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Apple Mouse Button Switch Replacement

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Macintosh M0100 mouse parts (Macintosh Repair and Upgrade Secrets Fig 12-1)
Inside the M0100 with the top cover off. The mouse switch sits at the cord end of the circuit board, under the button. Larry Pina, Macintosh Repair & Upgrade Secrets, Figure 12-1.

The Apple Mouse (M0100), used with the Macintosh 128K, Macintosh 512K, Macintosh 512Ke and Macintosh Plus, has a single-pole double-throw microswitch under its button. Dust and hard use make these switches intermittent, and some break outright; clicking then becomes erratic or stops.[1] Cleaning cannot mend worn contacts or broken plastic; the cure is a new switch.[2]

Apple kept the M0100 model number through several internal designs: boards by Alps (one cover screw) and by Mitsumi (two screws), and an earlier "Made in U.S.A." Apple board with two screws.[3] Pina's steps below are written for the one-screw mouse.[4]

Symptoms

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Macintosh M0100 mouse micro switch location (The Dead Mac Scrolls p. 84)
The micro switch under the mouse button. Larry Pina, The Dead Mac Scrolls, p. 84.
  • Clicking is erratic, or does nothing.[1]
  • Everything the pointer touches is selected even with the button up, and other mice work on the same computer: the micro switch in the mouse.[5]
  • The same symptom where this mouse works on other Macs and other mice fail the same way on this Macintosh Plus is a logic board fault: the RC filter (Apple part 115-0002) at A11.[6]
  • Lost pointer movement and button together, coming and going as the cord is flexed, is a cable fault; see Apple Mouse Cable Repair.[7]

See also Macintosh Plus Troubleshooting and Macintosh 128K/512K Troubleshooting.

Safety

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Switch the computer off before unplugging the mouse. Pina notes that the 128K to Plus seem to tolerate live disconnection but the Macintosh SE and II generally do not.[8]

Tools and parts

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  • No. 1 Phillips screwdriver; soldering iron and desoldering tool; analogue meter on R×1K or a digital meter on kΩ.[4][2]
Mouse switch replacement data (Pina, Table 12-1)[2]
Make Part no. Rating, 125 V AC Force Type
Omron SS-01-FD 0.1 A 1.8 oz SPDT, PC mount: M0100
Omron SS-01-FT 0.1 A 1.8 oz SPDT, solder tab: Lisa A9M0050
Radio Shack 275-016 5.0 A 5.3 oz SPDT, solder tab, general purpose
Radio Shack 275-017 5.0 A 5.3 oz SPDT, solder tab, general purpose

Electrically any of these will do. A solder-tab switch must have its lever removed and its tabs trimmed to fit the M0100 board, and the general-purpose types need a firmer press.[2]

Procedure

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Opening the mouse

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Macintosh M0100 mouse retaining ring (Macintosh Repair and Upgrade Secrets Fig 12-2)
The retaining ring. Turn it anticlockwise until the marker points to O. Pina, Figure 12-2.
  1. Shut down, switch off and unplug the computer, then disconnect the mouse cord. Work on a soft towel.[4]
  2. Turn the mouse upside down. The case is marked L (locked) and O (open) beside the retaining ring. Grip the mouse in both hands, press down on the ring with your thumbs and turn it anticlockwise until its marker points to O.[4]
  3. Turn the mouse right side up; the ring and the ball drop into your hand.[4]
Macintosh M0100 mouse underside, two-screw version (Marcin Wichary)
A "Made in U.S.A." M0100 with two screws beside the cord. Pina's one-screw mouse has its screw at the far end. Photo: Marcin Wichary, CC BY 2.0.
  1. Loosen the cover screw with a No. 1 Phillips screwdriver. On the one-screw mouse it is at the end away from the cord; two-screw versions have both screws beside the cord. Turn the mouse over and shake the screws out; if they do not fall out, loosen them further.[4][3]
  2. Release the hidden locking tabs. On the 128K to Plus mouse there are two, beside the cord, and the cover takes a firm push towards the cord to free them; once free, the cover rotates towards the cord.[4]
  3. Lift off the top cover. Take out the button spring, unhook the strain relief from the top cover, and put the spring, the button and the cover aside together. The spring is about 5/8 in long and 1/16 in across; Pina keeps it inside the top cover so that it does not get lost.[4]
  4. Remove the circuit board screw, the smaller of the two screws, so that the board can come out for soldering. On the M0100 the switch is part of the board assembly.[4]

Testing the switch

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  1. Set an analogue meter to R×1K and zero it, or set a digital meter to kΩ.[2]
  2. Clip the probes to the two switch tabs that are wired; ignore the unconnected one. The switch is normally open, so the meter should read infinity or over-range.[2]
  3. Press the switch: the reading must drop to zero at once.[2]
  4. Release it very slowly. A good switch breaks cleanly back to infinity however slowly it is released. A worn one passes through a grey area, typically 500 to 5,000 Ω, which the Mac reads as the button being up while the user is still holding it down.[2]

