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5700A/5720A Series II Calibrator
Service Manual
5-34
3801 A8: 8255 Port A Fault
The diagnostics software writes and reads to port A of the 8255 IC on the Switch Matrix
assembly. A failure indicates the Switch Matrix assembly (A8) is probably at fault.
3802 A8: 8255 Port B Fault
The diagnostics software reads port B of the 8255 IC on the Switch Matrix assembly. A
failure indicates the Switch Matrix assembly (A8) is probably at fault.
3803 A8: 8255 Port C Fault
The diagnostics software reads port C of the 8255 IC on the Switch Matrix assembly. A
failure indicates the Switch Matrix assembly (A8) is probably at fault.
3804 A8: Zero Amp Lo Noise Fault
The Internal Cal Zero Amplifier circuit on the Switch Matrix assembly is tested for noise
in the low gain configuration. This is done by connecting the circuit input to RCOM, by
turning on Q7, and connecting the output to the RCL line where it is measured by the adc
circuit on the DAC assembly. The adc circuit takes ten readings and this failure occurs if
the difference between the lowest value and highest value of the ten readings is over
0.0001V. A failure indicates the Switch Matrix assembly (A8) is probably at fault.
3805 A8: Zero Amp Lo Offset
The Internal Cal Zero Amplifier circuit on the Switch Matrix assembly is tested for
excessive offset in the low gain configuration. This is done by connecting the circuit
input to RCOM, by turning on Q7, and connecting the output to the RCL line where it is
measured by the adc circuit on the DAC assembly. The adc circuit takes ten readings and
this failure occurs if the average value is over 0.035V. A failure indicates the Switch
Matrix (A8) assembly is probably at fault.
3806 A8: Zero Amp Lo Gain Fault
The gain of the Internal Cal Zero Amplifier circuit in the low gain (10) configuration is
tested. The circuit input is connected to the output of the DAC assembly and the circuit
output is connected to the RCL line. The RCL line is connected to the +input of the adc
circuit and the -input is connected to the 6.5V reference. The gain of the Internal Cal
Zero Amplifier is determined by setting the DAC output to the nominal 0.65V and then
adjusted it until a null is achieved. The gain is tested to be 10 ±6%. A failure indicates
the Switch Matrix (A8) assembly is probably at fault.
3807 A8: Zero Amp Hi Noise Fault
The Internal Cal Zero Amplifier circuit on the Switch Matrix assembly is tested for noise
in the high gain configuration. This is done by connecting the circuit input to RCOM, by
turning on Q7, and connecting the output to the RCL line where it is measured by the adc
circuit on the DAC assembly. The adc circuit takes ten readings and this failure occurs if
the difference between the lowest value and highest value of the ten readings is over
0.0015V. A failure indicates the Switch Matrix (A8) assembly is probably at fault.