HP 8753E - Al4 Divide-By-N Circuit Check

Al4 Divide-by-N Circuit Check
Note
The Al3 assembly should still be out of the instrument and the
Al4 assembly on an extender board.
1. Ground A14TP14 and confirm (as in the Al4 VCO Exercise) that the VCO
oscillates at approximately 50 to 55 MHz.
2. Put the analyzer in CW mode (to avoid relock transitions) and activate the
F’RACN TUNE service mode.
3. Connect an oscilloscope to A14J3 and observe the output.
4. With the F’RACN TUNE service feature, vary the frequency from 30 MHz to
60.8 MHz.
5. The period of the observed signal should vary from 5.5 ps to 11 p.s.
q If this procedure produces unexpected results, the Al4 assembly is faulty.
q If this procedure produces the expected results, perform the “A14-to-Al3
Digital Control Signals Check. n.
6. Remember to replace the Al3 assembly.
A14-to-Al3 Digital Control Signals Check.
The Al4 assembly generates a ‘ITL cycle start (CST) signal every 10
microseconds. If the VCO is oscillating and the CST signal is not detectable at
A14TP3, the Al4 assembly is non-functional.
Use the CST signal as an external trigger for the oscilloscope and monitor the
signals in ‘Ihble 7-6. Since these ‘ITL signals are generated by Al4 to control
A13, check them at Al3 6rst. Place Al3 on the large extender board. The
signals should look similar to Pigure 7-21. If these signals are good, the Al3
assembly is defective.
Source Troubleshooting 7-28