Nautel NX15, Troubleshooting Manual

Page: 59 / 274

NX25/NX15 Troubleshooting Manual Responding to alarms
Issue 5.0 2016-05-06 Page 1-51
Power Amplifier FET replacement
See Figure 1.5 on page 1-52 .
1. Remove five M3 screws that secure the modulator/power amplifier PWB to the chassis.
2. Remove 16 M4 screws (four for each MOSFET) that secure the PWB to the MOSFETs.
3. Swing the PWB away from the chassis and remove two M4 screws that secure the defective
MOSFET to the chassis. If necessary, remove the screw securing the thermistor wire to the
PWB.
4. Discard the defective MOSFET and its associated thermal pad (between MOSFET and
chassis).
5. Ensure the surface of the chassis/heat sink is clean and free of debris.
6. Obtain a replacement MOSFET (Nautel Part # QR) and a new thermal pad (Nautel Part #
HAK55) from the spares kit, if purchased, and install them on the RF power module chassis
using the two M4 screws removed in step 3. Torque hardware to 12 in-lbs (1.3 N-m).
7. Replace any other defective MOSFETs and then re-install the PWB to the chassis by
reversing the instructions in steps 1 through 3. Torque the 16 MOSFET screws (four for
each MOSFET) to a maximum of 10 in-lbs (1.1 N-m).
8. Return the power module to service (see “Installing an RF power module” on page 1-47 ).