they walk across the carpet. This static
charge will eventually have to be dis-
charged. Discharging to the MOSFET
could damage the MOSFET.
NOTE
MOSFET transistors which are in circuit
in the GATES Series™ transmitters are
immune to this damage.
The MOSFET transistors are shipped in
antistatic packaging. The transistors should
remain in this packaging until they are to be
used or tested.
B.5.
Testing MOSFET’s
The MOSFET’s used in the GATES Se-
ries™ transmitters may be checked with an
ohmmeter. However there is a requirement
which restricts the use of some ohmmeters.
If the battery voltage is too low (under 3V)
or too high (over 20V) the ohmmeter cannot
be used. A battery voltage less than 3V will
not give an operational check of the transis-
tor and a battery voltage greater than 20V
may result in damage to the transistor under
test. A Simpson 260, which uses a 9V bat-
tery on the Rx10k scale works quite well.
The following test applies to all MOS-
FET’s used in the transmitter, but is not
necessarily applicable to MOSFET’s used
in other equipment.
This test will show how a MOSFET can
be switched “on” and “off” by charging and
discharging the gate of the MOSFET.
Refer to Figure B-2 for the following test.
Connect the positive lead of the ohmmeter
to the source of the transistor. Momentarily
connect the negative lead to the gate and
then connect it to the source. Then connect
the positive lead to the drain. The ohmmeter
should read at least 2 megohms.
Remove the positive lead from the drain
and momentarily touch it to the gate. Re-
connect the positive lead to the drain. The
ohmmeter should read very near zero ohms.
CAUTION
IF THE TRANSISTORS IN THE IPA REQUIRE
CHANGING, ENSURE THAT ALL OF THE
TRANSISTORS ARE OF THE SAME TYPE
NUMBER AND ARE FROM THE SAME MANU-
FACTURER.
Figure B-2. Outline of MOSFET
Figure B-1
Upper Trace - Q12 or Q13, 60-120Vp-p
Lower Trace - IPA input, 15-25Vp-p
B-2
888-2314-001
Rev. AE 03-05-2002
WARNING: Disconnect primary power prior to servicing.
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