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Chapter 6 Service
Self-Test Procedures
4
6
618 - 625 System DAC failed
These tests use the internal ADC (U1701) to verify that the system DACs
are working correctly. There are eight system DACs. For each DAC, ADC
readings are taken at 25%, 50%, and 75% of full scale. The delta between
ADC readings are compared to the delta of DAC values to make sure the
DAC outputs scale proportionally to the inputs. A failure indicates a
malfunctioning system DAC(s), sysDac Mux channel(s) circuit, or ADC
Mux channel(s).
618: Contrast DAC
619: Leading Edge DAC
620: Trailing Edge DAC
621: Threshold DAC
622: Timebase Cal DAC
623: Offset DAC
624: Null DAC
625: Amplitude DAC
626 - 630 Relays failed
This test uses the internal ADC to test whether the output path relays,
hybrid amplifier, and output attenuators are working properly. First, the
straight through, no attenuator/amplifier, path is setup and an ADC
reading is taken. Each of the other attenuators and hybrid amplifier are
switched in, only one in the path at a time, and an ADC reading is taken
for each one. The gain of each path is given by the ratio of its ADC
reading to ADC reading of the straight through path.
A failure means that either the relay isn’t being properly switched or the
attenuator/amplifier isn’t providing the expected attenuation/gain.
626: Analog/Digital path selector
627: -10 dB attenuator path
628: -20 dB attenuator path
629: +20 dB amplifier path
630: Internal ADC overranged during one of the above tests
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