E8257D/67D, E8663D PSG Signal Generators Service Guide 87
Troubleshooting
Troubleshooting Assembly–Level Problems
3. The voltage measured by the DVM should be approximately −1.8 V. If it is
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.
4. If pulse modulation is working, perform the A8 Output self–test.
— If the self–test passes, refer to “Troubleshooting the RF Path” on
page 122, and check the lowband (<3.2 GHz) path.
— If the self–test fails, refer to the A8 Output test troubleshooting.
1206 20 GHz IQ Modulator
1. If the power supplies +8V AF, +2.5V AF, +9V AFSW, +12V AFSW, +15V
VLIMF, or −15VSWBIAS fail, refer to the table page 83, and check the
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.
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:
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
Modulator, and connect it to an oscilloscope.
2. Execute a single 1206 self–test. The signal on the
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.
3. If the signal is good, reconnect the cable to J6,
remove the cable to J7 (Q), and connect this cable
to the oscilloscope.
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