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Troubleshooting
Interpreting Diagnostic Fault Codes
5
5-17
3303 A9: 8255 Port C Fault
The diagnostics software reads port C of the 8255 IC on the Ohms Cal assembly (A9)
during the instruments dormant state. A failure indicates the Ohms Cal assembly (A9) is
probably at fault.
3304 A9: 10V Source Fault
The 2/5/10V SOURCE circuit on the Ohms Cal assembly (A9) is set for 10V and routed
to the adc circuit on the DAC assembly, via the SDL line, where it is measured for 10V
±7%. This 10V can be verified with a DMM, hi to TP13 and low to TP12. If the
measured voltage is out of tolerance, the 2/5/10V SOURCE circuit on the Ohms Cal
assembly (A9) is faulty. If the measured voltage is within tolerance, the diagnostic
circuit on the Ohms Cal assembly (A9) is probably at fault.
Note
If extender cards are available, verify that 10V SENSE LOis tied to SCOM.
This connection is done with relays onboth the Ohms assemblies.
3305 A9: 5V Source Fault
The 2/5/10V SOURCE circuit on the Ohms Cal assembly (A9) is set for 5V and routed
to the adc circuit on the DAC assembly, via the SDL line, where it is measured for 5V
±7%. A failure indicates the 2/5/10V SOURCE circuit on the Ohms Cal assembly (A9)
is probably at fault.
Note
If extender cards are available verify that 10V SENSE LOis tied to SCOM.
This connection is done with relays onboth the Ohms assemblies.
3306 A9: 2V Source Fault
The 2/5/10V SOURCE circuit on the Ohms Cal assembly (A9) is set for 2V and routed
to the adc circuit on the DAC assembly, via the SDL line, where it is measured for 2V
±7%. A failure indicates the 2/5/10V SOURCE circuit on the Ohms Cal assembly (A9)
is probably at fault.
Note
If extender cards are available verify that 10V SENSE LOis tied to SCOM.
This connection is done with relays onboth the Ohms assemblies.
3307 Spare
This fault code is not used.
3308 A9: Diff Amp Offset Fault
The offset of the Differential Amplifier circuit on the Ohms Cal assembly (A9) is
checked. The DAC output is set to 0V and connected to both the ±inputs of the
Differential Amplifier circuit. The output is routed to the adc circuit on the DAC
assembly via the RCL line. Ten reading are taken and this fault occurs of the difference
between the lowest and highest value if over 1 mV or if the absolute value is over