So I have an M-200 MPU in my Star Gazer that doesn't always reset/boot reliably when I power the game on.

It works fine about 2/3rds of the time. When it fails the MPU has a solid LED. Pretty sure it's not resetting consistently.

I power up my games with a wall switch that turns on the plug circuits. Often Star Gazer won't reset when the wall switch is turned on and I'll have to use the cabinet switch to power it off and on again. It almost always boots fine when I do this.

I completely rebuilt the reset section on this board after repairing alkaline damage on it a few years ago, so every component is newish.

I also saw a tip on http://techniek.flipperwinkel.nl/ballyss/rep/index2.htm#flash to use a capacitor to make flaky reset circuits more reliable:

"It could be the +5 volts is not stablizing within the "window" the CPU expects (about 50ms). To make the reset window longer, try putting a 470 mfd electrolytic capactor in the reset section (on the solder side of the MPU board). Solder the positive leg of this cap to the collector (top leg) of Q1. Then solder the negative leg of the cap to ground (the emitter of Q1). This will increase the reset timing length. Now test the MPU board. If the MPU board works and continues with the flashes, the +5 volts was just not getting "stable" in the 50ms window (there could be a power supply problem, probably with the large 5 volt rectifying capacitor on the driver board). "

I tried adding a 470uf cap as described but it made it worse. In fact it only booted once in about 10 tries with the cap installed. So I removed the cap and now I'm back to it booting about 2/3rds of the time with the wall switch.

Oh, the powerboard is using one of those new fangled solid-state voltage regulators also (voltages are fine once things are booted).

Any thoughts or suggestions?

Yes, on the SDB.

TP1 = 4.79vdc
TP3 = 4.65vdc

I also noticed that I replace R50 with a jumper wire. Been awhile so I don't recall the reasoning, maybe related to using the EzSBC.com PsU5 voltage regulator?

Tried this, no improvement.

I don't, but I do have some other working Bally SDBs that I could potentially swap in to this game. Worth it?

Okay, so I swapped the SDB from my Flash Gordon. Problem gone. Interestingly, the problem doesn't occur on Flash Gordon either, even with the EzSBC.com PsU5 voltage regulator.

I won't keep it this way though, I like my games to have the original Stern or Bally boards in them.

I guess I could try swapping just the voltage regulators between the boards, a bit of work though. At least I know it's probably not the MPU board at all. I can live with re-booting the game manually once in a while.

I either didn't realize that was there or had forgotten about it since installing it.

So I adjusted it while it was installed in Flash Gordon to be an even 5.02vdc on the SDB. Then I moved the SDB back over to Star Gazer and it booted fine.

Here's where we enter "couldn't just leave well enough alone" territory...

So I figured I'd check to see if it could use any further adjustment on Star Gazer, and sure enough it was reading 4.85vdc on the SDB. So I adjust the pot up a bit and booted the game. Alternating solid red LED or flicker with no flashes on the MPU, and a fairly horrible static sound coming out of the speakers. Multiple reboot attempts, same thing. Solid red and single flash seem to alternate with power cycle attempts. Ah crud.

So not exactly sure what happened but it seems like I either under or over voltaged my MPU board with that last adjustment, or maybe all the power cycling damaged something.

So my voltages now are:
SDB: 5.15vdc
MPU: 5.05vdc / 13.88vdc.

Since I was getting a flicker but no flashes I replaced the 4 ROM chips with an older set that I had and it will now boot to 2 flashes. 5101 memory must have also taken a hit. I installed a couple spares I had but same thing, 2 flashes.

So it's roughly alternating between solid red and booting to 2 flashes now.

I guess sometimes best is the enemy of good-enough.

So in the process of removing the bottom 5101 chip one of the socket pins came up with it. *sigh*. I had replaced this socket already and had to patch a few of the traces in the area due to the alkaline damage. Removing the socket again destroyed a few more traces. Initial attempt to repair failed, it's looking pretty dodgy in terms of my ability to repair this.

However, I have a "spare" MPU-200 board that I pulled from a Big Game about 18 months ago due some strange reset and controlled lamp flickering issues. I have modified the jumpers on it for my Star Gazer roms and it is booting! Still has the exact issues that it was exhibiting in Big Game though. Moving that discussion to it's original thread: https://pinside.com/pinball/forum/topic/big-game-mpu-200-issues

This is really good to know. Unfortunately, in this case I decided to salvage my board for parts and used some of them to get another MPU-200 board I had that was in overall much cleaner condition working.