Working on a Lethal Weapon 3 that is not booting. The 5v LED and PIA come on and stay on. The Blanking LED never comes on. Power is good at the CPU. Board is very clean with no battery damage.

I pulled the board so I could work on it on my test bench. I tested the 27512 rom and it was good. I burned a Data East test rom and now when it boots the PIA LED comes on and then quickly goes out. Occasionally when I power it up the PIA LED goes on then off quickly and then comes on solid, which according to the documentation for the ROM that means a bad checksum on the ROM. I tried swapping out the CPU with no change. I tested the 6264 RAM and it's good as well. I also checked both the ROM and the CPU socket with my meter and all pins ohm out fine.

Using my logic probe, I'm seeing the following on the 555 timer:

1 - low
2 - high (not pulsing)
3 - low
4 - high
5 - high (not pulsing)
6 - high
7 - low

According to the pinball wiki, pins 2 and 5 should be pulsing and pins 3 and 7 should be high. Based on those readings, it sounds like the 555 is not getting a signal from the PIA at 11B. Is there a good chance that PIA is bad?

Any info would be appreciated. Thanks.

Using my logic probe the CPU seems to be running. I'm getting a high signal on pin 40 and a high/low pulsing signal on pin 39. I thought perhaps one of the two 74LS244N's were having issues but I piggybacked a 74F244N (didn't have an LS, from what I read the F instead of LS should be ok) but no change.

Not really sure what else I should be looking at. Anyone have any ideas?

I figured it out. Using the schematics and my meter I found an open circuit between pin 13 (A4) of the 6802 to pin 6 of the 74LS244. Flipped the board over and sure enough there was a really tiny nick in the trace that connected those two pins. Ran a jumper wire and now the test rom is running!