HP 83522A Service Notes page 231

Model 83522A
Service
front panel assemblies of the 8350A mainframe, where RPG pulses are decoded.
If multiple front panel functions are inoperative or erratic, the problem is most
likely a digital control problem. Detailed troubleshooting procedures for
checking front panel operation are provided in the Al/A2 service sheet. For
digital control problems, refer to the A3 Digital Interface service sheet, and
check the address, data, and control line outputs of the A3 assembly.
When there is a problem with a digital-to-analog interface (i.e. DAC), the
symptom is generally a discontinuity in the analog response.
Frequency Control
Troubleshooting a frequency control problem can be greatly simplified by first
defining the conditions under which the problem exists. When troubleshooting,
the R F Plug-in should be operating in the least complicated mode that exhibits
the frequency control problem. For instance, a CW frequency is less
complicated than a swept mode.
NOTE
To ensure accurate frequency counter readings, check for
adequate RF output power.
Incorrect Frequency Display after Instrument Preset. If the frequency
range displayed corresponds to the frequency range of another R F plug-in,
verify that Configuration Switch A3S1 is set correctly. Otherwise, there is a
digital problem.
Frequency Accuracy Problems. Frequency accuracy problems are most
likely related to the front panel FREQ CAL adjustment. Refer to Section I11 for
the FREQ CAL adjustment procedure. The YO DRIVE V on the A6 YO Driver
can be checked by comparing the rear panel lV/GHz output with frequency
selected and the actual RF output frequency. Connect a digital voltmeter to the
rear panel lV/GHz output. Compare the digital voltmeter indication with the
8350A FREQUENCY display and the actual RF OUTPUT frequency. If the
voltage corresponds to the actual output frequency, perform the Frequency
Accuracy adjustment in Section V before further troubleshooting.
Swept Frequency Accuracy Problem. A frequency accuracy problem that
occurs only during swept frequency modes is typically a delay compensation
problem. Refer to the A7 Marker for further troubleshooting.
Power Control
Power control problems normally fall into one of the following catagories.
No RF Output Power
Maximum Unleveled RF Output Power (no power control)
Excessive power variations
No RF Output Power. Remove the A4 ALC assembly; the RF OUTPUT
power should go to a maximum level. If not, the trouble is in the R F Section. If
the R F OUTPUT goes to maximum, the problem is in the A4 ALC assembly.