Service manual

2000 SERIES RECEIVER DECODER MODULE (RDM)
3-19
March 2000
Part No. 001-3139-502
3.12.2 VOLTAGE MEASUREMENTS
Apply power to the Receiver by plugging the 20-
pin cable from the RF Interface Board into J201 (see
Figure 3-32
).
Measure the voltages at the following pins.
U206, pin 1 +12V DC
±0.4V
U207, pin 1 +12V DC ±0.4V
U208, pin 1 +6V DC ±0.2V
U210, pin 1 +12V DC ±0.4V
3.12.3 PROGRAM TUNE-UP CHANNEL
1. Using the PC and software, program the Synthesizer
for the Receive channel number.
2. Tune the VCO helical L220 for +4.5V DC ±0.05V
on U209, pin 6 or TP2.
3. Alternately tune L223 and L224 in 1/2-turn to 1-turn
increments until a voltage is measured on J201, pin
13 or TP5. At that time, tune L223 for a peak, then
L224 for a peak.
4. Retune L223 and L224 for a peak at J201,
pin 13.
NOTE: The Channel Number, Channel Frequency and
Synthesizer Frequency appear at the bottom of the
screen.
3.12.4 TCXO FREQUENCY ADJUST
1. Tune Y201 (TCXO) for 3.5V DC ±0.05V at TP1
(response time is very slow).
2. Place a pick-up loop (sniffer) or RF probe connected
to a frequency counter near L210.
3. Verify the Injection Frequency ±90 Hz
(Inj Freq = chnl freq - 52.95 MHz).
3.12.5 VCO TEST
1. The Synthesizer is programmed for 199 channels
above the Receive Channel.
2. The voltage on U209, pin 6 (TP2) should be
< 7.5V DC.
3. Record the voltage on J201, pin 13 (TP5) ____.
4. The Synthesizer is programmed for 199 channels
below the Receive Channel.
5. The voltage on U209, pin 6 (TP2) should be
> 2V DC.
6. Record the voltage on J201, pin 13 (TP5) ____.
7. If the voltages recorded in Steps 3 and 6 are not
within ±0.2V, tune L224 as required to balance the
voltage readings.
8. The Synthesizer is reprogrammed for the Receive
Channel.
3.12.6 FRONT-END ADJUSTMENTS
1. Set the signal generator to the Receive Channel at a
level sufficient to produce an output voltage on
J201, pin 7 (TP3) (RSSI Output).
2. Tune L204, L205, L206, L201, L202, L203 and
L204 for a peak voltage on J201, pin 7 (TP3).
Decrease the generator output level to maintain a 2-
3V reading at J201, pin 7.
3. Set the generator to 1000 µV with a 1 kHz tone at
±1.5 kHz deviation (100 µV at the Rx antenna with
20 dB pad on the generator).
4. Adjust the Quadrature detector coil (Z213) for 2V
DC on U202, pin 9.
5. Adjust R264 for 387 mV RMS, ±5 mV RMS, on
J201, pin 9.
6. Adjust R284 for 2V DC ±0.05V DC on J201, pin 9
(TP4).
7. Set generator to the channel frequency
(±1.5 kHz deviation at 1 kHz tone) at a level that
produces 2V DC on J201, pin 7 (TP3 RSSI).
8. Tune L207, L209, L211 and L225 (and C373/C375
if installed) for peak voltage on J201, pin 7 (TP3).
Decrease the generator output level to maintain 2-
3V DC. Distortion should be <5% (typically < 3%).
9. Repeat Steps 4, 5 and 6.