2-5
WARNING: DISCONNECT POWER PRIOR TO SERVICING
TABLE 2-1. RF POWER MODULE TROUBLESHOOTING
(Sheet 2 of 3)
SYMPTOM
CIRCUITRY TO CHECK
MOD PWM DRIVE INDICATOR
1. Refer to RF DRIVE INDICATOR
EXTINGUISHED AND FAULT
EXTINGUISHED OR FLICKERING OR FAULT
OR FUSE INDICATOR
INDICATOR ILLUMINATED in the preceding
ILLUMINATED
text and troubleshoot the power amplifier circuit
board.
2. If no defective circuitry is located on the power
amplifier circuit board, refer to FAULT OR FUSE
INDICATOR ILLUMINATED in the following
text and troubleshoot the modulator circuit
board.
MOD PWM DRIVE INDICATOR
1. Defective U2 or U13 on the modulator circuit board.
EXTINGUISHED
FAULT OR FUSE INDICATOR
1. Visually inspect regulator U10 for broken leads.
ILLUMINATED
2. Determine transistor reference voltages of a
modulator circuit board with no faults as
follows:
A. Remove a modulator with no 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 = 1.2V.
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 = .46V.
3. 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 modulator circuit board.
A. If the voltage is greater than
±
0.1 volt of
the reference, proceed as follows:
1. Remove the wire from terminal E1.
2. Using the voltmeter as described in the
preceding text, measure the drain-to-gate and
drain-to-source voltage of transistor Q1 on
the defective modulator circuit board.
B. If the voltage at Q1 is greater than
±
0.1V of
the reference, defective Q1.
C. If the voltage at Q1 is equal to the reference,
defective Q2.