3808 A8: Zero Amp Hi Offset

Troubleshooting 5

Interpreting Diagnostic Fault Codes

3808 A8: Zero Amp Hi Offset

The Internal Cal Zero Amplifier circuit on the Switch Matrix assembly is tested for excessive offset 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 average value is over 0.155V. A failure indicates the Switch Matrix (A8) assembly is probably at fault.

3809 A8: Zero Amp Hi Gain Fault

The gain of the Internal Cal Zero Amplifier circuit in the high gain (130) 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 0.05V and then adjusted it until a null is achieved. The gain is tested to be 130 ±6%. A failure indicates the Switch Matrix (A8) assembly is probably at fault.

3810 A8: 2.2V Amp Noise Fault

3811 A8: Zero Amp Offset

3812 A8: 2.2V Gain Fault

3813 A8: 220mV Offset Fault

3814 A8: 220mV Divider Fault

3815 A8: 22mV Divider Fault

3816 Spare

This fault code is not used.

3817 Spare

This fault code is not used.

3818 A8: Out Lo To Sense Lo Continuity Fault

3819 A8: Relay Fault

A fault occurred while doing relay testing on the Switch Matrix assembly.

3820 Spare

This fault code is not used.

3821 Spare

This fault code is not used.

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Fluke 5720A 3808 A8 Zero Amp Hi Offset, 3809 A8 Zero Amp Hi Gain Fault, 3812 A8 2.2V Gain Fault 3813 A8 220mV Offset Fault