Calling all EM experts, or anyone with an opinion ... picked up a fairly clean Space Mission last week. Love the gameplay on this one!

Here is my issue. It works 90% of the time, turns on with cabinet power switch - lights on the playfield get lit, then I push the start button, the score reels reset to "0" and then on with a game ...

BUT every 2 out of 10 games or so, it stops at "the playfield is lit up" and it won't do anything else?? It just sits there, mashing the start button changes nothing.

What are the first THREE things you would check in order?

I've done a fair bit of resto work on it so far, cabinet cleaned, new playfield protector, new pop caps, new leg bolts, new rubbers, repaired plunger rod, rebuilt both flippers, filed/stoned the switch contacts on the flippers/EOS switches, replaced lane guides, fixed horseshoe advance button, ordered new plastics, etc. etc.

I also have a digital copy of the schematic from IPDB and can print if needed

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Thanks for both replies guys. The reset cycle will be helpful and ...

No - the score reels during these times are not resetting to zero - they are not "trying" even

There are occasions where the reels don't fully reset to zero, but they "try" and sometimes leave a score up, but the game starts anyway

Hope that helps to narrow it down some ...

Thanks for sharing that animation. Super easy to understand once you watch it a few times. (runs fast!)
I'll check them today

Yes sir! Thanks so much ... when I manually pull in the reset relay, score reels reset to zero and game starts as normal.

Here are some pics of the reset relay before pulling it in manually. Seems like one of these switches is maladjusted or maybe reset relay is not getting signal from start button?

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Thanks for all of this. Hate to seem dense but EMs are rather new to me ... couple questions:

I think I know where "some" of these switches are (credit switch and reset relay as examples) because I "know" where the credit button is and can easily see the switch. I see the reset relay right behind the transformer because it's labeled or I wouldn't know what it was!

How do I "find" the other switches?
What am I checking? Normally open vs closed and vice versa?
Continuity? Voltage?

Probably all the above!

Thanks for any help

BTW, I checked all the reel switches and compared to animation. All look good at zero

Hugely helpful on all - thanks so much. Will get busy later today sniffing this all out!

OK - made some progress thanks to you all. I've got the manual and schematics printed
Checked the switches that I could find and all appeared normal. Game Over re, Reset re, Credit button sw, Index switch "A" on motor stack and a few others.

Cleaned them while in there but all appeared to be in correct NO/NC positions

Here is where I made progress:

See below pics of coin door switches. One has 3 blades, one has 2 blades - why are they different?
If I push in on the back blade (toward head of machine) on the switch closest to the lock, I can add credits to the machine AND simply push the credit/start button to start a normal game. If I make contact using the 2 blades on that same switch that are closest to the face of the coin door - nothing happens
If I drop a coin in the coin chute ... it drops thru, hits the thin wire but does not add a credit like pushing in that 3rd blade does
I'm fine using coins to start the game but how would I get a coin to create contact with that "3rd blade"?
That blade does not seem long enough to be physically moved by the nylon "cog"?

Now, on to the other coin door coin activated switch ... the one with just 2 blades. I can make contact there but no credits are added

How was I playing this previously without "credits"?
Did the prior owner simply have the max credits stacked up on the credit mech - then I "ran out"? (seems unlikely)
Also, when I make contact using that "3rd blade" on the coin door coin activated switch, the max credits it will let me add are 18 total. If I continue to push that blade to make contact, the credit indicator does not advance

Lastly - see the video and let me know if the coin door solenoid should be activating during gameplay. Seems odd but to be honest, I have no idea what that coil does in the game anyway!?

Thanks in advance for the help!

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Think you are spot on ... I used info from pinrepair.com to jumper .. and as you said and it works perfectly

I ALSO took just a few minutes to better understand how coin mech switches work and got them both working again - that third blade was waaaay too far bent back and is supposed to be a normally closed blade that is opened as the coin drops thru (see slow mo video)

The first pic is of the now properly adjusted coin mech switch
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This pic is where I jumpered the switch to set game always on free play
Got image from here http://www.pinrepair.com/em/index3.htm#free
... and same recommendation from Cheddar (thank you sir!)
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Shot a slow mo video of it for any other for future reference