Fitting the new switch

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Macintosh mouse replacement switches (Macintosh Repair and Upgrade Secrets Fig 12-5)
The original PC-mount switch, a general-purpose solder-tab switch, and the same switch with its lever removed and tabs trimmed. Pina, Figure 12-5.
  1. Desolder and remove the old switch.[2]
  2. If you are using a general-purpose solder-tab switch, remove its lever by squeezing the hinge, then trim and file the tabs to exactly the width and height of the original. Tabs that are too wide damage the board traces when pushed through; tabs that are too tall mount the switch high, and the button is then held down permanently after reassembly.[2]
  3. Fit and solder the new switch. A trimmed general-purpose switch sits slightly off centre; Pina says it works the same.[2]
  4. While the mouse is open, Pina recommends cleaning the capstans and pinch roller (the grey stripes on them are ball build-up) with swabs and head cleaner or a 50/50 mix of isopropyl alcohol and water.[9]

Reassembly

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  1. Refit the circuit board screw.[4]
  2. Put the strain relief back into or onto the bottom cover, and the button spring back into its well.[10]
  3. Lay the button over the switch and spring. The Macintosh Plus button has two protrusions: the star tip goes over the switch and the point goes over the spring.[10]
  4. Set the button position, then angle the top cover over the strain relief so that its tabs line up with the slots. When the tabs interlock the cover snaps into place.[10]
  5. Tighten the cover screw or screws with the No. 1 Phillips screwdriver, holding it between thumb and forefinger and stopping as soon as the screws are snug: the covers are breakable plastic.[10]
  6. Refit the ball and the retaining ring, and turn the ring until its marker points to L.[4]

Testing

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  • With the mouse unplugged, measure between pin 7 (the switch line, yellow wire) and pin 1 (ground, black) of the DB-9 plug. The button grounds pin 7 when pressed, so the meter reads zero with the button down and open with it up.[11][7]
  • Plug the mouse in before switching the computer on, and check that single clicks, double clicks and dragging work and that nothing is selected with the button up.[8][5]
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References

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  1. ↑ 1.0 1.1 Larry Pina, Macintosh Repair & Upgrade Secrets (Hayden Books, 1990), ISBN 0-672-48452-8, chapter 12 "Mouse Repairs", p. 223 (PDF p. 237): the M0100 is the stock 128K, 512K, 512Ke and Macintosh Plus mouse (also Lisa 2/10 and Mac XL); an SPDT microswitch under the button develops intermittents from dust and hard use and sometimes breaks. Hosted as File:Macintosh Repair & Upgrade Secrets.pdf; see Macintosh Repair & Upgrade Secrets.
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 Pina, Macintosh Repair & Upgrade Secrets, pp. 229-231 (PDF pp. 243-245): Table 12-1, switch types, Figure 12-5, testing the mouse switch.
  3. ↑ 3.0 3.1 Glenn Anderson, "Apple IIc mouse compatibility: some details, schematics, and a chip swap to fix compatibility", TinkerDifferent, 2024-2025, accessed 2026-10-25: the Mitsumi mice have two screws and the Alps one; an older Apple-marked "Made in U.S.A." M0100 has two screws and an older style plug; the cords and board connectors differ between makers.
  4. ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 Pina, Macintosh Repair & Upgrade Secrets, pp. 225-227 (PDF pp. 239-241): disassembly.
  5. ↑ 5.0 5.1 Larry Pina, The Dead Mac Scrolls (Peachpit Press, 1992), "Early Macs", p. 84. Hosted as File:The Dead Mac Scrolls 1992.pdf; see The Dead Mac Scrolls.
  6. ↑ Pina, The Dead Mac Scrolls, p. 83.
  7. ↑ 7.0 7.1 Pina, Macintosh Repair & Upgrade Secrets, pp. 231-233 (PDF pp. 245-247).
  8. ↑ 8.0 8.1 Pina, Macintosh Repair & Upgrade Secrets, p. 224 (PDF p. 238).
  9. ↑ Pina, Macintosh Repair & Upgrade Secrets, pp. 227-228 (PDF pp. 241-242): cleaning the capstans, pinch roller and ball.
  10. ↑ 10.0 10.1 10.2 10.3 Pina, Macintosh Repair & Upgrade Secrets, pp. 228-229 (PDF pp. 242-243): reassembly.
  11. ↑ Apple Computer, Guide to the Macintosh Family Hardware, 2nd edition, Addison-Wesley, 1990, chapter 7, p. 278: "The switch on the mouse is a push button that grounds pin 7 on the mouse connector when pressed." Hosted as File:Apple Guide to the Macintosh Family Hardware 2nd Edition 1990.pdf.


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