Tools you may need for minor repairs include - a Philips screwdriver, a straight blade screwdriver, a socket driver (with ¼, 5/16, 3/8 and 7/32 inch sockets), needle nose pliers, a fuse puller and a business card (or similar material).
The bulbs in your pinball machine are going to burn out and need to be replaced. Its easy to miss one burned out bulb, but you will notice the change if you keep a close eye on things. Check out bulb locations while you are cleaning, if one never lights during the game, it needs to be replaced. Its a good idea to have some replacement bulbs on hand. Your manual will list what type of bulbs are used. Anytime you order parts, get some bulbs if you are running low. You usually have to buy ten at a time. Most cost between $.15 and $.60 cents apiece, some can cost $3 or $4 each.
Some bulbs can be replaced from above the playfield and many will only be accessible from below the playfield. If the glass portion of the bulb is above the playfield surface, you will replace it from above the playfield. In most cases that will involve removing the plastic that covers it. Just be careful and remember exactly how it came apart.
The bulbs below the playfield will require the playfield to be lifted and secured. Find the bulb you are looking for and determine how it would be best to remove it. Many are on metal brackets that can be bent back so that you can twist the bulb from the socket. In a few cases you may have to unscrew the bracket that holds the bulb so that you can twist the bulb out of the socket and replace it. Newer machines use circuit boards that have plastic sockets that lock on to the board. Twist the socket to remove it and replace the bulb.
Bulbs are also located behind the backglass. You will need a key to unlock the backglass and be very careful handling the backglass or translite. Sit it in a safe place while you are replacing bulbs.
If you replace a bulb and it still does not work, it could indicate a more serious problem. A game controlled light has circuitry that turns the light on and off. If the replacement bulb does not work and the contacts are clean, it could be a problem with the controlling circuit. Contact your local pinball repair person if you can't get the light to work.
Dirty contacts can also be easily repaired. Lift the playfield and find the troublesome switch. Check the wire running to the switch to make sure they are not broken. Do not file or sand these contacts! If you believe a contact is dirty, rub a business card between the contacts, if the card gets dirty, try another spot until it no longer gets dirty. That should do it. Most contacts are gold plated and just need the dirt removed, sanding would remove the gold and then the contact will fail often and need to be replaced.
Another minor repair is to replace blown fuses. If something just quits working, it may be that a fuse has blown. Fuses are designed to protect the electrical circuits. If the fuse goes bad or some momentary incident caused the fuse to blow, replacing it will get you up and running again. If the new fuse blows as soon as you fire the machine back up, you have something else wrong with the machine and you need to have someone look at it.
Replace the fuse with the type and size indicated in your manual, not with what you replace. Somewhere along the line someone may have just popped a the wrong fuse in just to check something and then forgot to replace it. So find out the correct fuse size and use that. Radio Shack has a lot of different fuses and of course the pinball suppliers can fix you up. You usually have to order at least 5 of each type from suppliers.
Fuses can be found in the backbox, under the playfield or in the cabinet. Your manual should help you locate them. Once you find the fuses, remove them from the holder and inspect them one at a time. Its best to check them with a multi-meter but a visual check will suffice at this point. If they appear blown replace it. If all the fuses look to be OK then further trouble shooting needs to be done by somebody that knows what they are doing.