Agilent Technologies 34970A, Service Manual, Page: 173 / 273

622
Frequency counter failed
This test configures for the 100 mV ac
range. This test immediately follows test 621. With A4C301 holding
charge from test 621 the ac input is now switched to ground through
A4K103. This produces a positive pulse on the input to the frequency
comparator A4U310. While C301 discharges, the ENAB FREQ bit is
toggled four times to produce a frequency input to the counter logic in
A1U205. 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. The ADC is configured for 200 ms measurements.
The A1U205 pulse width modulated (PWM) DAC output (C224) is set
to about 4 volts. A reading is taken in with A4U101 in the MC state.
A second reading is taken in the PRE state. The precharge amplifier
voltage offset is calculated. The A1U205 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 is achievable.
624 Unable to sense line frequency
This test checks that the
LSENSE logic input to A1U205 is toggling. If no logic input is
detected, the meter will assume a 50 Hz line operation for all future
measurements.
625
I/O processor did not respond
This test checks that
communications can be established between
A1U205
and
A1U305
through the optically isolated (A1
U213
and
A1U214
) serial data link.
Failure to establish communication in either direction will generate
an error. If this condition is detected at power-on self-test, the
instrument will beep and the error annunciator will be on.
626 I/O processor failed self-test
A failure occurred when the earth
referenced processor, AU305, executed an internal RAM test.
6
Chapter 6 Service
Self-Test Procedures
171