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5700A/5720A Series II Calibrator
Service Manual
5-58
Note
The connection from the test points to the resistance values is through
latching type relays for all resistances except 10M, 19M, and 100 M
Ω
values. These relays are put in the set or reset position and remain in that
position even after power has been removed. To troubleshoot the path
through the relays, simply set the Calibrator to the function in which a
problem is detected and then turn off the Calibrator. The relays remain in
either the set or reset position. Check individual relays by connecting an
external power supply (a typical 9V battery works well) across the set coil
to place the relay in the set position or the reset coil to place the relay in
the reset position.
3. Repeat step 2 for the resistances in Table 5-2 and verify they are within the specified
tolerance.
Table 5-2. Ohms Main Resistance Tolerance
Resistance Tolerance
19Ω +/-0.07%
100Ω +/-0.03%
190Ω +/-0.03%
1 kΩ +/-0.03%
1.9 kΩ +/-0.03%
4. Check the 100 MΩ resistance. Set up the ohmmeter for a two wire resistance
measurement and connect IN HI to TP4 and IN LO to TP3. Set the Calibrator to 100
MΩ, operate, INT SNS, and verify the ohmmeter reads 100 MΩ ±5.0%. If a failure
is detected, check relay K5 and90.
5-13. Troubleshooting the DAC Assembly (A11)
Proceed as follows to troubleshoot the DAC assembly (A11):
1. Remove the front and back shields and place the DAC assembly on the extender
card. Power up the Calibrator.
2. Check the 13V reference. Connect DMM to TP2 (common to TP3). The voltage
should be between +13 and +14V and very stable. (Some drift may be seen while the
assembly is warming up.) If the 13V reference is faulty, check the power supply
voltages to the HR5 Reference Hybrid. If all the supplies are correct, the HR5
Reference Hybrid is probably at fault.
3. Check CH1 SHUNT. Connect an oscilloscope probe to TP6 (with common
connected to TP3). Set the oscilloscope to 2V/div at 2 ms/div and verify it displays
pulses as shown in Figure 5-17. If the displayed signal is incorrect, skip to Duty
Cycle Control Circuit.
4. Check CH1 SERIES B. Connect an oscilloscope to TP4 (common to TP3).Set the
oscilloscope to 10V/div at 2 ms/div and verify it displays pulses as shown in Figure
5-18. Next, set the Calibrator to 6.5V dc, operate. Verify the oscilloscope displays
pulses with approximately 50% duty cycle as shown in Figure 5-19. If either of these
displayed signals are incorrect, skip to Duty Cycle Control Circuit.