September 5, 2008 6881076C25-E
4-42 Troubleshooting Procedures: Power Amplifier Procedures
4.5.1.3.3 Localizing Problems
Failure locations often can be determined by externally measured symptoms. Basic symptoms are
noted below with probable failure locations.
1. Low Power and High Current
- Check for improper load conditions caused by high VSWR external to the radio.
- Check output coax and mini UHF connector.
- Check harmonic filter.
- Check output impedance-matching circuitry from the final device to the harmonic filter.
2. Low Power and Low Current
- If control voltage drive is equal to 8.0 V, then check per the above.
- It control voltage drive is less than 8.0 V, then check the control circuitry.
3. Power Intermittently Low (or Zero) and Current Less than 1 A. When Power Drops
- Check LLA stage.
33 4.0 5.0 0 0.2
TX PA Enable (from U520-25)
34 0 1.3
Control AMP one-shot
35 0 0
Lock (5-V of Synth Out of Lock)
36 0 0.8
Control AMP one-shot
37 10.8 13.6 16.3 10.0 13.0 16.0
A+ (Current Sense +)
38 10.8 13.6 16.3 10.0 13.0 16.0
Current Sense - Voltage Delta 150 mV (30 Watt
only)
39 0 9.2 9.4 9.8
Keyed 9.4-V in
40 1.5 3.0 4.5 1.5 3.0 4.5
Current Limit D-A (max current at 4.5 V)
41 000000
Ground
42 0 2.2 9.6
Control AMP Output (Approx 1/2-V Control)
43 1.3 7.0
Loop Integrator Capacitor
44 2.1 3.2
Control AMP Reference
Q0500E 13.0 13.0
A+ - CR0500 Drop
Q0501C 12.3 12.3
VQ0500E - B/E Drop
Q0501E 0.2 0.2
V pin 23 - B/E Drop
Q0503E 0 1.5
V pin 42 - B/E Drop (TX)
Q0503C 13.6 9.0
Q0504B 13.6 12.9
A+ - B/E Drop (TX)
Table 4-15. Power Control DC Voltage Chart (Continued)
LOCATION
RX MODE TX MODE
COMMENTS
LOW TYP HI LOW TYP HI
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