Mouse-wheel fix

The mouse wheel on the mouse that came with the Dell 8100 stopped working. Or at least is worked intermittently. If you moved your finger v-e-r-y slowly, you could get scroll to move. But the detent was too stiff for rapid moves. And of course applying more pressure clicked the middle button. I decided that there was slippage and determined to find out why.

Disassembling a mouse is typically one-screw removal. On the Dell mouse, it in the center of the bottom approximately in line with the screw in Figure 1. After removing the screw, separate the shell halves. On this Dell this seemed a bit tricky. There are two tabs on the front of the top shell that insert into pockets in the bottom shell. These pockets can be seen in the nearest part of figure 1. A certain amount of force is require to overcome the springiness and friction. When you separate the top from the bottom, the mouse wheel will probably come loose as it is retained on the top by posts on the top half-shell. It rests in half-journals on the bottom. The skinny end inserts into the detent/switch component on the circuit board. The fat end is over the micro-switch (black component with white bar) which is farther away on the left. The other two micro-switches are for the right and left buttons.
The tire has been rolled off of the hub in Figure 1. What I found was that there was an oily substance between the hub and the tire. I used a piece of tissue, water with a touch of detergent (actually still in the sink from the lunch dishes) to clean the hub and the inside of the tire.

Re-assemble the tire to the hub. Insert the small end of the shaft into the detent/switch as you set the wheel assembly into its bearings. Press the wheel down to verify micro-switch click. Rotate the wheel an verify that the detent works as it turns. Carefully insert the two tabs on the front of the top half-shell into the two pockets that can be seen out-of-focus in Figure 2 beyond the wheel. There is a critical angle and pressure that bends everything just enough. Once the tabs are inserted, lower the top half-shell until it is closed. Re-insert the screw. When re-installing a screw, it is a good idea to rotate in the removal direction (counter-clockwise) until you feel the click of the threads. Then proceed to tighten. This is especially true of self-tapping screws as it is desirable to re-use the original thread, not cut a new one.
Plug the mouse into a computer and test its function.
While I did not disassemble another mouse, a Dynex, I noted that the screw is not visible. If you do not see a screw, probe or remove any label on the bottom to locate a screw. Another possibility is a snap-together arrangement. I suspect the insides will be similar to the pictures of the Dell mouse.