Motorola Saber Theory Maintenance 68p81044c05 O Manual

grams in the service manual. When making these volt-
age checks, pay particular attention to any notes that
may accompany the voltage reading of a particular
stage.
Replacing a transistor or module before a thorough
check is made is not recommended. Read the volt-
ages around the suspected stage. If these voltages
are
not
close to those specified, the associated components
should be checked.
A low-impedance meter should not be used for
measurement. If all dc voltages are correct, the signal
should be...

61 of U400.
If there are no indications on either step (a) or (b),
check for the presence of 5Vdc on the common
line of the frequency switch.
(5) Verify with an oscilloscope that the BUSY line (J4,
pin 12) is at a constant 5Vdc level.
NOTE
The BUSY line of U400 reads low only when the
DATA lines (pins 22, 27) are active. This is the case
when the radio is first powered up.
(6) (a) Check the microcomputer data output line
(U400, pins 28, 29) conditions with an oscillo-
scope:
·Condition 1 - With the radio...

NOTE
Both number 1 and number 2 regulators must be
operational for the microcomputer (U400) to func-
tion properly.
(4) Check that the voltage at the collector of number 1
regulator Q1 = 5Vdc. If the voltage is lower than
4.8Vdc or higher than 5.2Vdc, then complete this
step:
(a) Check that the resistance of Q1 collector to
ground = approximately 4k½(negative side of
the probe connected to ground).
(b) Check the bias levels of Q1: emitter = 7.5Vdc;
base = 6.7Vdc. If the levels are wrong, sus-
pect the...

(1) Perform step e (6) before continuing with this pro-
cedure.
(2) Check the output (pin 14) of synthesizer U300:
(a) While keying the radio, measure, with an rf
millivoltmeter, the synthesizer output where it
enters the rf PA (U202, pin 1). A level of 200
to 500mVac should be measured.
1. (Mid-band only). Check L209 for continuity.
2. (VHF only). Check L210 for continuity.
(b) While keying the radio, measure, using a fre-
quency counter with a 50½probe (use the
guide pin of the rf PA module for...

a.(For uhf radios only). The uhf front
end module (U2) and the RX 5Vdc
regulator (U201) will not function if the
FDS module (U203) is not in place.
Turn the radio off, then back on again,
then do the following:
(1) If the FDS module is in place but
there is still no RX 5Vdc at pin 3
of U2, check the voltages on pin 7
(7.4Vdc), pin 8 (0Vdc), and pin 11
(7.5Vdc) of U203 in remote only.
(2) Another indication would be to
key the radio momentarily, then
check RX 5Vdc. If the voltage is
correct, check Q207...

This will affect distortion measurements.
(4) (a) Inject a modulated 1kHz signal (-30dBm) at
capacitor C22. Adjust the radio for rated audio
(3.7Vac) and measure the distortion level.
(b) Check pins 4, 28, and 31 of U102 for 6.5Vac
p-p. At maximum volume, the waveform
should be clipped.
i. Receive Coded Audio 
(SECURENET radios only)
(1) Replace U900 with a SECURENET bypass mod-
ule (NTN4720A). Verify that the radio operates
properly in the clear mode.
(2) (a) Replace U900 with a test module. Ensure...

28
NOTES