When I got it, Target Alpha had 2 score reel problems: the 3rd player thousands carryover bit was tied to the ten thousands, meaning that when the thousand score reel advanced due to the hundreds carrying over from 900 to 1000, then 10000 score reel also advanced.
And on player 4, the ten thousands just never advanced.
Player 1 started being unable to rest the hundreds reel. You could see it struggling, but never had the coil strength to advance.
So this one is the most straight forward: Game is all at zeroes, but there is this undreds reel stuck at 7. Open up the back, all of the contacts are open except the middle ones. Obviously these have gotten dirty. A quick cleaning and they have the proper contact to advance the reel.
Looking from the back, the first set of switches is closed on zero. The second switches are 1-9. And the third is the carry bit, which is set on at 9 and means the current reel advances, as well as the next in line.
This carry bit will be where our carry problems arise in players 3 and 4.
So let's say we have a reel with 9000 points on it. Here are 2 scenarios:
Problem: 10,000 point reel is not advancing when we score 1000 points.
Solution: on the 1000 reel the rightmost (carry bit) switch is not making good contact when at 9000.
Problem: 10,000 point reel is advancing multiple times!
Solution: the rightmost (carry) switch is most likely sticky. When at 9000 and then you hit a 5000 rollover, the 1000s reel will click up 5 times. After it moves past 9 the rightmost (carry) switch should separate, but if at all sticky, more than one of those pulses could carry through and advance it.
Another random issue was that a 10s reel wasn't resetting to zero properly. Cleaned the left-most (zero-position switches) and that fixed the issue.
The reel itself can slide out if you gently push aside the plastic latch at the bottom. I've never actually taken one all the way apart, but it is useful to just slide them back a tad to make working on them easier.
On the left side there is a plastic protrusion which you can pull towards you to manually advance the reel, simulating the solenoid. I wish I knew about this before, as it makes checking and adjusting the switches much easier.
There is also a plastic piece on the left you can push in that opens the switch stack, making it easier to clean the heads when in zero position.