I picked up a non-working Granny and the Gators about a month ago and have been looking at it and trying to get it working since then. The game will not boot, when it turns on the game starts its self-tests and seems to complete them but shortly after the last flash on the vidiot deluxe board, there's a "click" that sounds like it comes from the boxed relay on the drive board and the LEDs on the idiot board and cheap squeak go off. There is a brief image that flashes on the display when this happens and then it goes blank (but appears to be on still, you can see the square backlight if I turn the lights down in my workshop) but no fuses are blowing so I don't believe it's something to do with the game shorting out... just not sure what exactly is going wrong. Here's what I've done so far:

When I first got it, the MPU looked pretty beat up and the battery connectors were gone. I ordered the Alltek Ultimate replacement board and installed that with the dis-switches all set properly for Granny and the Gators. This didn't solve the problem.

I noticed corrosion on the TMS9928 processors and the RAM at U29-U36 on the Vidiot Deluxe board, and since the video display isn't showing anything I was suspect of the video board. I replaced both processors and the RAM at U29-U36, but this did not solve the problem either.

I haven't been able to track down exactly where the "click" happens when the boot process stops, but it sounds like it might be on the boxed relay on the driver board. I'm not familiar with or able to track down any information on how that relay functions (feel free to point me in the right direction if you know!) so I'm unsure of how to test that or what it means if that is happening.

I'm hoping somebody with familiarity with this game could give me some suggestions on what to test to further to narrow down the issue and what's going wrong? I'm thinking of replacing the solenoid/driver board since there is also an Alltek replacement for that but since replacing the MPU didn't necessarily "help" anything, I'm hesitant to do that without reason? The solenoid/driver board is in better shape than the MPU was and I don't see any visible corrosion or places where it looks like it's gotten hot or damaged.

Thanks in advance for any help/pointer you can offer!

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Thanks for the info, I think you've gotten me closer to figuring out what's going on. The MPU does flash 6 times, I think there are 7 flashes in total per the manual, and you're right, the last one is for zero cross detection. I checked the 43v at the test point on the power/rectifier board and it's good there, but it's missing on the 43VDC test point on the MPU.

Sorry for the delayed response, after you pointed me in the right direction I kept trying to poke around but I'm unsure of where exactly the issue could be or what to check next. That 43VDC is the coil power to the playfield right? Do I need to look for a short somewhere along the line from that 43VDC from the power/rectifier board, to the playfield, and then back to the MPU? Thanks for your advice so far, any other tips you have for where I should check next would be great, otherwise I'll just keep trying to figure it out and make sense of the schematics and machine in front of me.

I did check the MPU dipswitch 16 and it's set to "off" currently, but that's what it's listed as correct, although there is no further information on what the dipswitch does.

Just wanted to follow-up on this post with what I finally figured out in case anyone runs into the same issue and finds this in the forums.

So I was correct that the MPU was failing at the zero-crossing check. I looked at the schematic and found there's a test point on the MPU for the zero crossing voltage, and I also found the pin where the voltage comes in. When I checked it the voltage was 0VAC... 18vdc? I believe the test point is supposed to be around 5VAC and the pin itself should have about 6.7. The voltage for the zero crossing is the Phase B power line that also powers half the switched lamps. I checked the voltage from the transformer, two purple leads that don't go through the rectifier board. 0VAC across the wires and 18vdc on one, 3.3 vdc on the other.

After learning a bit about how that phase A/phase B switched lamp circuit works on this Bally system, it seems like the root issue is that one of the secondary windings on the transformer isn't working correctly. It looks me awhile to track down exactly what voltage it was supposed to be, but I ended up determining that the secondary needed to be 22VCT, the CT part being important because it means it's a center-tapped transformer, the result being that measuring across the two leads gives you 22VAC, measuring either lead to ground gives you about 11VAC, each leg is out of phase with the other so when one sine wave is +11v the other is -11v. The reason they did this is so that 1 SCR on the driver board can control 2 lamps. (If any of this seems incorrect to you wiser folks out there, feel free to chime in with your thoughts.. I was learning as I went and am only assuming I was right because it worked when I was done).

I found a new transformer to replace JUST the secondary that wasn't working on the original transformer, it's a Hammond 165V22 transformer. I spliced the primary leads for the new transformer into the same power lines the original transformer uses too so it turns off and on with the cabinet switch. After splicing the secondary leads in I fired up the game and... it works! Boot right up and plays in both video and pinball modes. There's still some color weirdness I'll need to fix by replacing the pots on the Vidiot Deluxe board (they're 40 years old, sweeping the pot doesn't change the color but even the slightest bump or wiggle turning them produces a lot of distortion on the screen).

I hope this info is helpful to someone else someday, this was definitely my most difficult troubleshooting I've done on a pinball machine so far but I enjoyed figuring it out.

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