500 WATT RADIOBEACON TRANSMITTER
ND2000A-02x-xx0
Page 6-8
15 October 2004
6.8.3
POWER MOSFET REPLACEMENT
ON RF DRIVE AMPLIFIER ASSEMBLIES
:
Replace defective power MOSFET(s) on a RF drive
amplifier assembly as follows: (Refer to figure MD-
21 for assembly detail).
(a) Remove hardware securing the power MOSFET
to the chassis.
NOTE
There is an insulating washer and an insulating pad
between the metal chassis and power MOSFET Q1.
These insulators must be retained for use when
installing new power MOSFET.
(b) Loosen hardware securing the adapter PWB to
the chassis.
(c) Unsolder gate, source and drain terminals from
the adapter PWB, using a solder removal system
and then remove power MOSFET. Ensure
solder is not splattered on the chassis or between
the pads on the adapter PWB.
(d) Remove and retain the insulating sleeve on the
drain terminal of the power MOSFET just
removed.
Ensure hole in metal chassis surface under an
insulating washer and an insulating pad is free from
burrs or any sharp projection that could damage the
insulating washing or insulating pad.
(e) Secure hardware securing the adapter PWB to
the chassis.
(f) Measure, using an ohmmeter, resistance
between each of the adapter PWB's three printed
wiring terminals and ground. Resistance
measured should be an open circuit for each
situation.
(g) If the resistance measured in step (f) is not an
open circuit, adjust the position of the adapter
PWB to obtain an open circuit between all three
terminals and ground.
(h) For power MOSFET Q1, 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 on the metal chassis.
(i) Install power MOSFET using hardware
removed in step (a). Do not fully tighten the
hardware.
(j) Solder the gate and source leads to the
appropriate adapter PWB terminals. Trim the
power MOSFET's leads to prevent shorting to
the drain terminal.
(k) Install the insulating sleeve removed in step (d)
to the drain lead on the power MOSFET.
(l) Loosen hardware securing the adapter PWB to
the chassis.
(m) Solder the drain lead to the appropriate adapter
PWB terminal.
(n) Torque hardware to five inch-pounds (0.57
Newton-meters or 0.58 kilogram-meters).
(o) Perform a function test as described in
paragraph 6.7.3.
6.8.4
POWER MOSFET REPLACEMENT
ON DC-DC CONVERTER ASSEMBLIES:
Replace defective power MOSFET on a dc-dc
converter assembly as follows: (Refer to figure MD-
27 for assembly detail)
(a) Remove hardware securing the power MOSFET
to the chassis.
NOTE
There is an insulating washer and an insulating pad
between the metal chassis and power MOSFET.
These insulators must be retained for use when
installing new power MOSFET.
(b) Loosen hardware securing the adapter PWB to
the chassis.
