Test Procedures; Power Output; Tone Deviation; Voice Deviation .. Symmetry And Audio Sensitivity - GE MASTR II Maintenance Manual

LBI-4898
TEST PROCEDURES
These Test Procedures arB 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 con-
trol set too high. Once a defect is pin-pointed,
refer to the "Service Check" and the additional
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 volta ge
characteristics of your bench power supply.
To protect the transmitter power output transistors from possible instant des-
truction, the f ollowing input voltages must not be exc eede d:
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 ~ccount. 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 test s should be performed at EIA Standard Test Voltages
(13.6 VDC for loads of 6 to 16 amperes; l3 o4 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 filt er ing (such as Lapp Model 73) may be usable
when operated in para llel with a 12-Volt automotive storage batterya
Wattmeter similar to :
2.
Bird # 43
Jones # 711N
Deviation M e ter (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 M ODEL 4EX3All,
MODEL 4EX8Kl2 or
20,000 ohms ~per - Volt voltmeter
POWER MEASUREMENT
TEST PROCEDURE
1. Connect transmitter output f rom t he antenna jack t o the wat tme ter through a 50- ohm coaxial cable . M ake s u r e
the wattmeter is terminated into a 50- ohm load.
2. Key the transmitter and check the wat tmete r for t he desired power output .
SERVICE CHECK
Check the setting of the Power Adjust Control ( R26l ) .
Refer to the QUICK CHECKS on t he Transmitte r Troubleshoot i ng Pr ocedur e .
VOICE DEVIATION .. SYMMETRY AND AUDIO SENSITIVITY
TEST PROCEDURE
l. Connect the tes t equipment to the transmitter as shown.
2. In radios with Channel Guard, set Chan nel Guard Mod Adjust Rl28 f o r zero tone deviation.
3. Set the Audio generator output to 1.0 VOLTS RMS and frequency t o 1 kHz.
4. Key the transmitter and adjust Deviation Me ter 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. I f necessary , adjust MOD ADJUST control Rl27 for the proper deviation on plus (+) or mi nus (- )
deviation, whichever is greater.
NOTES:-- MASTR II tra n smit te rs are adjusted for 4.5 kHz deviati on at the fac tor y .
The fa ctory adjustment wi l l prevent the transmitte r from devia ting more
than 5.0 k Hz under th e worst c onditions of f requency, v oltage and
temperature.
7. If t he deviat ion rea d ing plus
(+)
o r minus ( - ) di ffers by more t ha n 0.5 kHz, recheck Steps l and 2
as shown in the Transmitter Alignment Chart .
8 . Check Audio Sensitivit y by r e ducing generato r output unt i l devi a t ion fal l s to 3 .0 kHz for radios
without Channel Guard, o r 2.25 kHz for radios wi th Channe l Guard . Vo ltage should be LESS than 120
mi l livolts. I f no t, refer to t he Transmit t er Troub leshoot i ng Pr ocedu re.
ACVTVM
BLACK~
PLUG
Y'
ANTENNA
DEVIATION METER
AUDIO OSCILLATOR
4EX6A10
AUD IO
LO
TO J1 1
AUD IO HI TO J1 0
CHANNE L
MOD ADJUST GUARD MOD
R127 ADJUST R128
RED SYSTEM
PLUG
TONE DEViATION WITH CHANNEL GUARD
TEST PROCEDURE
l. Set up the Deviation Mete r and mon i tor t he ou tpu t of t h e transmi tt er.
2 . Remove the 1000 Hz si g nal from t he audi o gene r a tor .
GE TEST SET 4EX3A 11
POWER ADJUST
CONTROL R261
3. Key the transmi tter and check fo r 0.75 kHz d evi a tion . I f t he readin g is l ~w or h i gh,
adjust Channel Guard MOD ADJUST Rl28 for a read i ng of 0 . 75 kHz .
NOTES:
1. On un its supplie d with Channel Guard, t h e Phase M odulator Tunin g shou l d be adjusted
carefu ll y to i nsure proper performance . (Refer to S t eps l an d 2 in the Transmi t t er
Al ignme nt Cha rt ) .
2. The Tone Deviation Tes t Procedures s hou l d be repeated ever y t ime the Tone Freq uency
is chang e d .