3-24 Troubleshooting
3.3.4.2.7 Troubleshooting the Power Control Loop
If the individual pieces of the PA are working properly, the power control loop response should be
verified. For this, the entire loop will be checked to make sure it is working properly.
1. Apply 28.6 V and 14.2 V main DC supplies.
2. Check 3.3 V regulator output U6050 pin 2 to make sure it is ~3.3 V.
3. Check 5 V regulator output U6060 pin 2 to make sure it is ~5 V.
4. Key the PA to rated output power, and measure V_Forward at M8003; it should increase
with output power to several volts at rated Pout. If not, replace Output Board.
5. If using a mule base station/repeater to control the PA, when keyed, pin 16 of U6170
should decrease with increased output power, ranging from ~3.3 V in standby mode and
down to lower voltages for increased output power. Likewise the output on pin 14 of
U6410 should track, as it is a level shifted version of the voltage on pin 16 of U6170.
6. If output power can be manually set using method 2 or 3 of the setup, but cannot be set
using method 1, this would indicate an issue with the SPI circuitry, which could include
the NVM, DAC, or CPLD devices, or with the communication lines for SPI
communication. The ribbon cable to the backplane should be replaced first to determine
if that is the issue.
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