HP 8672S Operating And Service Manual page 97

Service
Models 8672S/86720A
SERVICE SHEET 1 (cont'd)
Test Equipment
Frequency Counter . HP 5343A
Power Meter. HP 436A
Power Sensor . HP 8481A
Spectrum Analyzer . HP 8569B
Diode Detector. HP 8472B
Digital Voltmeter . HP 3455A
Pulse Generator . HP 8013B
Oscilloscope . HP 1715A
FEU Power On Troubleshooting
Because the FEU power on troubleshooting re¬
quires that the Signal Generator System be disas¬
sembled, it should be performed only if power can¬
not be applied to the FEU or if it is determined that
the FEU is faulty. The FEU has three separate
power supplies. It is recommended that the out¬
puts of all three be checked in the following order:
NOTE
If any power supply requires adjust¬
ment, perform the adjustment procedure
for any assembly that uses the power
supply outputs.
a. Main power supply
A6TP1 +5 ±0.4 Vdc
A6TP2 +24 ±1.4 Vdc ^
b. ALC power supply
A9TP1 -10 ±0.8 Vdc
A9TP2 +20 ±0.7 Vdc
c. Pulse driver power supply
A1TP3 +12 ±0.7 Vdc
A1TP7 +5.2 ±0.4 Vdc
A1TP14 -12 ±0.7 Vdc
A1TP15 -5.2 ±0.4 Vdc
If any of the power supplies are out of tolerance,
refer to the applicable Service Sheet and correct
the problem before proceeding.
The following troubleshooting information is
based on the results of performing the Signal Gen¬
erator Operational Verification Check in Section
4. It assumes that the system has power applied to
it and is ready to operate. When the first malfunc¬
tion is encountered in the verification, refer to the
same check listed below for troubleshooting direc¬
tions. For example, if the first malfunction indica¬
tion occurs in the Power Check, refer to that check
in the troubleshhooting to determine the subse¬
quent corrective action. It is very important that
the applicable check be referenced at the first mal¬
function indication because the corrective action
assumes that all previous indications are correct.
Frequency Check Troubleshooting
1. If there is no output from the Signal Generator
System or if the frequency is incorrect, remove
the RF Input cable (W35) and check the output
from the Signal Generator. One of the following
three indications are possible:
a. No output from the Signal Generator.
b. Incorrect frequency from the Signal Gen¬
erator. In low band operation the output should
be from 4.21 to 6.2 GHz. In the high band the
frequency should be the same as that indicated
on the Signal Generator. If the Signal Genera¬
tor will not tune below 2 GHz, check that the
ground input (Nhet) from the FEU (pin 3 of Jl,
FROM 8672A ATTEN CONTROL) is present
and that the cable (W36) has continuity.
c. The output from the Signal Generator is
correct.
If a or b, troubleshoot the Signal Generator (refer
to the HP 8672A Operating and Service Manual).
If the ground (Nhet) is not present, refer to Service
Sheet 9. If c, continue with step 2.
NOTE
Always check the power supply voltages
in the FEU before troubleshooting any
individual circuit.
2. If the output from the Signal Generator is cor¬
rect, disassemble the Signal Generator System
and use a cable and adapters to connect the RF
OUTPUT from the Signal Generator to the
FEU.
NOTE
A good method of checking the low band
RF path and ALC loop is to set the FEU
to 0 dBm in pulse complement mode. In
this mode, the RF path can be broken
and measurements made without chang¬
ing the ALC levels.
8-16