Service manual

2000 SERIES RECEIVER DECODER MODULE (RDM)
3-20
March 2000
Part No. 001-3139-502
3.12.7 AUDIO DISTORTION
1. Plug a 16 ohm resistive load at J204 on the RFIB
and connect a distortion analyzer to the load.
2. Measure the distortion of the receive audio at J204
on the MAC with the local volume control set to
2.8V RMS.
3. The reading should be less than 3%
(typically < 1%).
4. Measure receive sensitivity at J204 on the Interface
Board.
5. The reading should be < 0.35 µV
(typically < 0.25 µV).
6. The Synthesizer is programmed for 199 channels
above the Receive Channel.
7. The receive sensitivity should be < 0.35 µV
(typically < 0.3 µV).
8. The Synthesizer is programmed for 199 channels
below the Receive Channel.
9. The receive sensitivity should be < 0.35 µV
(typically < 0.3 µV).
3.13 FULL RDM - ALL TEST
1. Select the TEST - FULL RDM - ALL TEST and
press Enter.
NOTE: All audio generators and audio voltmeters are
unbalanced unless specifically stated otherwise.
3.13.1 VOLTAGE MEASUREMENTS
Disconnect the receiver-to-interface cable (20-
pin) from J201 of the interface board.
Measure the voltages at the following pins.
U221, pin 1 +12V DC ±0.4V
U223, pin 2 +9V DC ±0.4V
U224, pin 2 +5V DC ±0.2V
U204, pin 7 +1.25V DC ±0.06V
Junction of L202/C279 -0.5V DC ±0.4V
Apply power to the Receiver by plugging the 20-
pin cable from the Interface Board into J201 (see
Figure 3-32
).
3.13.2 RECEIVER FREQUENCY CHECK
1. Check the receiver injection frequency with a
"sniffer" pickup loop, or RF probe and a suitable fre-
quency counter placed near L210.
2. TCXO Adjustment
Standard 800 MHz: Adjust Y201 for the Injection
frequency (chnl freq-52.95 MHz) ±50 Hz.
900 MHz and High Stability 800 MHz: Adjust Y201
for 3.5V DC (±0.05V) at TP1 (response time is very
slow).
Receiver Audio Distortion Measurement
1. Adjust the RF generator for 100 µV into the receiver
with a 1 kHz tone at ±3 kHz dev (±1.5 kHz for 900
MHz).
2. Adjust R207 for 0 dBm (775 mV RMS) at J210.
3. Connect a 16 ohm load and distortion analyzer to
J204 of the Interface Board.
4. Adjust R262 for 2.8V RMS and measure the distor-
tion. Distortion should be < 3%.
Receiver Hum and Noise Measurement
1. Adjust the RF generator for 100 µV into the receiver
with a 1 kHz tone at ±3 kHz (1.5 kHz at 900 MHz).
2. Connect a 16 ohm load and distortion analyzer to
J204 of the Interface Board.
3. Adjust R262 for 2.8V RMS.
4. Remove modulation from the RF generator. The
measured level must be ≤ -45 dB.