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5-14 682XXB/683XXB MM
TROUBLESHOOTING
TROUBLESHOOTING TABLES
No Pulse Modulation of the RF Output
Description: The signal generator does not display any error messages
during self-test; however, there is no pulse modulation of the RF out
-
put.
Step 1. Set up the 682XXB/683XXB as follows:
a.
Press SYSTEM , then Reset .
b.
Press MODULATION , then Pulse to go to the Internal
Pulse Modulation Status display.
c.
Press On/Off to turn on pulse modulation.
Step 2. Using an oscilloscope, verify the presence of a TTL pulse
(with a pulse width of approximately 25 ns) at the rear panel
PULSE SYNC OUT connector.
If present, go to step 5.
If not present, go to step 3.
Step 3. Disconnect the cable, W129, from A6J4.
Step 4. Using an oscilloscope, verify the presence of the Pulse Sync
signal at A6J4.
If present, replace the cable W129.
If not present, replace the A6 PCB.
Step 5. Using a coaxial cable with BNC connectors, connect the rear
panel PULSE SYNC OUT connector to the External Trigger
Input on an oscilloscope and select External Trigger.
Step 6. Disconnect the cable, W122, from A6J6 and the cable, W123,
from A6J7.
Step 7. Using the oscilloscope, verify the presence of (1) a pulse train
at A6J7 (pulse signal to the Switched Filter) with an output
level of +2 volts to –2 volts, a pulse period of 1 ms, and a
pulse width of 200 ms; and (2) a pulse train at A6J6 (sample
and hold signal to the A10 ALC PCB) with an output level of
0 volts to +1 volt, a pulse period of 1 ms, and a pulse width of
200 ms.
Note that on an expanded timebase, the signal at A6J6 starts
approximately 50 ns before the signal at A6J7.
Table 5-4. Malfunctions Not Displaying an Error Message (3 of 6)