As I recall, even if the CPU is locked up the 7-segment display will
show something - perhaps an "8".
Please check pin 40 of the CPU - that is the /RESET pin. If it is close
to 5VDC then /Reset is High, which is running. If it is close to 0.0VDC,
then /Reset is Low and the CPU can't function. The "/" in front of
"Reset" is the Active state, in other words, Reset is active when Low.
It should only be Low if the 12VDC power is under around 8VDC or
something else is defective. It pulses Low when power is available for
perhaps 1/2 second or less, then goes High to allow the logic board to
If /Reset is Low, please double check that the CPU has 5VDC present.
Just because power is at the connector wires, doesn't mean it is getting
through to the logic board. Connector pins and wires break in