Working on a system 4 mpu for a friend. when i put it on my factory test fixture (with test rom) all the controlled solenoids pull in (but does boot and go into test mode, I did get 55 55 on the match/credit display once but I haven't been able to replicate it). I put my system 6 mpu that I use for the fixture, all the solenoids are off and test good going through the test prompts. I have reset and blanking on the system 4 mpu, what am I missing? all rom sockets have been replaced, and the 40 pin interconnect also. I had him bring me his solenoid driver board and found a bad pia for the solenoids and replaced that, the pia sockets, and also the 40 pin interconnect. I tested it with my system 6 mpu and it works perfect. so it is something definitely on the mpu causing the solenoids to pull in. also the system 4 mpu was tested and working 100% on my fixture before I sent it off to him the 1st time, I don't know if the bad pia on the driver board messed something up on the mpu.

Edit:

Added a led blanking mod to my driver board that I use on my factory test fixture. Check photos below.

It's on my williams factory test fixture so no fuses will blow. But the solenoids light up the second it boots. So you get the 2 flashes on the mpu and then all the solenoids come on.

I'll have to check the blanking again then, I might have missed something.

Blanking was fine, ended up being a flaky pia on the driver board. I dunno why it worked fine with my sys 6 mpu but not the 4. I first moved it and the problem followed the chip. So I replaced the pia and all is good. Funny thing is it tests good on the neoloch tested. I might send this chip to him so he can maybe figure out why it passed in the tester but is still bad. I have a bad pia I keep as a control and it still tests bad so this is an odd one. For the record it was a Motorola brand pia, not an ami that do weird things.

I would like to add this. I added 2 led's and 2 150ohm resistors to the blanking input on my driver board that I use on my test fixture. This is super simple, credit to pinwiki for showing how to get the blanking high signal with an led. I reversed another led since 5v logic power is available right by pin 37 on the header this was super easy. Here is a pic. The resistors are added to the anode of the led (does not really matter but I used the anode so I knew which was the anode and the cathode)

Pin 37 can be found at the top of R195

For blanking high I put the anode to pin 37 on the driver and scratched a spot on the ground plane to attach the cathode.

For blanking low I put the cathode to pin 37 and put the anode on the 5v line located at the bottom of the resistor R191

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This is blanking low.

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This is blanking high. I used red and green like they would be used on my logic probe so I wouldn't confuse them.

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