Internal Layout; Special Topics; The Touch Screen - Zeiss humphrey HFA II-i series Field Service Manual

General Information
7. Do not rub the inner bowl surface while attempting to clean it; rubbing will cause a
noticeable polished area in the bowl.
8. Do not touch the glass surface of the projection lamp with your bare fingers. Any oil, dirt
or grease on the lamp can shorten its effective life and diminish light output.
9. Do not place items on top of the unit; the internal mechanism of the instrument is very
close beneath the top cover.
10. Ensure that none of the ventilation openings in the instrument are blocked. Excessive
heat buildup within the instrument can cause instrument failures.
11. DO NOT flex the circuit boards. This instrument uses multilayer circuit boards. Multilayer
circuit boards are inherently susceptible to damage by excessive flexing.
12. Proper ElectroStatic Discharge (ESD) precautions must be observed whenever you are
disassembling or handling the instrument's circuitry. Many of the components are
extremely vulnerable to static discharge damage. A Field Service Static Protection Kit is
available for order and must be used for ESD protection during service of this instrument.
Refer to Appendix A for details regarding this kit.
13. An abrupt, harsh noise will ensue if the chinrest comes up against its travel limit during
chinrest movement. Moving the chinrest up against its limits for a few seconds causes no
mechanical harm.
1.6

Internal Layout

The parts drawings in Section 7 of this Field Service Guide illustrate the internal physical
layout of the instrument. Diagrams in Section 6 illustrate the functional layout of the
instrument.
1.7

Special Topics

1.7.1

The Touch Screen

The HFA II - i uses a transparent, analog, resistive-membrane touch screen. It is constructed of
two pieces of thin, highly linear, electrically conductive film (Indium Tin Oxide). The two
pieces of film are separated by a small air gap. The air gap is maintained by small (.001"),
dielectric spacer dots.
Each film sheet has a set of parallel bus bars applied along opposite edges of the film. The two
sheets are oriented so that the bus bars on one sheet are perpendicular to those on the other
sheet. Slight pressure will cause the conductive surfaces to come into contact. The location of
the contact point can be detected by a logic circuit measuring the voltage found at that
particular point.
The analog type of touch screen gives a "voltage divider" analog response that allows
positional determination.
Field Service Guide
Humphrey Field Analyzer II - i
Confidential and Proprietary
1 - 10 52235C1105