Fixing mid-game Stern Spike reset issue

WARNING SECTION
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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.
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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.

voltage-pot-adjustment (resized).jpg

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:
https://pinside.com/pinball/forum/topic/fixing-led-bulbs-flashers-that-fall-out-of-spotlights#post-4402506

Want to put a quieter fan in your noisy Spike power supply? I made a guide for that, too. It's here:
https://pinside.com/pinball/forum/topic/replacing-stern-spike-noisy-ps-fans

Is your Spike machine occasionally resetting during hectic play, torpedoing your high score runs? This guide to fixing it might be for you:
https://pinside.com/pinball/forum/topic/fixing-stern-reboots-on-spike

Pretty sure the instructions clearly say to use a multimeter with alligator clips to check the baseline at the start and then be able to get the reading in real time to see what you're doing. I expanded the warning section to be VERY CLEAR now, and changed the recommendation to adjust .1v at a time then test instead of .2v at a time and test to address your concern.

It's not common knowledge. I got tired of the "my Spike machine reset mid-game" posts in random Spike game threads all over Pinside, so I made a single thread to address the problem and provide the solution. For all I know, some of these poor sods are shellshocked from GoT Prem and think the resets are "as designed".

As long as you're here, can you confirm that the software for the watchdog circuit has been adjusted to make these momentary-drop resets less frequent, and if that's been adjusted on all Spike software or just some of them? Leaving this important information about potentially safer and easier alternate fixes to the watchdog circuit itself in software that have happened or will happen to rumor and speculation is not super-customer-friendly.

Renamed to something similar to what you recommended.

It's not a switch, it's a potentiometer, which is esssentially an adjustable resistor. I would not recommend you try this fix.

I did the tutorial from memory (I hadn't done it since Ghostbusters) and originally had 48v, then someone was talking about the 5v logic line and I thought maybe I remembered it wrong, so I changed it to that. Today, I went and did a hands-on again with Iron Maiden pro to refresh my memory of the power distribution and adjusted the instructions so they match reality now!

Interesting.

How long since you reset the code? (How many days of play?)
Did you measure the output voltage of the power supply? In attract mode, is is a solid 48v, or a little low like 47.9 or 47.8?

Thanks for following up. That's one more thing to try when people are having reset issues. I hadn't heard of anyone else using this as a solution for that until now. Good to know!

Yeah, it's kind of a bad design for the power - cheap, big Stern surprise.

When you say "randomly resets" do you mean the machine COMPLETELY REBOOTS (black screen, bootup process taking about 30-45 seconds) or you just end up at a new game with 0 score with no reboot process? This is an important difference.

What does the output voltage measure from your power supply (going from the power supply to the power distribution board with the large black caps) when measured with a multimeter?

Here's a drawing from the RSP-500-48 manual. You want the red lead on +V (any of 4-6) and the black lead on the -V(any of 1-3). At rest you should be reading at or fractionally above 48v.

Is this in a very hot environment? This model starts to throttle at 122 degrees internally, starting with 90% power at 122 degrees and decreasing output until 0 at like 158 (off the top of my head). It should run between 95 and about 110 (the fan kicks on at 104).

rsp-500-48 (resized).jpg

If the 48V is fine, or if adjusting it up a smidge doesn't help, you could always secure the leads to the +/- and monitor it live while you play that multiball to see if the extra load drops the output in real time. It may be a defective power supply that only fails under strong load.

Awesome. Stern tech support has done all right with us as well with problems and issues on pins we've bought NIB and 2nd. The only thing we didn't get any replacement for was an Iron Maiden with mild pooling (one of which later chipped). I wasn't super-happy about that, but on balance they're doing okay.