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A3 Assembly ADC Circuits
The ADC consists of a 12-bit DAC, 12-bit successive approximation register (SAR), data
multiplexers, and data latches. The ADC ASM (algorithmic state machine) controls the
ADC. Eight inputs are controlled by the ADC MUX. These include a positive peak detector,
negative peak detector, sampled video, scan ramp, YTO error voltage, FC MUX voltages, Cal
Oscillator tune voltage, and offset lock error voltage. A MUX on the Al4 frequency control
assembly selects which voltage is sent to the ADC MUX on the FC MUX signal line.
During NORMAL detector mode sweeps, when noise is detected by the rosenfell detector, the
ADC ASM automatically switches between POS PEAK and NEG PEAK.
ADC
Control
Signals
Refer to function blocks B and F of A3 Interface Assembly Schematic Diagram in the
HP 8560 E-Series Spectrum Analyzer Component Level Information.
The ADC requires two signals from the A2 controller assembly: HBADC-CLKO and
HBBKT-PULSE. HBBKT-PULSE
is used only in zero span. Use the following steps to verify
the signals.
1. Disconnect W22 from A2J8.
2. If a 10 MHz TTL signal is absent on W22, refer to the 10 MHz Reference (on the Al5 RF
assembly) troubleshooting procedure in Chapter 12, “RF Section.”
3. Set the spectrum analyzer
m
to zero.
4. Reconnect W22.
5. With an oscilloscope probe, monitor A3J401 pin 20.
6. If TTL pulses are absent, the A2 controller assembly is faulty. Refer to Chapter 10,
“Controller Section.” The presence of TTL pulses indicates a faulty A3 assembly.
7. Monitor A3J401 pin 23 (HBADC-CLKO). If a 1 MHz TTL clock signal is present,
HBADC-CLKO is working properly.
8. If HBKT-PULSE or HBADC-CLKO is missing, disconnect
A3Wl
from A2J2.
9. Monitor A2U5 pin 3 for HBKT-PULSE and A2U5 pin 7 for HBADC-CLKO.
10. If HBADC-CLKO is absent, troubleshoot the A2 controller assembly.
11. HBKT-PULSE is absent, refer to the information on troubleshooting the frequency
counter in Chapter 10, “Controller Section.”
12. Reconnect
A3Wl
to A2J2.
8-24
ADC/lnterface
Section