Safe Handling Of Cmos Devices; Disassembling And Reassembling The Mth500 Unit - Motorola MTH500 Service Manual

Maintenance

Safe Handling of CMOS Devices

Disassembling and Reassembling the MTH500 Unit

5 - 2
Complementary metal-oxide semiconductor (CMOS) devices are used in the radio. While the
attributes of CMOS devices are many, their characteristics make them susceptible to damage
by electrostatic or high voltage charges. Damage can be latent, resulting in failure occurring
weeks or months later. Therefore, special precautions must be taken to prevent device damage
during disassembly, troubleshooting, and repair. The following handling precautions are
mandatory for CMOS circuits, and are especially important in low humidity conditions.
• All CMOS devices must be stored or transported in conductive material so that all ex-
posed leads are shorted together. CMOS devices must not be inserted into conventional
plastic "snow" or plastic trays of the type that are used for storage or transportation of
other semiconductor devices.
• All CMOS devices must be placed on a grounded bench surface and the technician must
also be grounded before handling the devices. This is done most effectively by having
the technician wear a conductive wrist strap in series with a 100kW resistor to ground.
• Do not wear nylon clothing while handling CMOS circuits.
• Do not insert or remove CMOS devices with power applied. Check all power supplies
to be used for testing CMOS devices and be certain there are no voltage transients
present.
• When straightening CMOS device leads, provide ground straps for the apparatus used.
• When soldering, use a grounded soldering iron.
• All power must be turned off in a system before printed circuit boards containing CMOS
devices are inserted, removed, or soldered.
Mechanical checks and self tests should be performed on the unit at the basic level of service.
To perform testing at the field level, it is sometimes necessary to remove the antenna and the
housing from the unit. Procedures for disassembling and reassembling the unit are described
in the sections that follow.
NOTE: Read each procedure thoroughly before performing the actual task.
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