New CPU in, couple of this resolved but still IRQ high.
From reading the schematic, IRQ begins at pin 4 U1 (6502) goes via R1 & R2 to pin 16 TC1 then to pin 25 U4, U5 & U6. Is there anything prior to U1 which has anything to do with IRQ?
TO help you follow the 'flow' in the diagram, the IRQ signal is going
INTO pin 4 on the the 6502cpu.
( maybe this will help you follow signals with your probe/MMeter).
IRQ (Interupt ReQuest) is a signal that comes from all the other chips into the main cpu.
IRQ will pull low to interupt the main cpu(6502) to process information in the chip that interupted the cpu..
It's a way for an external chip to say to the cpu "hey, i have fresh data for you, stop what your doing and process
my data"
MM.
