HP 83522A Service Notes page 256

Service Model 83522A
Sweep Circuitry
A failure in the sweep circuitry may cause the YIG to sweep between improper
frequency endpoints, or, not sweep at all. If the YO Drive Voltage is missing, the
instrument may toggle between two or more CW frequencies.
1. Check the YO DRIVE V (TP14) for the waveform shown in Figure 8-46. If
this waveform is correct, then the Sweep and Interrupt circuits are working
properly, and troubleshooting should continue with the YO Current Driver
section below.
a. If YO DRIVE V is incorrect, check BVTUNE (TP4) for the waveform
shown in Figure 8-50. If it is missing or of the wrong amplitude, trace
the problem back through the inputs of U10 (both should be close to
0 Vdc) to the sweep ramp output of the 8350A.
b. If the waveform at TP14 appeared to be level-shifted, check
-
10 VREF
(TP3) for -10 Vdc +1 mV. Then, with the plug-in sweeping its entire
range, check OFFSET (TP2) for approximately +9 Volts. If this signal
is incorrect, select a CW frequency of 2.4 GHz and press
SHIFT 5
2 .
Check TP2 for a +0.4 to +9.2 Volt pulse. If this fails, check
address decoding and the DAC latches using the Digital Control
troubleshooting procedure described below.
2.
If BVTUNE is correct, check SCVTUNE (TPI) against the waveform
shown in Figure 8-50. If it appears to be bad, run the Scale DAC Test by
setting a CW frequency of 8.4 GHz and pressing
SHIFT
5
2 . Check
that U9 pin 17 is at -10 Vdc. Then check TP1 for the waveform shown in
Figure 8-53. If this fails, check address decoding and the DAC latches using
the Digital Control troubleshooting below.
3. Check +20V FREQ REF (TP13) for +20 Vdc f 10 mV. If it is not, trace the
supply voltage back to the 8350A. Then check that SUPPLY VOLTAGE
CORRECTION (TP15) is at approximately -1 1.4 Vdc. If it is not,
troubleshoot U11.
4. Finally, check that the summing junction, U16 pin 2, is at 0 Vdc. If it is not,
troubleshoot U16.
YO Drive Circuits
1. Check +20V FREQ REF at TP13 for +20V k10 mV. If it is not,
troubleshoot back to the mainframe supply.
The circuitry surrounding U24 and A9Q1 is responsible for converting the YO
DRIVE V to a drive current for the YO coil. A failure here will usually result in
gross frequency errors.
2. Press
INSTR PRESET
to sweep the entire range of the plug-in. Check
TP12 for the waveform shown in Figure 8-48. This represents the voltage
(not the current) across the YO'S main coil, and will give an indication as to
whether current is passing through the coil. If this waveform is correct,
suspect the YIG oscillator. Refer to the RF Section Service Sheet.