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?
Check the 5V at R1 - maybe it is shorted keeping the signal high ?
Can you bend pin 4 (so it is out of circuit) and see if it stays High on the CPU leg, then check the socket (in circuit).
I'm going off a schematic for a SYS80b - but it sounds the same.
