I sent this to Marco, but I thought Maybe I should post it here as well to keep the thread intact should someone else be trying to fix a similar problem in the future.
Apply power, with z10 pin 6 grounded, and....
Light comes on, seemed pretty bright!! Then went off for maybe a full second, then came on rather dim, at least in comparison to the first lighting.
Checking your docs, yes, pin 40 of the 6502. Has 5 (My multimeter set at 20v says 4.33v -is this a problem?)
Next, pin 37 is found to be pulsing- (I knew I'd use this logic probe eventually!) Yes, z3 is a DM7404N.
I read somewhere or other that double-zeros on the display (this was when the board was in the game) CAN indicate a bad 5101. Wouldn't surprise me as I'm given to understand that chip is subject to failure at the slightest static, or if someone so much as coughs on it.
Since the next tests seem to involve removing the 5101, I went ahead and removed him and put machined socket pins so I can plug and unplug at will. Unfortunately a new 5101 did not fix the issue, it still flashes once, and stays on.
I have not found another 6502 in my searchings so I've placed an order for a couple 6502s, and 4 of the RIOT chips. I see one of the pin-sites has a kit with these chips (1 6502, and 3 of the RIOT chips) so I've gone ahead an placed an order for those chips.
Does this seem like the next logical step? I mean, if the CPU can't get off the ground, even though it's got power, and a clock chip- That seems to point to that processor chip itself- I guess I can replace the 6502 first, and then if it still doesn't come alive, I could start with the RIOT chips. Or is it maybe better just to replace them all and be done with it? In some things- it seems like if you replace the broken one the next weakest link in the chain breaks. Would I be replacing for nothing, or gaining some peace of mind?