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Looks like pin 25 (IR7) is hooked up to the MC6845 CRTC's vertical-sync pin.

I've got some video output, but it wasn't quite as exciting as I was hoping:

PCB in my hand, I can search for the desired tracks on the board!
I8259 - 18pin connect to mc6845 40pin(vertical sync)
19pin connect to AM9513(U45) 4pin
20,21,22,23,24 connect to 74ls14
25 to ground
do you need to track the connections further?

Right, I did make one further discovery this past weekend, which was that my assumption that IR7 was vsync was wrong: IR7 is actually the only interrupt that's always disabled, and IR0 (pin 18, as you observe) is the only one that currently makes the machine move forward. Except all that happens is it fills the screen with the character "6" and glitches out heavily in an infinite loop.

Pins 20-24 being connected to a 74LS14 means those interrupt lines probably need to be inverted due to the chips involved supplying their own interrupts with inverted polarity.

74LS14 is a hex inverter. The output pins are 2,4,6,8,10,12. So some combination of 5 of those pins would be what are connected to 20..24 on the 8259.

The corresponding input pins on the 74LS14 are 1,3,5,9,11,13. Which of the pins on the 74LS14 go to pins 20..24 on the 8259? And what chips feed the corresponding inputs on the 74LS14?

Are you sure that it's pin 4 of U45 that is connected to the I8259 pin 19? Pin 4 on the Am9513 is an input pin, so that doesn't make sense. Are you sure you don't mean pin 37 on the Am9513, which is on the opposite side, but is an output?

"666" He hints to us about his intentions! =)))

I8259 (U19) - 18pin connect to mc6845 40pin(vertical sync)
I8259 (U19) - 19pin connect to AM9513(U45) 4pin and connect over two serial Schmitt trigger (74ls14 - U59) to external connetor J2-30pin
I8259 (U19) - 20pin connect over one Schmitt trigger (74ls14 - U58) to D7201C(U35)-28pin = Serial port 1 INT
I8259 (U19) - 21pin connect to 74F02(U17) 10pin. U17- 8,9pin connect to RN1 (4k7 to +5V) and D7201C(U27)-28pin = Serial port 2 INT
I8259 (U19) - 22pin connect over two serial Schmitt trigger (74ls14 - U59) to external connetor J2-17pin
I8259 (U19) - 23pin connect over two serial Schmitt trigger (74ls14 - U58) to external connetor J2-11pin
I8259 (U19) - 24pin connect over one serial Schmitt trigger (74ls14 - U58) to external connetor J2-13pin BUT CUTED and connect to 40PIN (INT3) MULTIBUS SLOT Connector
I8259 (U19) - 25 to ground

You're not lying... with the vertical sync interrupt hooked up, and the NVRAM checksum test passing, this is all that the system does:

[video:youtube][/video]

So yeah, looks like you're right, I'm going to have to get the Z80 to work.

But I'm still not sure how the system forces the Z80 to boot where Robbbert said that the correct boot code is located...

Why do you doubt it?

Because that's not how the Z80 works.

if there are any ideas, then I can look at the board for what is connected.
Also i can try put on the board of ICE Z80 https://github.com/hoglet67/AtomBusMon , I have it! And dumped all activity Z80.

Ooh, that would be nice! Please do a trace of the first 10 or so Z80 instructions from power-up.