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5700A/5720A Series II Calibrator
Service Manual
5-22
3334 A9/A10: 1.9 Ohm Check Fault
The Current assembly (A7) outputs 13 mA which is routed through the Ohms Main
assembly (A10), via INT OUT HI, to the Ohms Cal assembly (A9) where it is connected
to the 1.9Ω resistance. The voltage drop across the 1.9Ω resistance is measured for 24.7
mV ±3% ±15 mV. A failure indicates the Ohms Cal assembly is probably at fault.
3335 A9/A10: Ohms Short Check Fault
The Current assembly (A7) outputs 130 mA which is routed through the Ohms Main
assembly (A10), via INT OUT HI, to the Ohms Cal assembly (A9) where it is connected
to the short. The voltage drop across the short is measured for 0V ±3% ±15 mV. A
failure indicates the Ohms Cal assembly is probably at fault.
3336 A9/A10: 2 Wire Compensation Fault
The two-wire compensation circuit is tested at its limits. The tests check to see if the
circuit can compensate for lead drops for the following currents and loads:
• 10 mA into 10Ω
• -10 mA into 10Ω
• 10 µA into 10 kΩ
• 5.6 µA into 19 kΩ
The Current assembly (A7) generates the desired current which is routed through the
Ohms Main assembly (A10), via INT OUT HI, to the Ohms Cal assembly (A9) where it
is connected to ACOM. The current into ACOM causes the 2 Wire Lead Drop
Compensation circuit to generate a voltage which is used in creating an equal current in
the opposite polarity for the current in ACOM. The voltage is measured on the DAC
assembly via the SDL line. The voltage expected from the compensation circuit is V = I
* -1000V/A. Failure of any of the tests indicates that the 2 Wire Lead Drop
Compensation circuit on the Ohms Cal assembly (A9) is probably at fault.
3337 A9/A10: Ohms Correction Factor Fault
The 13 volt reference on the DAC assembly is checked by the adc circuit on the DAC
assembly. A failure indicates the DAC assembly (A11) is probably at fault.
3338 Assembly A9 Not Responding
At power up the instrument checks to see what assemblies are not installed. This test
verifies that the Ohms Cal assembly is not responding. A failure indicates the Ohms Cal
assembly (A9) is probably at fault.
3339 A9: 8255 Was Reset
The control word of the 8255 on the Ohms Cal assembly is read. A failure indicates the
Ohms Cal assembly (A9) is probably at fault.
3340 A9/A10: 100 Ohm Cal Diag Fault
The 2/5/10V SOURCE circuit is set for 2V and connected across the 1 kΩ string on the
Ohms Main assembly. The resulting 0.2V across the 100Ω portion is connected to the -
input of the differential amplifier on the Ohms Cal assembly. The output of the DAC
assembly is set to 2V and connected across the 100 kΩ resistance in Z5 on the Ohms Cal