Keysight Technologies E8257D Service Manual page 87

Troubleshooting
Troubleshooting Assembly–Level Problems
3. The voltage measured by the DVM should be approximately −1.8 V. If it is
4. If pulse modulation is working, perform the A8 Output self–test.
1206 20 GHz IQ Modulator
1. If the power supplies +8V AF, +2.5V AF, +9V AFSW, +12V AFSW, +15V
2. If the VD724 Doubler, test index 6, fails, replace the A35 I/Q Modulator.
3. If self–test TC672RF indexes 8, 9, 11, or 12 fail:
E8257D/67D, E8663D PSG Signal Generators Service Guide
not, use an oscilloscope to view P131–6 of the A31 Motherboard (this is
the pulse signal out of the A11 Pulse/Analog Modulation Generator).
Change the pulse period to 1 ms and the pulse width to 500 μs.
— If the pulse is not present, perform the A11 Pulse/Analog
Modulation Generator self–test, and follow the troubleshooting
procedure.
— If the self–test passes, refer to
page 122, and check the lowband (<3.2 GHz) path.
— If the self–test fails, refer to the A8 Output test troubleshooting.
VLIMF, or −15VSWBIAS fail, refer to the table
supplies used by the A35 I/Q Modulator as they leave the A26 MID
connector.
— If the signals are good at the A26 MID connector, replace the A35
I/Q Modulator.
a. Remove the cable from J2 of the A29 20 GHz Doubler.
b. While measuring the signal at J2 with a spectrum analyzer, run
self–test 1206. You should see a +20 dBm signal at 5 GHz.
— If the signal is bad, troubleshoot the RF path.
— If the signal is good and TC672RF indexes 8, 11, or 12 have
failed, replace the A35 I/Q Modulator.
— If the signal is good and TC672RF index 9 has failed, you must
also check the I/Q signals from the A13 I/Q Multiplexer:
1. Remove the cable from J6 (I) of the A35 I/Q
2. Execute a single 1206 self–test. The signal on the
3. If the signal is good, reconnect the cable to J6,
"Troubleshooting the RF Path" on
Modulator, and connect it to an oscilloscope.
oscilloscope should pulse to approximately −0.5 Vdc
for approximately 500 ms.
— If the signal is bad, refer to the A13 I/Q
Multiplexer troubleshooting.
remove the cable to J7 (Q), and connect this cable
to the oscilloscope.
page 83, and check the
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