Nautel NV3.5, Troubleshooting Manual

Page: 43 / 228

NV5/NV3.5 Troubleshooting Manual Responding to alarms
Issue 3.2 2014-12-10 Page 1-35
5. Spread a small amount of thermal compound (Nautel Part # HAG39, from the station
spares kit), thinly and evenly, on the bottom of the FET flange on the new PA PWB.
6. Secure the PA PWB on the module's heat sink using the six screws removed in Step 3 .
Ensure correct orientation (same as the adjacent PWB). Do not tighten the six screws at this
time.
7. Secure the FET (Q1) with two # 4 screws, a flat washer and a new split washer.
8. Using a torque screwdriver, tighten the screws to 6 inch pounds (0.672 Newton-meters).
9. Tighten the six PWB screws.
10. Solder the wires removed in Step 1 .
11. Return the RF power module to the transmitter (see “Installing an RF power module” on
page 1-29 ).
12. If you experience any reject load related alarms, it is possible that the replacement PA PWB
requires a change to its bias setting. A PA’s bias setting acts to balance the PA output power
levels based on different FET characteristics. If this occurs, perform the
“PA Biasing
Procedure” on page 1-36 .
NOTE:
You can damage the FET case if you fully tighten one screw while the other is loose. Try to
alternate tightening of the two screws to prevent this.