Test Procedures; Power Output; Tone Deviation; Voice Deviation - GE MASTR II Maintenance Manual

LBI-4896
TEST PROCEDURES
These Test Procedures ar~ designed to assist
you in servicing a transmitter that is operating--
but not properly, Problems encountered could be
low power output, tone and voice deviation, defec-
tive audio sensitivity, and modulator adjust ~on­
trol set too high. Once a defect is pin-pointed,
refer to the ~'Service Check" and the addi tiona!
corrective measures included in the Transmitter
Troubleshooting Procedure. Before starting with
the Transmitter Test Procedures, be sure the
transmitter is tuned and aligned to the proper
operating frequency.
1.
4.
10
CAUTION -------------
Before bench testing the MASTR II Mobile Radio, be sure of the output voltage
characteristics of your bench power supply.
To protect the transmitter power output transistors from possible instant des-
truction, the following input voltages must not be exceeded:
Transmitter unkeyed: 20 Volts
Transmitter keyed (50 ohm resistive load): 18 Volts
Transmitter keyed (no load or non-resistive load): 15.5 Volts
These voltages are specified at the normal vehicle battery terminals of the
radio and take the voltage drop of standard cables into account. The voltage
limit shown for a non-optimum load is for "worst case" conditions. For antenna
mismatches likely to be encountered in practice, the actual limit will approach
the 18 Volt figure.
Routine transmitter tests should be performed at EIA Standard Test Voltages
(13.6 VDC for loads of 6 to 16 amperes; 13.4 VDC for loads of 16 to 36 amperes).
Input voltages must not exceed the limits shown, even for transient peaks of
short duration.
Many commonly used bench power supplies cannot meet these requirements for load
regulation and transient voltage suppression. Bench supplies which employ
"brute force" regulation and filtering (such as Lapp Model 73) may be usable
when operated in parallel with a 12-Volt automotive storage battery.
Wattmete r similar to: 2.
Bird # 43
Jones # 711N
Deviation Meter (with a
.75 kHz scale) similar to:
Measurements # 720
TEST EQUIPMENT REQUIRED
for test hookup as shown:
VTVM similar to:
Triplett # 850
Heath # IM-21
3. · Audio Generator similar to:
GE Model 4EX6Al0
5. Multimeter similar to:
GE TEST SET MODEL 4EX3All,
MODEL 4EX8Kl2 or
20,000 ohms-per-Volt voltmeter
POWER MEASUREMENT
TEST PROCEDURE
1. Connect transmitter output from the antenna jack to the wattmeter through a 50-ohm coaxial cable. Make sure
the wattmeter is terminated into a 50-ohm load.
2. Key the transmitter and check the wattmeter for the desired power output.
SERVICE CHECK
Check the setting of the Power Adjust Control (R216).
Refer to the QUICK CHECKS on the Transmitter Troubleshooting Procedure.
VOICE DEVIATION .. SYMMETRY AND AUDIO SENSITIVITY
TEST PROCEDURE
1. Connect the test equipment to the transmitter as shown.
2. In radios with Channel Guard, set Channel Guard Mod Adjust Rl28 for zero tone deviation.
3. Set the Audio generator output to 1.0 VOLTS RMS and frequency to 1 kHz.
4. Key the transmitter and adjust Deviation Meter to carrier frequency.
5. Deviation reading should be ±4.5 kHz in radios without Channel Guard, and ±3.75 kHz in radios with
Channel Guard.
6. If necessary, adjust MOD ADJUST control Rl27 for the proper deviation on plus
( + )
or minus (-)
deviation, whichever is greater.
NOTES:--- MASTR II transmitters are adjusted for
4.5
kHz deviation at the fa ctor y.
The factory adjustment will prevent the transmi t ter from devi at ing more
than 5.0 kHz under the worst conditions of f r equency, voltage and
temperature.
7. If the deviation reading plus ( + ) or minus (-) di f fers by more than 0.5 kHz, recheck Steps l and 2
as shown in the Transmitter Alig nment Chart.
8. Check Audio Sensitivity by reducing generator output until deviation f al ls to 3.0 kHz for radi os
without Channel Guard, or 2.25 kHz for radios with Channel Guard. Voltage should be LESS than 12 0
millivolts. If not, refer to the Transmitter Troubleshooting Procedure.
AC VTVM
BLACK~
PLUG
~
••
.
...
.
...
AUDIO
LO
TO J11
AUDIO OSCILLATOR
AUDIO HI TO J10
4EX6A10
CHANNEL
MOD ADJUST GUARD MOD
R127 ADJUST R128
ANTENNA
DEVIATION METER
RED SYSTEM
PLUG
TONE DEVIATION WITH CHANNEL GUARD
TEST PROCEDURE
1. Set up the Deviation M eter and monitor the output of the transmitter.
2. Remove the 1000 Hz sig nal from the audio gen e rator.
GE TEST SET 4EX3A 11
POWER ADJUST
CONTROL R216
3. Key the transmitter and check for 0.75 kHz deviation. If the reading is l 0w or high,
adjust Channel Guard MOD ADJUST Rl28 for a reading of 0.75 kHz.
NOTES:
1. On units supplied with Channel Guard, the Phase M odulator Tunj.ng should be adjusted
carefully to insure proper performance. ( Refer to Steps 1 a nd 2 in the Transmitter
Alignment Chart).
2. The Tone Deviation Test Procedures should be repe ated every time t h e Tone Frequency
is c hanged .