500 WATT RADIOBEACON TRANSMITTER
ND2000A-02x-xx0
Page 6-7
15 October 2004
Ensure hole in metal chassis and the chassis surface
under an insulating washer are free from burrs or
any sharp projection that could damage the
insulating washer.
(e) For power MOSFETs Q1 and Q3, position the
original (or an identical) insulating washer on
chassis where power MOSFET will be installed;
ensuring hole in insulating washer is aligned
with mounting hole in printed wiring board.
(f) Bend the ends of the leads of new power
MOSFET to fit into printed wiring board pads.
Ensure leads do not touch printed wiring pattern
at other than designated points.
(g) Install power MOSFET and secure using
hardware removed in step (b), noting the
cathode end of a diode is installed on the drain
terminal on the printed wiring board as depicted
in figure MD-11. Torque nuts to five inch-
pounds (0.57 Newton-meters or 0.58 kilogram-
meters).
(h) Perform a functional test as described in
paragraph 6.7.1.
(i) Solder anode lead of associated diode to source
terminal and the appropriate wires to the gate
and source terminals. Refer to wiring table
shown in figure MD-11 to determine identity of
wires connected to gate and source terminals.
6.8.2
POWER MOSFET REPLACEMENT
ON MODULATOR ASSEMBLIES:
Replace
defective power MOSFET Q1 on a modulator
assembly as follows: (Refer to figure MD-10 for
assembly detail).
(a) Disconnect or verify capacitor lead is
disconnected from source terminal.
(b) Remove nuts securing diodes CR1 and CR2 to
power MOSFET mounting hardware and
chassis mounted standoffs, and then carefully
lift off diodes.
(c) Loosen hardware securing pillar connected to
the source terminal.
(d) Unsolder gate, source and drain terminals from
printed wiring board, using a solder removal
system, and then remove power MOSFET.
Ensure solder is not splattered on chassis.
NOTE
There is an insulating washer between the metal
chassis and power MOSFET Q1. This insulator must
be retained for use when installing new power
MOSFET.
Ensure hole in metal chassis and the chassis surface
under insulating washer is free from burrs or any
sharp projection that could damage the insulating
washer.
(e) Bend the ends of the leads of new power
MOSFET to fit into printed wiring board pads.
Ensure leads do not touch printed wiring pattern
at other than designated points.
(f) Position the original (or an identical) insulating
washer on chassis where power MOSFET will
be installed; ensuring hole in insulating washer
is aligned with mounting hole in printed wiring
board.
(g) Install power MOSFET and secure using
hardware removed in step (b). Torque nuts to
five inch-pounds (0.57 Newton-meters or 0.58
kilogram-meters).
(h) Perform a functional test as described in
paragraph 6.7.2.
(i)
Solder lead of capacitor C2 to source terminal.
(j) Install diodes CR1 and CR2 using attaching
hardware removed in step (b). Ensure anode
end of both diodes is installed on device
mounting terminal.
(k) Tighten hardware securing pillar connected to
the source terminal.
