upgrading and repairing PCs technicians ... - 400 Bad Request

220
Chapter 9—Keyboards, Mice, and Input Devices
Table 9.5 Mechanical Keyswitch Types Compared
Keyswitch Type
Pure Rubber-
Feature Mechanical Foam Dome Membrane
Tactile Usually a Minimal Soft No click
feedback click feedback click
Durability High: 20- Variable: High: Rubber Extreme: No moving
and million Contacts dome protects parts, sealed unit
serviceability keystroke can corrode; contacts from for harsh industrial
rating easy to
clean
corrosion environments
The pure mechanical type of keyboard, often using Alps
keyswitches, is second only to the keyboards using capacitive
switches in terms of tactile feedback and durability. Capacitive
keyswitches are rated for up to 25 million keystrokes. Traditionally,
the only vendors of capacitive keyswitch keyboards have been IBM
and the inheritors of its keyboard technology, Lexmark and
Unicomp.
Cleaning a Foam-Element
Keyswitch
Figure 9.1 shows a foam-element keyswitch, often found in keyboards
sold by Compaq and keyboards manufactured by
Keytronics.
Key top
Return
spring
Flexible
foam
Foil layer on
bottom of foam
Contacts on
circuit board
Figure 9.1 A typical foam-element mechanical keyswitch.
The foil contacts at the bottom of the key and the contacts on the
circuit board often become dirty or corroded, causing erratic key
operation. Disassemble the keyboard to gain access to the foil pads,
clean them, and treat them with Stabilant 22a from DW
Electrochemicals to improve the switch-contact quality.