RADIOBEACON TRANSMITTER
ND500II (125 WATTS) DOUBLE SIDEBAND - NO VOICE
Page 6-3
15 September 2003
NOTE
It is not necessary to remove the adapter PWB or its
attaching hardware when replacing a power
MOSFET, unless the PWB has been damaged. Refer
to figure MD-12 for assembly/disassembly
information (mounting detail) for the power
MOSFETs and their adapter PWBs.
(b)
Remove and retain attaching hardware (6-32
nut, #6 Belleville washer, #6 flat washer, 6-32
screw and hexfet strap from power MOSFET
to be removed; noting nut, screw and flat
washer are brass.
NOTE
Q1 has an additional 0.187 spacer under its flat
washer. Q2, Q3, Q4 and Q5 have an additional flat
washer between the terminal lug and the PWB when
there is no PWB pad under the lug.
(c)
Carefully unsolder power MOSFET's leads
from the adapter PWB and lift away the power
MOSFET. Ensure solder is not splattered
across wiring patterns on PWB.
(d)
Inspect TO220 insulator which was under the
power MOSFET for obvious damage.
NOTE
It is recommended a new TO220 insulator be used
when a power MOSFET is replaced.
(e)
Insulate the centre lead of the replacement
power MOSFET using teflon tubing.
(f)
Position the replacement power MOSFET in
the appropriate position on the chassis. Ensure
an insulating sleeve is installed in the chassis
mounting hole and a TO220 insulator is
installed between the device and the chassis.
NOTE
It is recommended a new #6 Belleville washer be
used when a power MOSFET is replaced.
(g)
Install the power MOSFET's attaching
hardware using the mounting detail depicted in
figure MD-12 as a guide. Ensure device leads
are aligned with the appropriate wiring patterns
on the adapter PWB and tighten attaching
hardware finger tight.
NOTE
Q1 has a 0.187 spacer, which is installed between
the PWB and a terminal lug, on the nut side.
Q2, Q3, Q4 and Q5 have an additional flat, brass
washer; which is installed between the PWB and a
terminal lug, on the nut side; when there is no PWB
pad at the mounting hole.
Terminal lugs, which are secured by power
MOSFETs attaching hardware, are positioned
under the flat washer nearest the nut
The Belleville washer is positioned between the nut
and a flat washer.
(h)
Solder leads of replacement power MOSFET to
appropriate wiring patterns of adapter PWB.
Ensure there are no solder bridges between
patterns.
(i)
Complete installation by torquing attaching
hardware to 5.0 inch pounds (0.566 Newton
metres).
(j)
Perform a resistance measurement as detailed in
paragraph 6.5 to ensure replacement MOSFET
is serviceable.
(k)
Resolder any source lead which was removed
for testing to the source terminal of the
appropriate power MOSFET.
(l)
Resolder gate leads to gate terminals of power
MOSFETs that have been replaced.
NOTE
Power MOSFET Q1 has a ferrite bead positioned
over it's gate lead. Ensure ferrite bead is in place
before soldering lead to the gate terminal.
(m) Reinstall heat sink with the attaching hardware
removed in step (a).
