 at 9.11.37 PM.png
 
No, unfortunately I do not have anything but the monitor. I wish I had the actual unit so I could probe the signals which would make it much easier, but alas I do not.

I saw a redditor who had one of these complete units working (connected to modern machine) and so I messaged him to see if he wanted to help. He was really nice and sent several high res photos of the terminal's logic board, but he did not have an oscilloscope to test the pins. However, this provides me with some way of reverse engineering without the physical board. At least I found the pixel clock (14.1523MHz), so that at least helps.
 
Ah, the bane of our times. Keyboard collectors--rip out the guts and install an arduino to get it to USB and then flog the keyboard-less terminal. Sorry, I can't really help, any more than I can help on replacements for the keyboards stripped from Displaywriters.

Nothing like making junk out of vintage kit. Sorry, but I don't see the logic in it.
 
Are you saying you don't see the logic in the keyboard collectors or me trying to get the monitor to work? There isn't much point to what Im doing other than the fact that I just like getting old things to work. I found a few bad caps on the analog board so Im going to replace them before I try anything else.
 
My gripe is with the keyboard collectors. But it's kind of pointless in your case, since it's not likely that you'll be able to snatch a keyboard for your terminal. After all, we don't know how dependent the 3101 circuitry is on the keyboard being present.

You could always reverse-engineer a schematic; dump the firmware and see...
 
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