Fluke 5720A 2822 A8/A11 -11/22V DC Zero Estimate Fault, 2825 A11 Couldn’t Est 6.5V Or 13V Buf Ref

Troubleshooting 5

Interpreting Diagnostic Fault Codes

2822 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 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 (A11) assembly is probably at fault.

2823 A11: Couldn’t Estimate +11V Or 22V Gain

One of the DAC’s references is connected to the -input of the adc circuit and DAC output (DAC SENSE CAL) is connected to the +input. The gain 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 (A11) assembly is probably at fault.

2824 A11: Couldn’t Estimate 6.5 MHz Or 13 MHz Ref

One of the DAC’s references is connected to the -input of the adc circuit and DAC output (DAC SENSE CAL) is connected to the +input. The reference 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.

2825 A11: Couldn’t Est 6.5V Or 13V Buf Ref

One of the DAC’s buffered references is connected to the -input of the adc circuit and DAC output (DAC SENSE CAL) is connected to the +input. The buffered reference 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 (A11) assembly is probably at fault.

2826 A11: A/D Overload Fault

The adc on the DAC assembly is tested by putting a positive overload then a negative overload into the adc input. The adc output is read and compared against an expected overload reading for both the positive and negative overload. If either of these tests fail the fault message is sent. A failure on either of these tests indicates that the DAC assembly (A11) is at fault.

3100 A14: 8255 Control Word

The diagnostics software read the control word of the 8255 IC on the High Voltage Control assembly. A failure indicates the High Voltage Control assembly (A14) is probably at fault.

3101 A14: 8255 Port a Fault

The diagnostics software writes and reads data to port A of the 8255 IC on the High Voltage Control assembly. A failure indicates the High Voltage Control assembly (A14) is probably at fault.

3102 A14: 8255 Port B Fault

The diagnostics software reads port B of the 8255 IC on the High Voltage Control assembly. A failure indicates the High Voltage Control assembly (A14) is probably at fault.

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