You can also checkout these (free) test ROMs: http://pincoder.ca Specifically run the RAM and CMOS tests.

I agree with slochar. If the blanking stays low in 01a-leds and remains high under normal game play then it appears to be working. I'm curious though, does the board still fail the beta 02-blanking ROM I put out a few days ago? If so maybe it has to do with fact that the final output of IC7 in a system 4 is essentially inverted from that of system 6. That would change the duty cycle required from PIA1 pin 4 to also be effectively inverted.

Would you mind getting a frequency reading on PIA1 pin 4 while the Williams system 4 ROMs are running? I'm interested to see if it's different than system 6.
I'll then create a 02-blanking to closely match that frequency so that we can see if it produces a PASS on your board.

Thanks!
Craig

Thanks for the pic. I had assumed you were running flash in a system 4 board.

As for the credits/crash you are having, have you tried the 03-cmos and 04-ram-* tests? You'll only need to run 04-RAMIC16 if you have that chip installed.

If the lights stop moving it means the CPU has crashed.

Under normal operation, and under 02-blanking the CPU chip must
regularily tell pia1 to toggle pin4. This output needs to happen
quick enough that it resets the timing circuit before the 556 chip
has a chance to count down to zero.

If the 556 "gets to zero" so to speak it sets the blanking
signal low again. The blanking signal is tied to a bunch of other
circuits..lamps solenoids displays etc and those cicuits are
designed to kill their output if the blanking signal suddenly turns
low.

So what I think you are seeing is the mpu and pia toggle suddenly stops long enough for the 556 to timeout and kill all the lights
etc.

Check the CPU chip and socket for cracked solder joints etc.
Same for pia. You can also try the other tests that have output
like displays and lamps and see how they behave. The interrupts one
is good for testing CPU internals but I think somewhere along the
way the CPU is either crashing or the communication between the CPU
and the pia, or the pia itself, is dying.

I've seen some PIAs that are weak. I they work fine for a bit
but sometime after power up they stop functioning fully. Try a known good pia. New or
perhaps do a swap with one of the others to see if behaviours
change.

Also, you can tell if the CPU is running because the VMA pin
will toggle as it's executing Instructions. The 01b-bus ROM is the
only test ROM where the CPU is purposely put into a wait state and
therefore the VMA signal stays low almost immediately after power
up.

I should also mention that with a questionable blanking circuit you should always keep a finger on the power switch Incase the mpu crashes and the blanking circuit doesn't detect the crash. If that happens your displays will become too bright and possibly burn out. Same thing for lamps. Solenoids may lock on and melt. This is possible with ANY ROMs you have installed. Williams included.

Be careful!

The blink test doesn't use any RAM whatsoever. Perhaps the wiggling is affecting other sockets/pins..

Looks like you're ready for another try

If it only happens when the driver board is connected then something on the driver board is tying up the data bus or address bus, or both, or the driverboard could be pulling down the voltage on the MPU board to an unreasonable level. The driver board also has its own power connector.. check the voltages going into both boards.

Remove any socketed chips on the driver board and run the displays test again.

You could also check the RESET signal voltage. it should be 5V about a second after power up. Check it with and without the driver board attached. If it goes LOW the CPU will go into RESET mode, and basically HALT for as long as that signal is low. If it does go low when you attach the driver board you'll have to find out why. Typically the RESET signal is controlled from the MPU board and nothing on the MPU board should be pulling it low.

You mentioned getting a new CPU. have you tried it?

Also, what's the 'best case' configuration when it does work, and the smallest change to make it "not work"? ie: what's installed on the board etc

What do you mean manually pulled them up?

So I did a little testing on my MPU and driver board. The only time I get all logic highs on the data bus is when the reset signal is low AND the driver board is connected. With the driver board disconnected and reset is low, the data bus is also low.

This would make sense since the pull-up resistors at the 40 pin connector are on the driver board side of the connector and doing their job correctly. I'm not sure why they're even required.

So it seems you have a problem with the MPU chip not having enough current to override the pull-up resistors and actually pull a line low. Since you have tried a different CPU chip and gotten the same results perhaps it comes down to a power supply issue. you may have the correct voltage, but I wonder about having enough current.

I'll try to find some time to see about measuring how much current my MPU is drawing from the power supply.