In order to clean dirt and spills, as well as to repair misfiring panels and replace broken sensors, you will need to disassemble the front panel. This is probably one of the worst games to disassemble in terms of how complicated it is to get to the serviceable parts.
First, you will want to unscrew and remove the decorative side panels. There should be two screws on the front of the cab on each side, two on back on each side, and two near the control panel on each side. This shows the screw location for the right side panel control panel screws:
Once you have both of these panels off, you will want to remove the front decorative panel and the decorative panel in the center of the screen. Both should have two screws:
Now that the decorative panels are off, you should have access to the wiring underneath. You can unplug the wires from the four connectors now. Note that you can do this with the cabinet running. I do so with the test screen up so I can reattach and test repairs before fully reassembling. Once the connectors have been unplugged (four on each side), three screws on the top and three screws on the bottom of the assembly hold it in. Unscrew them:
You should be able to remove the whole assembly at this point. Flip it over. If there is a protective rubber cover, remove it at this point. You should have a panel that looks similar to the following:
Now that you have access to this, the first thing you need to remove is the center brace. This secures the center part of each of the 8 sensor boards. Remove the three nuts that hold it down. Now is a good time to remove the other nuts holding down various parts of the circuit board. Do not remove the two nuts on the very top and two nuts on the very bottom of the assembly. These hold the front decorative plate to the back, and if you remove them all of the panels and rubbers will fall out everywhere and you will be so sad. Your panel should look like this now:
Removing each sensor board is as simple as removing the four screws that hold it. A detail of one sensor board with the four screws that hold it is shown below. Note that if you are trying to repair a single panel, you only need to remove the circuit that covers it and its neighbor.
Once you remove the circuit board, the rubbers that make contact with the PCB will be exposed. Make sure that none of them are broken or dirty. Sometimes the actual plunger piece can get torn off and fall into the cabinet or get bent. Replace these rubbers with new ones if this happens. Failing to do so can cause a misfiring or sticking panel.
At this point, you can clean the PCBs and rubbers in order to prolong their life and replace any that have broken. Note that if you are cleaning the rubbers themselves, do not
use alcohol. This dries out the carbon contact and causes brittleness. Simply use warm water on a q-tip to swab them clean. On the PCB, you can clean with a q-tip and alcohol. If you have a particularly nasty stain or lots of dirt build-up, you can use a pink erasor as an abrasive with rubbing alcohol as the solvent to shine up the contacts before making one last past with a q-tip and alcohol.
When you re-assemble, pay no attention to the order in which you put on the PCBs. They are interchangeable, and the wires can only reach to the correct location for the panel. If you put the sides back on backwards the screws that normally go to the control panel will be at the bottom. Just reverse the panels and you are good to go. You can test on the go by partially re-assembling and plugging in the wires to check your work.