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5700A/5720A Series II Calibrator
Service Manual
5-54
1 V
10 ms
F5-14.EPS
Figure 5-14. Waveform at TP13
8. Check the LOOP FILTER circuit. Power down the Calibrator, cut jumper E2 and
connect an external variable dc reference (2 to 12V) to TP11(common to TP18).
Power up the Calibrator and set it for 2V at 1 kHz. Connect a frequency counter to
TP13 and adjust the external dc reference so the frequency counter read less than 10
MHz (~9.8 MHz).Connect an oscilloscope to U20 pin 7 and verify it displays a
positive dc voltage. Next, change the dc reference so the frequency counter reads
greater than 10 MHz (~10.2 MHz). At this time U20 pin 7 should be a negative dc
voltage. If a failure is detected, check U20A, U20B, and associated components in
the LOOP FILTER circuit. Reconnect jumper E2 before continuing.
9. Check the 5-500K Divider. Connect a frequency counter to U21 pin 5. Set the
Calibrator to 2V at 1 MHz, 500 kHz, 200 kHz, 140 kHz, 100 kHz, and 50 kHz. At
each output frequency verify the frequency counter displays the same as selected
±0.01%. Next, connect the frequency counter to U21 pin 9. Set the Calibrator to 2V
at 2 kHz, 120 Hz, and 10 Hz. At each output frequency verify the frequency counter
displays the same as the selected ±0.01%. If a failure is detected, check U17 and
U21.
10. Check the Output Switching. Connect an oscilloscope and frequency counter to
TP16. Set the Calibrator for 2V at 1 kHz, operate, and verify the oscilloscope
displays a signal similar to Figure 5-15, and the frequency counter reads 1 kHz
±0.01%. Next, set the Calibrator for 2V at 100 kHz and verify the frequency counter
reads 100 kHz ±0.01%. If a failure is detected, check U18B, C, D, U15C, Q16, and
associated components.
5-9. Troubleshooting the Switch Matrix Assembly (A8)
Proceed as follows to troubleshoot the Switch Matrix assembly (A8):
1. The primary function of the Switch Matrix assembly is to connect the output from
the various assemblies within the Calibrator to the output binding posts via the
Motherboard relays. All relays on the Switch Matrix assembly are latching type.