You need to adjust the zero position switch. Check here for more info and pix: http://www.pinrepair.com/em/index1.htm#lube

currieddog may be right. Here's a piece of a schematic from another Gottlieb single player. Your wire colors and relay names will probably be different, but the control logic should be similar.
100s unit reset (resized).jpg
During reset the score motor turns, and the Motor 1A switch in the lower right sends 5 pulses per 120 degrees of score motor rotation into the score reel reset circuit along path shown in red. From the Motor 1A switch the pulses fan out into a circuit for each score reel. The path for the 100s score reel goes through a switch on the A relay, then through the runout switch on the score reel before reaching the 100s score reel solenoid.

Since your other score reels do reset the Motor 1A switch is doing its job but something is preventing the pulses from getting to the 100s score reel solenoid. Assuming a wire hasn't fallen off its solder tab or something like that, the pulse is getting dropped in either the score reel runout switch or in the 100s score reel switch on the A relay.

The A relay is an interlock relay (with two coils). An interlock relay mechanically holds the switches in the position of the last relay to fire. So even though the A relay fires only momentarily, the switches in the relay will stay in the "A fired last" position until the "A Reset" coil fires. The A relay fires at the start of a new game to reset the game, and "A Reset" relay (in this schematic anyway) fires once the reset sequence is complete.

At the bottom of the schematic above you can see why the motor keeps running. The "A Reset" relay can't fire until all of the score reels have reset. Once all four score reels have reset and their series switches close, the "A Reset" relay will fire at the end of the score motor's 120 degree rotation indicating that reset has completed. Note that the schematic shows all four score reel reset switches leading to the "A Reset" relay are already closed. That's because the schematic shows the state of the game after reset has completed. At the end of a game, most of the score reels will not be at zero so most of those switches will be open.

/Mark

Thanks.

So if I understand correctly, you adjusted something (what was it?) so that all the score reels now reset to zero at the start of a new game. But during the game, both the 10s and 100s score reels advance when 10 points score except when the 100s reel is at zero. Is that right?

What happens if the 10s score reel is at zero, and you score 10 points? Does the 100s score reel advance too, or just the 10s score reel?

If you look at the schematic above, you'll see that each score reel solenoid has two circuit paths leading to it. The lower of the two paths (through a "Runout" switch) is the reset circuit. It's only used when a new game is started and advances the score reel to zero but no further. The upper path (through an L, M or N switch) is the scoring or increment circuit used during the game.

If your 100s score reel advances when 10 points score but only if zero isn't showing, that sounds like there's a short somewhere that's letting the pulse get from the 10s score reel increment circuit to the 100s score reel reset circuit. It could be happening in the switch stack of the A (reset interlock) relay since both the 10s and 100s score reel paths go through that relay. Do all the switches on the A relay open and close as they should when the interlock relay opens and closes?

The short circuit path causing the problem could be from the 10s score reel increment path, out through the 10s score reel Runout switch to the A relay, shorting through the switch stack somehow, then through the 100s score reel Runout switch to the 100s score reel. The path goes backwards (left to right) for a while on the schematic, but the electric current wouldn't care - it just follows the closed circuit.

If this theory is right, you should see the 100s score reel advance whenever the 10s score reel advances except when either the 100s or 10s score reel is showing zero. When either one shows zero, its Runout switch opens which prevents the pulse from getting through that short circuit path.

Are the screws that hold the switches on tight?

Can you elaborate? What happens starting with the last ball about to drain? Does the score motor turn? Does the M relay (or whatever relay drives the 100s score reel) fire? What else fires or moves?

This might be trickier to diagnose without a schematic.

Sounds like the carry over is kicking in when it shouldn't. On the 10s reel, there is a switch that will engage when the reel is at 9. So when the ten reel is at 9, and is advanced, the switch will cause the hundreds reel to be engaged as well. (so Tens goes to 0, and hundreds is advanced)

I think they call it the 'runout' switch in gottlieb schematics? Basically, look at the switch that changes when the reel is at 9, and make sure its on/off accurately and not accidentally triggering.

Is it the same problem you described in reply #4 above? Is there a carryover to the 100s all the time or only when neither 100s or 10s is at zero?

Does the 100 Point relay activate when it's giving the extra 100 points?

If you put 100 points on the score reels and hit a 10 point target twice, do you go from 100 -> 210 -> 320, or from 100 -> 110 -> 220? In the first case the 100s score reel follows the 10s score reel both times and something else may be going on. In the second case the 100s score reel follows the 10s score reel when the 10s reel is not at zero. That would support the short circuit in the reset path theory described in reply #5.

BTW if you scan and post the section of your schematic that covers the score reels like the one above we can help you with wire colors, relay names, etc.

The score motor will pulse the 100units coil if the 100units runout is improperly closed. Otherwise, it will only fire if the switch in the 100units relay is closed. That makes it pretty easy to narrow down which switch isn't opening fully. Start by seeing if the 100s relay is closing when you get these improper scores... then you can either look at what's triggering the relay, or focus purely on the runout switch.

Look at your schematic, and look at the Add Hundreds Unit coil (11-D area on schematic). Then simply work your way back to see what switch states allow that coil to fire.

This sounds like a problem in the switch stack on the reel. There are three different configurations of the switches -- 0, 1-8, and 9. Sounds like, when stepping from 0-1, the 9 / runout switch is closing (and staying closed through 1-9) -- but it shouldn't close until you get to 9. With that switch closed prematurely, every time it advances from 1-9, it's pulsing the next reel to roll over.

Reference the info & pics here: http://www.pinwiki.com/wiki/index.php?title=EM_Repair#Score_Reel_Switch_States