Voltage Measurement And Signal Tracing - Motorola ASTRO Digital Saber Service Manual

Voltage
Measurement and
Signal Tracing
9 2
-
Equipment for Servicing ESD Sensitive Products," available from
Literature Distribution.
Motorola
Literature Distribution
2290 Hammond Drive
Schaumburg, IL 60173
(708) 576-2826
6. Always wear a conductive wrist strap when servicing this
equipment. The Motorola part number for a replacement wrist
strap that connects to the table mat is 42-80385A59.
It is always a good idea to check the battery voltage under load. This
can be done by measuring the OPT_B+ pin at the universal connector
on the back of the radio, with the radio keyed. The battery voltage
should remain at or above 7.0Vdc. The battery should be recharged or
replaced as necessary prior to analyzing the radio.
In most situations, the problem circuit may be identified using a dc
voltmeter, RF millivoltmeter, and oscilloscope (preferably with
100MHz bandwidth or more). The "Recommended Test Equipment,
Service Aids, and Tools" section in the ASTRO Digital SABER Portable
Radios Basic Service Manual outlines the recommended tools and
service aids which would be useful. Of special note is the REX-4200A
Housing Eliminator, which allows the technician to open the radio to
probe points while in operation.
In some cases dc voltages at probe points are shown in red on the
schematics. In other areas diagrams are included to show time varying
signals which should be present under the indicated circumstances. It
is recommended that a thorough check be made prior to replacement
of any IC or part. If the probe point does not have a signal reasonably
close to the indicated one, a check of the surrounding components
should be made prior to replacing any parts.
!
C a u t i o n
When checking a transistor or module,
either in or out of circuit, do not use an
ohmmeter having more than 1.5 volts
dc appearing across test leads or use an
ohms scale of less than x100.