I've taken the initiative to dig into the KD11-A Maintenance Manual and the Engineering Drawings a little bit. To say I am intimidated would be a bit of an understatement. This is a very complex machine that many smart people with engineering degrees designed. I like to think that I am capable of screwing in a lightbulb without hurting myself, but I do not have an engineering degree. My electronics knowledge is 100% self-taught. So I feel, I think somewhat justifiably, like I may be a little out of my league.
On the other hand, there's a sense of freedom in not really knowing how much I don't know.
Based on a suggestion from the Vintage Computer Forums, I've narrowed my search down to the console control logic that is located on the M7235 STATUS board. A first step is to try to figure out why nothing gets loaded when I press the "LOAD ADRS" switch. I have come up with a plan of attack that will hopefully rule out very simple things like improper cabling, and then gradually work back from the console itself. So, this will be the entry point of my puzzle, to trace the signal from this switch through the KY11 console board, up and over the 40-pin flat ribbon cable that connects the console to the M7235, and then into the control logic on the M7235 itself.
To aid in this, I have done the unthinkable in the modern age: I have printed out the relevant schematics and the maintenance manual on paper. That's right, dead tree format. I find it much easier to leaf through than trusting the painfully slow image-based PDF browser on my iPad, or lugging around my laptop. Plus, I get to scribble annotations right on the paper. Keepin' it old-school, as they say.
I will say that the maintenance manual is quite handy, now that I have started to get at least some minor understanding of the architecture. It goes hand-in-hand with the prints and describes in great detail the operation of each circuit. It's almost like getting a CSEE computer design course, only without the crippling tuition payments!
I won't be able to really dig in until this weekend. I have ordered a set of DEC extender boards (one dual width, one quad width) from Douglas Electronics, and I hope they will be here on Friday. I am also expecting a hex extender card that Jack Rubin was kind enough to lend me I should have that next week some time. Once I have these in hand the game is really on.