Troubleshooting 3-21
3.3.4.2.2 Troubleshooting the Driver Amplifier
1. Check for blown fuses F2400, F2100. If any of these fuses is blown, this indicates a
damaged device that has shorted to ground. Inspect for failures downstream. If Q2300
has failed, it cannot be repaired and the kit must be replaced.
2. Apply 28.6 V and 14.2 V main DC supplies. Measure output voltage at pin 2 of U2500
linear regulator; it should be ~28.6 V. Measure drain voltage at final driver stage U2300
pins 13 and 23; they should be ~28.6 V.
3. Enable the PA, and measure output voltage at pin 2 of U2500 linear regulator; it should
be ~25 V, when PA is enabled. Measure drain voltage at final driver stage U2300 pins 13
and 23; they should be ~25 V.
4. Key the PA to rated output power, and measure drain voltage at final driver stage U2300
pins 13 and 23; they should be ~25 V.
5. Measure V_Omni at pin 4 of Q2400; it should equal ~1.5 times V_Control at M2023.
6. Measure pin 3 of predriver stage Q2100 (AH101 device); it should equal a few volts
below V_Omni. If it is notably less than this, the AH101 device is damaged and should
be replaced.
7. Measure pins 10 and 20 of final driver stage U2300; they should equal 2 V to 3 V each.
8. If no issues are found in the steps above, and the 28 V current indicates a final amplifier
related issue, perform troubleshooting steps on the Circulator and Output Board. This
can be additionally verified by sniffing the RF levels at the various stages of the driver to
ensure that the correct diagnosis has been performed.
9. If no issues are found in the steps above, and 28 V current does indicate increased final
amplifier current draw with increased V_Control, perform the final amplifier
troubleshooting steps.
When working on the RF Board, do not use a heat gun or hot
plate. Damage to the circuit board can result.
Do not attempt to replace RF amplifier devices Q2300,
Q4300, Q4400, Q4500, or Q4600 on the RF Board. If any of
these devices fail, the entire RF Board kit must be replaced.
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