Technical data

622 Frequency counter failed This test configures for the 100 mV ac
range. This test immediately follows test 621. With
C301 holding a
charge from test 621 the ac input is now switched to ground with
K103.
This produces a positive pulse on the input to the frequency comparator
U310A. While C301 discharges, the ENAB FREQ bit is toggled four times
to produce a frequency input to the counter logic in
U501. A failure
occurs if the counter can not measure the frequency input.
623 Cannot calibrate precharge This test configures to the 100 V dc
range with no input applied. The
ADC is configured for 200 ms
measurements. The
U500 pulse width modulated (PWM) DAC output
(
C512) is set to about 4 volts. A reading is taken in with U101 in the MC
state. A second reading is taken in the PRE state. The precharge
amplifier voltage offset is calculated. The
U500 DAC output is set to
about 1.5 volts and the precharge offset is measured again. The gain of
the offset adjustment is calculated. This test assures a precharge
amplifier offset adjustment is achievable.
624 Unable to sense line frequency This test checks that the
LSENSE
logic input to U500 is toggling. If no logic input is detected, the instrument
will assume 50 Hz line operation for all future measurements.
625 I/O processor does not respond This test checks that
communications can be established between
U500 and U700 through the
optically isolated (
U506 and U704) serial data link. Failure to establish
communication in either direction will generate an error.
626 I/O processor failed self-test This test causes the earth referenced
processor
U700 to execute an internal, ram test. Failure will generate
an error.
Chapter 6 Service
Self-Test Procedures
124