Power Sweep Not Functioning Properly; No Power Output - HP 8560A Service Manual

Power Sweep Not Functioning Properly

Power sweep is accomplished by stepping Real Time Dac #l (R/T DACl) which adds an
offset to the POWER LVL signal. Refer to Function Block S of Al4 Frequency Control
Assembly schematic. R/T DACl is an 8-bit dac and can provide power sweeps of up to
12.8 dB. This is equivalent to 0.05 dB per dac step. Since R/T DACl has only 256 discrete
settings but 601 points per sweep are digitized, up to three adjacent points per sweep may
correspond to the same power level setting.
1. If the power sweep appears to be non-monotonic, the fault probably lies on the A3
Interface Assembly (Real Time DACs). To check the operation of R/T DACl, monitor
the BLANKING output of the HP 8560A. Set the POWER SWEEP RANGE to 12.8 dB
and TRK GEN RF POWER to -10 dBm. Set the HP 8560A SWEEPTIME to 50 ms. A 0
to +lO V ramp should be observed on the oscilloscope. The amplitude of the ramp should
decrease approximately 780 mV for each 1 dB decrease in POWER SWEEP RANGE.
Note
Although POWER SWEEP RANGE may be set to a 12.8 dB sweep width,
the POWER SWEEP function is only warranted to have a 10 dB sweep width.
2. Perform the Vernier Accuracy Performance Test. If this test fails, refer to Vernier Accuracy
Out-of-Tolerance, above.

No Power Output

The A10 requires power supplies, a 1st LO signal, and a 600 MHz drive signal in order to
provide power output.
1. Check power supplies on A14J13 and AlOJl. Refer to the Al4 Frequency Control
Assembly schematic.
2. Verify that the voltage at A14J17 pin 14 is greater than +14 Vdc. If the voltage is not
greater than +14 Vdc, troubleshoot A14.
3. Check that ALC-EXT, measured at A17J13 pin 10, is at a TTL low when the TG is set to
ALC INT and at a TTL high when the TG is set to ALC EXT.
4. Check that the 600 MHz drive signal is -8 dBm +/-3.5 dB. If the signal is outside of this
range, troubleshoot the Al5 RF Board Assembly.
5. Check that the 1st LO input signal is +16 dBm f2 dB. Perform the 1ST LO OUTPUT
Amplitude test, measuring instead at the end of W43 nearest AlO.
6. Check the tracking adjustment controls. Monitor A14J16 pin 13 with a DVM. On the
HP 8560A, use the STEP keys and numeric keypad to set the COARSE TRACK ADJ
value from 0 to 255. The voltage measured should increase from 0 V to +lOV.
Monitor A14J17 pin 13 with the DVM. Use the RPG knob to set the FINE TRACK ADJ
value from 0 to 255. The voltage measured should increase from 0 V to +lOV.
Monitor A14J17 pin 15 with the DVM. The voltage at this point should change as both the
FINE TRACK ADJ and COARSE TRACK ADJ values are changed, however the voltage
change per step of the FINE TRACK ADJ will be much less (about one-sixtieth) than the
voltage change per step of the COARSE TRACK ADJ.
RF Section 11-23