After reading and doing some research about batteries in a pinball game, I decided to investigate mine. I had not changed them since I bought the machine a few years ago and decided it was time. The previous owner shopped the machine prior to sale and sure enough, the 3 batteries were alkaline and two were leaking, not a lot, but enough to warrant immediate removal.

I went to the store and bought a pack of Energizer Ultimate Lithium batteries as seen here: http://www.energizer.com/batteries/performance-lithium/ultimate-lithium/Pages/aa.aspx

From what I've read, removal of the batteries in the pinball machine can be done with the power on. And so I did. I removed the three old alkalines, cleaned the corrosive residue as best as possible, and installed three new lithium ultimates. There is no remote battery holder; it is the stock holder.

I noticed the high score list was reset but nothing else was touched. Volume, free play, etc was all fine. I played about eight games (not once hitting the high score list, mind you) and all is working.

Time to check if the batteries are holding the settings. I turn the machine off, and then back on, and I get "OPEN THE COIN DOOR", which according to the manual, "This indicates that CMOS RAM memory (CPU Loc. U212) has been corrupted. This is caused by either failure in memory (e.g. batteries are dead or faulty RAM) or upon installation of updated version of code. Opening the Coin Door will initiate a Factory Restore, by opening the Memory Protect Switch. Check battery voltage at CMOS RAM with power off."

Factory reset happened as I opened the coin door. Volume was super loud, free play off, but total plays & like audits were not touched. I set the volume, put it on free play, saving the options in the menu prior to closing the door, and let the game restart on its own.

I turned the game off again, and back on, and same thing: "OPEN THE COIN DOOR". Turn it off, reseat the batteries, turn on the game to the same message. Reset the settings, save the settings, turn off the machine, turn it back on, same message.

I do not, however, know how to check the voltage at the CMOS RAM as indicated (i.e. which pins or traces to check). I know the location of the chip as indicated in the manual, but am hesitant to test without some direction.

How likely is it that the memory chip has failed? If it is, why would it fail all of a sudden when changing the batteries?

What do you suspect? Game plays fine without any errors. All LED bulbs on the CPU/sound and power boards are lit as the manual says they should be if in working order.

Any help is great. Thanks.

I believe I have found the problem, but I'm not sure of the nuances of the battery tray.

From the manual, the CPU board has a testing circuit for the batteries. If you test between VBATT on the CPU board (upper right) and GND1 (middle right), you should be able to tell if the batteries are supplying voltage through the RAM. I was reading .04V (machine off, batteries attempting to hold data stored) which seemed awfully low. If I press down on the battery tray so that the left side of the tray touches the PCB, voltage readings jump to .97V, more respectable.

I did not secure the tray to the board with a zip tie because fishing it back behind the board would be near impossible. Apparently, it needs to be. Is this correct? Or, does this signify that the leads off the tray are bad and a new tray put in?

My CPU board is marked 237-1076 Rev D 9/95. Think link shows 237-1076 Rev E but for this test, it's no different. Page 4 shows the points I'm testing. http://www.sternpinball.com/downloads/cpu_sound_bd.pdf

Indeed. This'll be my next big project. There was ~4.7V on that circuit after securing the battery tray to the board with new zip ties. I will remove the board and do some more investigation this weekend.

I've read into the non-volatile RAM and it looks promising, especially being plug/play on certain boards. I'm not a solderer (yet) and so fixes beyond simple repairs are not for me at this time. Starship Troopers doesn't have an external clock that would be affected by the NVRAM correct? There's no log or anything that I can find in the portals menu that seems like it would require the clock to be on all the time.