39
Symptom Possible Cause Correction or Test (Measurements Taken at Room Temperature)
RF sensitivity poor 1. Synthesizer not on Check synthesizer frequency; if off by more than 250Hz, go to synthesizer
frequency/working troubleshooting chart.
2. Antenna switch Check insertion loss from antenna connector to Rx front end coax from the PA; if loss
(amplifier board) is less than 1.5dB, the problem is in the transceiver housing.
3. Receiver front-end a. Measure the gain of the front-end assembly by injecting a signal at the desired
assembly or VCO board receive frequency and measuring the output level at 109.65 MHz; net conversion gain
should be > 6dB.
b. If conversion gain is < 6dB, check the supply voltage fed into the front end on the
center conductor of the output coax to the RF board; if it is less than 9V, check the
RF board.
c. Check the injection level from the VCO board; if it is less than +2dBm, replace the
VCO board; if injection is OK, replace Rx front-end assembly.
4. RF board Check the sensitivity into the RF board @ 109.65 MHz. If greater than –118.5dBm,
replace the RF board (CAUTION: there is 12.5Vdc on the center conductor of this coax;
a dc blocking capacitor must be used here.)
Radio will not RF board or command board a. With no RF signal applied to the radio, advance squelch control to maximum setting
squelch (15). Is there > 3.0 Vp-p of noise on pin 4 of J500? If not, replace RF board.
b. Is there > 2 Vp-p @ pin 6 of J500? If not, replace RF board.
c. Is there > 2 Vp-p @ pin 5 of J500? If not, replace command board.
d. Is pin 8 of J500 > 2V? If so, replace RF board; if not replace command board.
Radio will not 1. On/off switch Check for SWB+ at pin 31 of J0502 on the command board. If not there, check for SWB+ at
turn off (Control head) pin 4 of P103 on the control head.
2. Command board Does SWB+ on pin 31 of J502 switch on and off as the control head switch is operated?
If so, replace the command board.
Excessive noise in 1. Check programming Make sure HearClear is enabled.
fading conditions
2. RF board a. Is there > 3 Vp-p of noise on pin 4 of J500 with no signal applied? If not, replace
RF board.
b. Apply a –100dBm signal to the antenna connector at the desired frequency; measure
RSSI voltage (pin 9 of J500); increase the RF signal by 10dB; the RSSI voltage
should increase by 180mVdc; if not, replace the RF board.
Table 13. Receiver Troubleshooting Chart
(continued)
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