TM9-4935-294-15/2
the highest range should be used. If a low range is used
3-16. Rf Head Unit Resistance Chart
in this case, the meter will indicate infinite ohms,
although the actual resistance may be less than a
The operational and troubleshooting t charts trace the
megohm.
fault to the major component or circuit responsible for the
d. In a parallel circuit the total resistance is less
abnormal condition.
To localize the defective
than the smallest resistance in the circuit. This is
component, t unit resistance chart, figure 3-19, and
important to remember when troubleshooting with the aid
observe a through e below.
of the schematic diagrams. When a resistance is
a. When a fault develops in a circuit, its feet will
measured and the value is found to be less than
very often show up as a change in the resistance values.
expected, carefully study the schematic to ascertain that
To assist in localizing such faults the value of each
there are no resistances in parallel with the one that has
resistor is indicated the schematic diagrams, paragraph
been measured. Before replacing a resistor because its
3-14.
resistance measures too low, disconnect one terminal
b. Use a volt-ohmmeter for measuring resistances
from the circuit and measure its resistance again to
in the rf heads. All resistances shown the chart are in
make sure that the low reading was not due to some
ohms, and are measured with the probes connected to
other component of the circuit paralleling the resistor.
the pins of P701 as dicated (1 k ohm - 1, 000 ohms).
e. Before taking readings remove the rf head from
c. When checking circuit continuity, t volt-
the signal source and set FREQUENCY- MC control to
ohmmeter should be set to the lowest resistance range.
the low end of the frequency range.
If a medium or high range used, the meter may indicate
zero ohms, though the resistance may be as high as 5
ohms. When checking high value resistances,
3-76
