How to buy an arcade machine (cabinet)
This guide is organized into two sections. The first section describes what I consider “must haves” and other critical information/decision you will need. The second section contains “nice to haves”, things that I consider desirable, but not critical.
Will it fit in your house? Ask the seller for precise measurements. Leave at least five centimetres on either side for maneuvering the beast. Measure your own staircase, if it's going down or up a flight of stairs.
Does it work properly? If you happen to be within a manageable distance to the seller, pay a visit and ask to see it work. Keep it running for as long as possible while you're there to possibly identify overheating, unstable power, or anything else that may cause it to restart, shut off, or malfunction in any visible way. These things are tens of years old and do break down.
Make sure you check all buttons, or as many as you can, given the game in the cabinet. Try the second player buttons as well, and also the P1 and P2 start. Try to perform special moves with the joystick. Be a little rougher than usual with them. Unless you are a handy person who's familiar with repairing electronics, stay away from “almost working” machines.
Check the speaker(s). Research the type of arcade motherboard it has inside and see if it outputs mono or stereo sound. Leave the game in attract mode and listen carefully to the sound effects. Then start playing and listen to the music. Don't buy if you don't think you're fully satisfied with the sound.
Find at least one more person to help you transport it. My experience has been with a machine that was six feet tall and weighed about 350lbs. You'll need a truck, or cargo van. Buy some cheap tarp (find it at dollar stores) so that the machine slides easier onto the truck's bed. Buy a cheap utility blanket, and bring some cut-up cardboard pieces to place underneath the machine so it doesn't get damaged during the trip. I suggest getting two more people to help you carry it, especially if it's going upstairs or in the basement.
Obtain wife approval.
Ask the seller to show you how to adjust the monitor. These controls can modify how the image looks, colours, saturation, white balance, etc. Experiment with the colour/contrast settings. They will usually tell you if the monitor's in good condition if you can make the picture vary greatly. If it's always looking washed-out no matter what you do, you may have to live with it.
Check the monitor for burn-in. While it's not a deal breaker, I sure hate seeing traces of other games' title screens on top of my monitor.
Verify the coin chutes. Even when the game is in free play mode, the machine should still register coins. Try both chutes and listen for the sound! Ask the seller for the keys to (usually) both doors - the coin chute door and the coin drop box door.
Find out how to open the cabinet to reach the motherboard and/or games. On a multi-game system such as Neogeo MVS, try to change a cartridge yourself to gauge if it's easy enough. Research online the compatibility of your harness (the connector that hooks up the game to the controls, monitor, speakers, coin chutes).
Research the motherboard. Research what games it can run, and how much they cost. My personal favourites are Neogeo MVS and JAMMA type boards.
Many collectors consider the decorations on the cabinet to be extremely important. I'm not one of them. But you should think about whether you'd like your arcade machine to have its original decorations, or whether you'd settle for a restored one as well. Look around the cabinet - sides, bottom front, and control panels. If you notice that one looks or feels unlike the others, it's probably been restored.
Is the board configurable via DIP switches? Ask for a manual, or try to download one in advance. Try to move the game between regular and free play. I don't think it's a big deal if you can't get the DIP switches to work, because the default settings are usually acceptable. And if you do have to put quarters in, you will have the key and be able to retrieve them, anyway!
Have fun buying your first arcade machine. It's a very satisfying experience.