I had resetting issues with my Bally Skateball. It usually occurred when the flippers were activated. In the Skateball, there are 4 flippers, and leaf switches on the bottom two flippers close when the bottom flippers are up, and this then provides the power for the upper flippers. I noticed on mine that these switches needed adjusting, as the upper flippers would flicker due to the lower leaf switches not "contacting well" when the lower flippers were activated. After adjusting these leaf switches, no more reset problems.
In your case you do not have this situation, but I believe what happened in my case, and may happening in yours, is some power surge. Does the reset occur when a solenoid has just been activated, or is it at any time? There are other reset triggers - the Alltek boards desire a very smooth 5.0V, and the capacitor C23 (on the SD board) needs to have low AC (less than 250mV) on it. My Skateball's C23 is hovering around 200mV, and I should replace it.
There's also the coil diodes to check (this may be worth it if it is resetting during solenoid action).
Have a read in the section "Game Reset or Lockup Power Problems" in this link
http://www.pinrepair.com/bally/index3.htm#reset .... quite a few things to look for.
