8525B/8528 Technical Service Manual 6-1
Publication No: 15-02036 Issue 6
6 Maintenance
6.1 General
6.1.1 CMOS Devices
A number of Complementary Metal Oxide Semiconductor (CMOS) devices
are used in the transceiver. Although protection is built into most of these,
their extremely high open-circuit impedance makes them susceptible to
damage from static charges. Care must therefore be used when shipping and
handling the devices and in servicing equipment in which they are installed.
The following precautions should be observed:
• Packaging—Replacement CMOS devices are supplied in special
conductive packaging. They should be left in this packaging until
required for use.
• Switch off—Ensure that supplies are switched off before disconnecting
or reconnecting any connections between circuit boards and the
remainder of the transceiver.
• Handling—Handling of circuit boards and particularly touching any
conductive parts should be kept to a minimum.
• Grounding—Anything connected to or touching the circuit board tracks
should be grounded. Observe the following:
- Test equipment connected to a board should be grounded via its
mains lead.
- Static charges which may build up on the person can be discharged
by touching a grounded metal surface with both hands. This should
be done before, and at frequent intervals while, working on circuit
boards.
- Wearing a suitably grounded conductive wrist strap will minimise
the static build up on the person.
6.1.2 Circuit Boards
When servicing printed circuit boards the following should be observed:
• Excessive heat—Excessive heat may lift the track from circuit boards,
causing serious damage. Avoid the use of high powered soldering irons:
a 60W maximum iron, preferably temperature controlled at
approximately 370°C, is sufficient for most tasks. A slightly higher
temperature (425°C) iron may be required for heavier components such
as PA transistors. Apply the iron only long enough to unsolder an
existing joint or to solder a new one.
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