Specifications

1. If the LED still does not light, check F3 and F4.
2. If the fuse(s) are open, check for a shorted T1, T2, C11
or C12.
b. If the fuses are not open:
1. Verify the presence of RF drive on the RF Amplifier.
Refer to Section VI, Troubleshooting paragraph title
“Measuring RF Drive.”
2. It should be 22 to 25 Volts p-p with a negativeDC offset.
3. If the RF Drive waveform has no DC offset (is centered
on the 0VDC axis) that side is on, check Q9 and Q10
and DS3 for a short.
WARNING
ENSURE THAT THE TRANSMITTER IS TURNED OFF AND ALL
PRIMARY POWER IS TURNED OFF AT THE WALL DISCONNECT
SWITCH BEFORE OPENING ANY DOOR OR PANEL. BEFORE
REMOVING PANELS OR OPENING DOORS, VERIFY THAT THE
RF AMP POWER SUPPLY IS DISCHARGED BY CHECKING
“PA+VDC” ON THE FRONT PANEL MULTIMETER. USE A VOLT-
METER TO VERIFY THE POWER SUPPLIES HAVE BEEN DIS-
CHARGED PRIOR TO TOUCHING ANY COMPONENTS.
4. If the signal on CR3 and/or CR4 is negative, turn off the
transmitter and remove the module.
5. Using an Ohmmeter check Q15, Q17, Q13, Q11, Q9 for
side A and Q10, Q12, Q14, Q18, and Q16 for side B.
G.7.2
DS3 Illuminated
This is a normal condition when the step should be turned on.
a. If the LED will not extinguish when the module should be
turned off:
1. Turn off the transmitter and remove the module.
2. Using an Ohmmeter check Q15, Q17, Q13, Q11, Q9 for
side A and Q10, Q12, Q14, Q18,and Q16 for side B.
G.7.3
DS1 Illuminated RED
If DS1 is illuminated, this indicates that F1 is open and that the
MOSFETs Q1, Q3, Q5, and/or Q7 may have failed.
a. Remove the module from the transmitter and ohmmeter
check the transistors using the Testing MOSFETs steps in
the Maintenance part of this section.
b. If a single MOSFET in a pair is found to have failed
(Example Q3 shorted Q1 okay), the entire set of 4 MOS-
FETs should be replaced.
G.7.4
DS2 Illuminated RED
If DS2 is illuminated this indicates that F2 is open and that the
MOSFET’s Q2, Q4, Q6, and/or Q8 may have failed.
a. Remove the module from the transmitter and ohmmeter
check the transistors using the Testing MOSFETs steps in
the Maintenance part of this section.
b. If a single MOSFET in a pair is found to have failed
(Example Q2 shorted Q4 okay), the entire set of 4 MOS-
FETs should be replaced.
G.7.5
Excessive Drive Phase Difference
a. Measure the drive phase on the RF Ampifier using the
procedure provided in Section V.
b. If a module is out of specifications on drive phasing, first
substitute a new module.
c. If the module is the problem it is most likely caused by:
1. A defective drive transformer, T1 or T2 or
2. A defective MOSFET, or associated circuitry.
d. If a module has just been repaired, check the ON/OFF
components, such as transistors and diodes. A poor solder
P1-50
P1-50 (RFA OFF)
888-2339-002 G-7
WARNING: Disconnect primary power prior to servicing.