Ugh, what is going on with the EPROMs and cpu?

When I see stuff hanging off of an IC socket I have to think it is stressing out the physical connection. Has that cpu socket been replaced?

CPU P40 = High / 5v for reset
TP6 / CPU P36 = pulsing, probably around 2.5vdc. clock
CPU P5 = Pulsing around 2.5v. VMA

The data buffers at IC 8 and IC 9 fail quite often and i see them still installed on your board. Typically these are changed to jumpers by the time fire power came out. Check the inputs and outputs of these buffers. THey should have near matching signals.

The address buffers go, but much less often, still pretty easy to check with a logic probe. (pull everything but the CPU to check the address buffers, they should be pulsing with no software installed).

If all the checks out i would try and run the test rom at IC17 and see if it runs (you would have to remove the combo eprom from the daughter board). Also can pull the other socketed ICs to make sure they are not locking up the board.

Is there any jumper instructions needed to make that CPU/EPROM daughter board work? I see some kind of logic IC doing chip select of some sort.

Your blanking, TP4, not being all the way low is suspect. When the board is not running the blanking should be all the way down at 0v (i think?). Attach a meter to blanking and cycle the power a few times and see if it changes at all.

Typically blanking not being high is a symptom of a logic problem, not the cause. But since you have a funny reading I would check that circuit. There is a 556 timer, a transistor of some kind, 1uF and .01uF caps and the input signal going in.

You can kind of cheat to see if the blanking is bad. I would pull the fuses for the lamps and solenoids and watch the displays. Briefly jump +5v to the blanking test point. If the game boots, for sure blanking issues. If the displays show scrambled, blanking is not the issue (or only issue i suppose). I bet a lot of people would tell you not to do this, so i take no responsibility if something blows up =D. Blanking is kind of a safety check that blocks displays, lamps, solenoids from working if the computer is not running.

A bad PIA or driver board issues could explain the blanking as well. You can remove the driver board and see if the MPU still is locked up.

Remove the driver board and only have the top left power plug installed on mpu, see if the diag runs.

When things are crashed, you get erroneous diag results, the software has to be running somewhat for diag.

That indicates a MPU problem. If your blanking is still anything besides 0v or 5v, i would check that circuit. I think i the 1uf cap has caused me issues in the past.

Oh i misssed TP10 must be ground... Well there is a tenth of a volt difference in ground potential where ever you where picking up ground.

You need the test rom now to see if it runs at IC17 (or the daughter board? hans?). I would start suspecting the MPU PIA too.

Still think that daughterboard hanging off the cpu slow is not the best solution. The weight of it is going to flex that CPU ic socket.

Most of the time you are going to want to set it to TTL and Pulse. red lead on 5v, black on ground. Green is 0v, red is 5v. Yellow is pulses.

Find the Data buffers at IC9 and IC10. Check the input and output for matching pulses. On these buffers, one side connected to the CPU. p2, 5, 9, 12. The other side is p3, 6, 10, 13. A crashed buffer is a likely cause and a good thing to check with your probe. typically these are gone by the time firepower came out, probably because they caused so much problems. Yours are still installed.

This is going to be much easier to test using a bench top power supply.

http://firepowerpinball.com/downloads/CPULogicDiagram.pdf

Compare each side of the buffer. They should all be consistent on the probe. If you find one data line sounds funky or lights up your probe different it is suspect. A bad buffer leg will be distinctly sounding different than all the rest. The inputs should all sound similar. The outputs all sound similar.

I think Mark's pinball page covers these buffers well. Google mark's pinball and you should find it.

There will be good youtube videos on using your new probe too.