The Mouse

An alternative to repairing your mouse
If you are having problems with your mouse that are more than just needing a cleaning you might consider an inexpensive mouse replacement that is available from many mail order companies like MacWarehouse. The MacPoint mouse (catalog cost $29.95) is very inexpensive for a mouse. I have tried it and it works very nicely. When I took it apart I was impressed with it's construction. I like the feel of it too because it feels more like the older ADB mice Apple bundled with it's Macs before they lightened them up with newer Mac models.

Mouse Basics
unlike most other computers the mouse is a very necessary window into the Macintosh computer. Long before a mouse was used for anything more than a specialized input device in drafting rooms on other computer platforms, Apple had made the mouse the input device for the Macintosh.
The mouse is an electrormechanical device. Small rubber rollers are turned by the rolling ball. these little rollers are connected to a small wheel with slots. The slotted wheels rotate and interrupt light from a diode creating a strobe effect. The computer counts the speed of the flickering light from the wheel and uses this to calculate the mouse speed. From this it keeps track of pointer location on the screen.

Cleaning the Mouse
When a mouse gets dirty it behaves erratically. The pointer may not move in one direction or rolling movement may seem very rough. 

Periodic mouse cleaning is easy. Unplug the mouse (shut down your Mac first) and turn it over.  Spin the ball retainer counter clockwise until it loosens. You should now be able to remove the retainer and mouse ball. Looking inside you will notice three rollers. Two detect movement on an X,Y axis the other is just a pressure roller. To clean them you need cotton swabs and alcohol. Moisten the swab with alcohol and rub the rollers until they are clean. You may have to scrub hard to get rid of the ridge of grit that has build up on the rollers.  If the grit is excessively encrusted use the small plastic alignment tool described in the tools section to gently scrape the grit of before finishing with the swab. Reassemble the mouse using the reverse of the disassembly procedure.
To clean the mouse ball rinse it under water. Don't soak it. Then let it air dry. If you wipe it, it will pick up lint.

Mouse Repair

If your cleaning of the mouse does not fix your problems then you may have mouse failure. The failure might be with the mouse or on the logic board
Taking the mouse apart is not difficult. See the section " Mouse disassembly".

Mac Plus Mouse Only
If all items that the pointer touches on the screen are selected follow these steps.

1. If you are able try another mouse with the computer. If the problem persists you most likely have a logic board problem and it will have to be repaired or replaced whichever you decide. Refer to appendix replacing the logic board.

2. If the second mouse works then you have a mouse problem. Most likely the problem is with the mouse switch. Replacing the mouse switch is do-able if you are the least bit handy. See ahead, Mouse Switch Replace.

If the mouse seems to jam to one side or the other or doesn't move at all then the mouse cable is the culprit.

Symptom

Problem

Pointer stuck to right                                  Brown wire is broken
Pointer stuck at top                                    Green wire is broken
Pointer stuck at left                                     Orange wire is broken
Pointer stuck at bottom                              Blue wire is broken
Mouse doesn't work, no pointer              Black and red wires broken

Solution: repair or replace cable See Appendix, Mouse cable repair

ADB Mouse (SE and later)
Many of the same features exist for this mouse. It only has three cables because there is a logic chip in the mouse instead of in the computer like the Plus.  See ahead, Mouse disassembly, Mouse switch replacement, Mouse cable replacement.

Mouse disassembly
Remove the mouse ball by turning the mouse retaining ring on the underside counterclockwise. Next remove the phillips head screw or screws (depending on the model) from the base of the mouse.  Remove the screws. Different mouse models have retaining tabs on the mouse located inside the seam.  Usually they are located near the cord. You will have to press the sides and push away from the screw locations on a Mac Plus mouse. With a little effort the mouse should pull apart.

Mouse switch replacement

Mac Plus (non ADB mouse)
See mouse disassembly above.
You can tell a non ADB Mac mouse because it has an elongated 9 pin connector rather than the round 4 pin (din4) connector.
The mouse switch is of two types. The easiest for you to obtain is one from Radio Shack part number 275-016 or 275-017. The solder tabs will need to be trimmed so they look just like the original. Take extra time to trim the tabs so it will fit just like the original. If you don't your mouse button will not work right.  If there is a switch lever on the switch you will need to remove it. You will also notice that the switch button might be slightly to the side compared to the original. This is okay and it will work right. Solder the switch into place, reassemble the mouse, and keep your fingers crossed that you trimmed the contacts the right height.  You might notice a slightly firmer  feel to the switch. This is normal since your old switch had gotten soft with age and the new switch has a slightly firmer feel than the old originally did.

ADB mouse (Mac SE and later)
The switch of the ADB mouse is specific. Try Radio Shack or you may have to dig deeper. I've included an address for OEM parts in the appendix. The switch is an OEM microswitch, and is an OMRON D2F-D1l83W.  Maybe contact your Apple dealer. They may be willing to sell you one.

Mouse Cable Replacement

Mac Plus
If you have a dead mouse and  determined that the mouse cable is at fault, probably by trying a different mouse and finding that it works. You can repair the mouse cable. Mouse cables usually break within a few inches of the ends. This is because most wire bending occurs at these points.  First try cutting the wire about 2-3 inches from the connector end. Then obtain a new connector (DB-9m) from an electronics supply house) and solder it on. the diagram is shown below.

ADB (SE and beyond)
The same applies as with the Mac Plus mouse except that the connector is different and their are only three wires. Below is the wiring diagram for the DB-4 connector. Also since this type of mouse has a logic chip in the mouse instead of in the computer, the problem could be the electronics in the mouse.

For both types of mice
If you suspect the mouse end of the cable, the break probably occurred within 6-8 inches of the end. This is where most of the bending happens during use. Again try cutting off that much cable and re-soldering it to the mouse.  This is a circuit board soldering job on the ADB type mouse.