User Manual
SERVICING
5-2
June 1997
Part No. 001-3412-002
Control Voltage
Check the DC voltage at TP831 with a channel
near the center of the band. If the VCO is locked on
frequency, this should be a steady DC voltage near
3V. If it is not locked on frequency, it should be near
the lower or upper end of its range (0V or 5.5V).
Output Frequency
Check the VCO frequency at R893. If the VCO
is locked on frequency, it should be stable on the
transmit channel frequency. If the VCO is not locked
on frequency, the VCO control voltage is probably
near 0V or 5.5V.
5.2.4 SYNTHESIZER (U801)
Lock Detector
When the VCO is locked on frequency, the lock
detect output on J201, pin 7 should be high.
5.3 RECEIVER SERVICING
To isolate a receiver problem to a specific sec-
tion, refer to the troubleshooting flowchart in Figure
5-1. Tests referenced in the flowchart are described in
the following information.
NOTE: Supply voltages are provided by the user.
5.3.1 SUPPLY VOLTAGES AND CURRENT
Measure the supply voltages on the following
pins at interface connector J201:
Pin 2 - 13.3V DC nominal
Pin 3 - 0.0V DC while in Receive
Pin 4 - 3-16V DC in Receive Mode
Pin 5 - 3-16V DC
Pin 6 - 2.5V DC ±1%
Place a DC ammeter in the supply line to the
transceiver and the following maximum currents
should be measured:
Pin 4 - 150 µA
5.3.2 MIXER/DETECTOR (U241)
Data Output
Using a .01 µF coupling capacitor, inject a
52.95 MHz, 1 mV signal, modulated with 1 kHz at
± 3 kHz deviation at U241, pin 1. The signal output at
U241, pin 8 should be approximately 150 mV P-P.
NOTE: This signal consists of the 1 kHz modulation
and harmonics of 450 kHz.
RSSI Output
The RSSI output on J201, pin 12 should be
<900 mV DC with no signal applied, and >2.3V DC
with a 1 mV input signal.
Figure 5-1 RECEIVER SERVICING
START
MEASURE CURRENT
OK
?
OK
?
NO
YES
YES
NO
REFER TO SECTION 5.3.2
CHECK FUSES AND
WIRE HARNESS CONNECTIONS
REFER TO SECTION 5.3
AND VOLTAGES
CHECK DATA
OUTPUT
REFER TO SECTION 5.3.2
CHECK
CHECK AUDIO
OK
?
YES
NO
OK
?
YES
NO
CHECK MIXER/
DETECT CIRCUIT
U241
CIRCUIT
REFER TO SECTION 5.3.4
REFER TO SECTION 5.3.3
REPLACE DEFECTIVE
COMPONENT
REFER TO SECTION 5.3.6
CHECK BUFFERS
CRYSTAL FILTERS
REPAIR DEFECTIVE
STAGE
CHECK RF AMP
FIRST MIXER
REFER TO SECTION 5.3.3