DO THIS FIX AT YOUR OWN RISK. IF ADDING A SINGLE MOD CAN KILL YOUR SPIKE MACHINE BECAUSE THE POWER BUDGET IS SO TIGHT AS GOMEZ SAYS, THEN YOU CAN DEFINITELY SCREW UP YOUR MACHINE IF YOU DON'T HEED THE WARNINGS IN THESE INSTRUCTIONS.
If you aren't comfortable or capable of working in or around a live power-supply, DON'T DO THIS. You can get shocked if you do dumb things like stick metal tools into the power supply leads. And if you adjust, DO IT IN SMALL INCREMENTS, then test for a while. DO NOT EXCEED 48.5v!
This tutorial was adjusted because you can't adjust the 5v line directly, so you have to bump up the 48v going out of the power supply a bit, which should in turn prevent the 5v logic line from dropping low when the power supply is under load.
Spike machines have a watchdog circuit that will cause the machine to reboot if the voltage drops below a certain level. It can affect all Spike machines through at least BM'66, maybe all of them. It usually happens when you're in a mode with a lot of action (lots of balls, coil hits, flashers, etc) that put too much load on the power supply output and cause it to drop momentarily low, which triggers the watchdog and resets the machine. You can fix this by bumping up the output from the power supply a bit (most tolerances are +/- 10%, but we won't be anywhere near that, I would stop at 48.5v max - 1% over spec). The watchdog circuit is on the 5v line, and that is split out from the 48v the CPU board is supplied, so to affect that 5v, you need to bump up the 48v output from the power supply.
There is a potentiometer at the bottom of the power supply (see picture) you turn VERY SLIGHTLY clockwise with a plastic tool to increase the power output. It's best to get a baseline with a multimeter, then use alligator clips so you can watch the output as you turn the potentiometer to get it where you want it. It will not take much to stop it from dipping low under load - much less than half a volt. It's recommend only bumping it a tenth of a volt and see if that fixes your problem. If not, do another 0.1v increase and test again. It shouldn't take much to keep it stable even under load. Again, max of 48.5v, and that should stop your machine from dropping too low under load and resetting.
Supposedly Stern has adjusted this watchdog circuit with software updates, but resets are still happening, so I don't know if it's not updated on all machines or if the software fix doesn't work well. The above change should help stop your resets.
(I just checked Iron Maiden Pro and it was at 47.8v from the factory, so I bumped it up to an even 48v from the power supply)
All done with this project? Here's a couple other guides I've made for newer Spike machines:
Are LED lights popping out of your spotlights (Not just Spike!)? Make sure they never fall out again:
Want to put a quieter fan in your noisy Spike power supply? I made a guide for that, too. It's here:
Is your Spike machine occasionally resetting during hectic play, torpedoing your high score runs? This guide to fixing it might be for you: