R.1.4.1
Minus 15 Volt Power Source
IC U14 provides the negative power supply voltage that is needed
by the various op amps. See sheet 2.
R.2
Maintenance
R.2.1
Adjustments
There are two adjustments on the Switch Board/Meter Panel:
Forward Power Calibrate control A31R14, and Reflected Power
Calibrate control A31R13. These adjustments are made at the
factory by measuring transmitter power output in a calorimetric
dummy load. These calibration adjustments should not be
changed unless some means of accurately measuring transmitter
output power is available. Refer to the Tuning/Frequency Change
Procedure for information on calibrating the reflected power
meter.
R.3
Troubleshooting
R.3.1
Symptom: Incorrect Meter Indications
R.3.1.1
Possible Causes:
a. Metered Parameter (Voltage, Current, or Power) Has
Changed. If possible, check the parameter with another
meter which is known to be accurate. Most parameters can
be checked on other circuit boards in the non-interlocked
compartment. The paragraphs on “Principles of Opera-
tion” above include circuit boards on which various meter-
ing circuits are located.
b. Metering Circuit Fault. Again, refer to the paragraphs on
“Principles of Operation”, above, for location of metering
circuits. Possible faults include:
1.
Operational Amplifier (IC) failure (for PA SUPPLY
VDC, DET NULL, RELATIVE RF DRIVE, REFLD
PWR, and FWD PWR indications). Operational ampli-
fier failure could cause either no indication or a full
scale indication. Voltage followers used as buffer-driv-
ers should have a gain of 1, that is, input and output
voltage should be the same. b. Multiplier resistor
changed value. Most multiplier resistors can be checked
in-circuit, if the multimeter is switched to some other
position to eliminate parallel resistance paths.
2. Faulty Meter Movement. Occasionally, meter move-
ments can change calibration. One way to check a meter
movement is to put the meter in series with a low-cur-
rent source and a microammeter of known accuracy.
Multimeter M1 and power meter M3 have 640 ohm, 100
microampere movements. Supply current meter M2 has
a 10 ohm, 5 milliampere movement.
Prior to starting a troubleshooting procedure check all switches,
power cord connections, connecting cables, and power fuses.
R-2
888-2297-002
Rev. R: 11-11-96
WARNING: Disconnect primary power prior to servicing.
