Chapter 7: Mice

Clean mice as all other plastic computer equipment, do not bend LEDs and photodetectors inside if you don't know what do you want to tune. If you don't remember ball-based mice, you should know that these shafts which are rotated with ball should not be covered with dirt.  In some mice it may be needed to replace microswitches (especially Amiga mice or late-90s PC mice made by Genius).

Mouse works by translating moves to electric signals. Ball rolls and actuates horizontal and vertical shafts. These shafts rotate discs with holes. The se discs pass and interrupt lighs from infrared LEDs to phototransistors so the speed can be figured out from the signal.
The direction of move is detected by using two detectors in some distance. When the change (light interrupt) is detected on one detector first, the directioin is forward, if the second goes first - backward. Sometimes two detectors are combined in one casing, in other cases it is made using two LED-phototransistor parts on both sides of the disc.
Alternating waves can be converted to digital form and passed to computer or converter to data packets by mouse electronics and sent to PC by some serial connection.

So if your mouse works perfectly when opened, but closed casing makes it not work it means that light doesn't pass to detector. You can tune it moving one of problematic LEDs/detectors a bit.
Before, check do the LEDs work. They emit infrared, so it won't be possible to see their emission, but some cheap CMOS cameras can convert it to visible traces on a photo - just see these LEDs in a dark room using a cell-phone camera.

Principle of operation of a typical computer mouse

There are many kinds of computer mice interfaces. Examples are:

1. Serial port - the most common in old PCs, before PS/2 port era, mouse with female DB9 connector. These mice will work usually only with PCs, in DOS they need a driver. Serial port is a connection which is used to get information to computer, but information may be packed in different "languages". There are two of serial mouse standards: "Microsoft" one (or "Logitech", "Dexxa", etc.) being a de-facto standard, or older "Mouse Systems PC Mouse" standard which is different and requires another driver. If you plan to run certain old software (such as VisiCorp Visi-On) on your PC you may need the mouse with PC Mouse standard. Some mice have a switch allowing to switch between "Microsoft" (2-button) and "PC Mouse" (3-button) modes. Sometimes this switching can be done by holding the left mouse button at the power-up of the system.

2. Phase detection - this mouse sends four square waves, a pair for each direction. The shift between these waves is interpreted as cursor moves. These mice are not common in PCs (probably only early Microsoft Bus Mouse is such animal, and it requires a special ISA expansion card), but they are standard in early Macintosh (before ADB), Amiga or Atari ST, maybe early Siemens PCs. My universal mouse is such mouse which can be made of any old computer mouse.

3. Key pressing - These are rare and specific for a computer model. Moving in specific direction gives pulses on specific data lines or toggling specific keyboard scan codes. They were used only in some rare PC clones and early Amstrad PCs.

4. Analog - Mouse emulates a paddles with analog knobs. The only usage of this method I know is some strange Commodore 64 mouse.

5. ADB - Special interface designed for keyboard and mice in early (pre-USB) Apple Macintosh computers.

6. PS/2 - mouse and keyboard interface for IBM PS/2 and PS/1 computers, later spread to all PCs instead of serial port. Some PS/2 mice may work as a serial mice with a converter, but not all.

7. Other proprietary connections - e.g. Sun's mice connected to keyboard - they are usually some serial connections, but require the proper hardware.
These interfaces are not interchangeable without active (usually microprocessor-based) converters. Phase detection mice can be usually connected to another machine but only when special pinout converter is made.

MOUSE Diagnostic checklist:
0. Clean it. Especially rollers and shafts. Works better?
1. Check cable with ohmmeter. If doesn't work, in 90% cases it needs to be cut and re-soldered, and the break is near mouse. I usually cut it leaving 6-10cm in mouse, then re-solder it to mouse's internal connector's plug. having a few cm of wires left from it.
2. If it still doesn't work, try touching chip on PCB.Maybe a broken solder?
3. If it's still not detected, suspect other broken solders or electronics. IF it is detected, but cursor is not moving...
4. Rotate the X/Y wheels by hand - test axes. Try to slightly (!) move receiver (receiver is not transparent) spinning the wheel in a good lit environment - does it move cursor? If it looks like it works, try to calibrate it by moving the receiver.
5. If it works in light, but doesn't when mouse is closed, the culprit is transmitter's position. Usually too close to wheel.
6. Check button contacts, do they require resoldering or replacing?
7. Bad solders on transmitters/receivers?
8. Now you can suspect electronics.

Chapter 6: Keyboards
Table of contents

Chapter 8: Joysticks

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