Does the second player start coincide with the ball being sent into the shooter lane? If so, this really seems to be some kind of weird System 6/6A issue. This is at least the third post I've seen about the issue, one that I have myself with a Blackout, and another has it with an Alien Poker. I've mostly ignored it and just played the two player game when it happens. I know, that doesn't help. I've looked at the schematics and haven't seen any obvious common element that could cause it.

Here's another example:

https://pinside.com/pinball/forum/topic/alien-poker-oddity

Our Gorgar did this, Time Warp, Scorpion, and a couple other system 6s have done this. We have checked and changed and rechecked switches, diodes, connectors etc. it will go away for awhile and then just do it again...as Neurkinetik said I think it is just a system 6 thing. No reason that we have ever found, just a glitch in some system 6s and 6As. We have some system 6s and 6As that have never done it. It seems to be just a system 6 or 6A thing no system 7s we have had have ever had this issue...

Phoebe

If the boards are not the issue, then the first thing I'd look at is grounding, and/or power supply.

I'm 100 games in, I think you solved it, well done.
-mof

My gorgar does this and a friends flash does this. Can you guys confirm the issue still Hasn't come back? mof Jabbles180

Sounds more like the start switch isn't debounced in the code so occasionally it will register as two presses instead of one.

Had TWO blackouts that did this exact same thing. Never did find the cause.

Interesting my Stellar Wars does this every once in a while and mine happens to be one with system 6 board set.

My Gorgar is at a friend's house permanently, so I have no idea about weird behavior like that, afaik it went away.
-mof

Agree, dirty start switch contacts and poor or non-existent de-bounce code.

Clean the contacts by pulling paper through while gently pressing the contacts together. Then gap the contacts close together and tight against the start switch plunger. Works every time.

Cleaned the contact. Works perfect now. No double starts anymore! Thanks.

Ensure there is a ground lug on your power cord. Missing this causes two player starts.

This is actually the correct answer. It was always a problem from day 1 with these games - the way the williams switch matrix works in system 6 is the same way the bally/stern switch matrix is read for the fast react switches (slings and pops) - when it sees 2 closures in a row, it adds the switch to a queue. ("normal" switches on bally/stern need 3 in a row to be valid, and only activate once until it sees the switch open... this is why you can't add a switch matrix capacitor to williams switches to improve response, it will just keep scoring after the first activation).

Boardsets, dirty switches, diodes on coils, etc. are all red herrings. Yes, it will work correctly for a while, but eventually, it will come back, because leaf switches bounce. Someone with a heavy hand on the start button will get this a lot, one start on the push in, one start on the pull out.

The correct way to get this fixed is to add a small routine in the gamerom to the credit switch that turns off switch scanning for a short time - they already do this for some other switches on the PF (the outhole, and usually drop target switches on the reset stroke) - they could have added it to the credit switch easily. Probably didn't come up in their testing though.

Good software design takes into account [natural] deficiencies in hardware.

In this case you can minimize the double hits by widening the gap in the switch as much as you can, but it will still happen occasionally.

Oddly, in most cases when you are setting options in the adjustments you will NOT overshoot as you'd expect with the switch double hitting, because it is properly debounced in software in that case - there is a built in delay everytime you press/hold the button, and it reads it differently - it polls the closure instead of just reacting to a queue. It's not practical to scan an entire switch matrix that way though, it would be too slow.

For anyone who wants to really get to the root of this problem you can use the "bounce" test ROM in this package: http://pincoder.ca

It will easily show you if any of your switches are in fact double bouncing. I wrote this ROM because I have exactly the same issue with my gorgar. and yes, it's occasional.

When I run the bounce test on mine, the switches register exactly as they should, so for my gorgar, the boards are fine, as are the switches and wiring. I can only assume the problem is in how Williams wrote the GREEN ROMs.

Having said that, if you run the bounce test ROM and it shows actual bouncing on any switch then you should start with the switches and make sure they have the correct gap etc. Then look at wiring. If all is well there then the problem is likely a bad PIA chip. The documentation for the each of the test ROMS will help you find the problem.

There are many other valuable test ROMs you can use to check the rest of your machine. Download a copy and take a look at the docs for each test. They're very easy to use!

Seems to be an issue on System 6 games with green flipper ROMS. Have fixed a couple by replacing the paper between the contacts on start switch.

My gorgar did this but i just cleaned the contact on the start button with isopropyl alcohol. Now i never get double starts unless the start button is actually pressed twice.

My alien poker does this as well. Ill be trying the start button cleaning method as well.