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5700A/5720A Series II Calibrator
Service Manual
5-8
2815 A11: 6.5V Reference Fault
The DAC’s 6.5V reference (REF6) is connected to the -input of the adc circuit and the
DAC output (DAC SENSE CAL) is connected to the +input. The 6.5V reference is
measure by adjusting the DAC until a null is achieved. This fault occurs if the 6.5V
reference is over 10% of the nominal. A failure indicates the DAC assembly (A11) is
probably at fault.
2816 A11: 13V Buffered Reference Fault
The DAC’s 13V buffered reference (BRF13 and BSRF13) is connected to the -input of
the adc circuit and the DAC output (DAC SENSE CAL) is connected to the +input. The
13V buffered reference is measure by adjusting the DAC until a null is achieved. This
fault occurs if the 13V buffered reference is over 10% of the nominal. A failure indicates
the DAC assembly (A11) is probably at fault.
2817 A11: 13V Reference Fault
The DAC’s 13V reference (REF13) is connected to the -input of the adc circuit and the
DAC output (DAC SENSE CAL) is connected to the +input. The 13V reference is
measure by adjusting the DAC until a null is achieved. This fault occurs if the 13V
reference is over 10% of the nominal. A failure indicates the DAC assembly (A11) is
probably at fault.
2818 Assembly A11 Missing
At power up the instrument checks to see what assemblies are not installed. This test
verifies that the DAC assembly is not responding. A failure indicates the DAC assembly
(A11) is probably at fault.
2819 A11: 8255 Was Reset
The control word of the 8255 on the DAC assembly is read. A failure indicates the DAC
assembly (A11) is probably at fault.
2820 A11: Fine Adjust Channel Fault
The second channel of the DAC assembly is tested. The second channel is set to a count
which gives 0V at the DAC output. The output is measured by the adc circuit. The
second channel count is increased and the increase in the DAC output is verified. A
failure indicates the DAC assembly (A11) is probably at fault.
2821 A8/A11: +11/22V DC Zero Estimate Fault
The DAC is in either the +11V or +22V range. Its output (DAC SENSE CAL) is
connected to the +input of the adc circuit and the -input of the adc circuit is connected to
RCOM. The zero is estimated by adjusting the DAC until a null is achieved. This fault
occurs when the nulling process does not converge. A failure indicates the DAC
assembly (A11) is probably at fault.