2-4
WARNING: DISCONNECT POWER PRIOR TO SERVICING
TABLE 2-1. RF POWER MODULE TROUBLESHOOTING
(Sheet 1 of 3)
SYMPTOM
CIRCUITRY TO CHECK
RF DRIVE INDICATOR
1. Determine transistor reference voltages of a
EXTINGUISHED OR FLICKERING
power amplifier with no faults as follows:
OR FAULT INDICATOR
A. Remove an operational power amplifier with no
ILLUMINATED
faults from an RF power module.
B. Using a digital voltmeter, operate the
voltmeter to diode check and determine a
reference voltage for the transistors on the
circuit board as follows:
1. Place the negative lead on the drain of Q1
(center pin) and the positive lead on the gate
and determine the voltage. The voltage using a
Fluke 77 meter = .45.
2. Place the negative lead on the drain of Q1
and the positive lead on the source and
determine the voltage. The voltage using a
Fluke 77 meter = .45.
2. Using the voltmeter as described in the preceding
step, measure the drain-to-gate and
drain-to-source voltage of transistor Q1 on the
defective power amplifier circuit board.
A. If the voltage is greater than
±
0.1 volt of
the reference, defective Q1, Q3, and Q5.
B. If the voltage is equal to the reference, repeat
the preceding step for transistor Q2 on
the defective power amplifier circuit board.
3. Using a digital voltmeter, operate the voltmeter
to diode check and troubleshoot transistor Q3 as
follows:
A. Place the negative lead on the drain of Q3
(center pin) and the positive lead on the gate
and determine if a short circuit condition is
present.
B. Place the negative lead on the drain of Q3
and the positive lead on the source and
determine if a short circuit condition is
present.
C. If a short circuit condition is present, defective
Q3.
4. Repeat the procedure for transistors Q4, Q5, and
Q6.
5. Visually inspect regulator U1 for broken leads.
6. Check and replace all blown fuses on the circuit
board.
