HEWLETT PACKARD (HP) EPM-441A
Service Manual

Adjustments Power Reference Oscillator Level Adjustment

Equipment
Test power meter ................................... HP 432A Thermistor Mount ................................ HP 478A Option H75 Digital Voltmeter (DVM)....................... HP 3456A

Procedure
Note The procedure details the key presses required on the HP EPM-441A. For the HP EPM-442A the equivalent key presses should be performed on both channels. 1. Set up the DVM to measure resistance. Connect the DVM between the VRF connector on the rear panel of the HP 432A and pin 1 on the thermistor mount end of the sensor cable. Verify that no power is applied to the HP 478A 2. Round off the DVM reading to two decimal places and record this value as the internal bridge resistance (R) of the test power meter (approximately 200 �).
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R (Internal Bridge Resistance)_______________�

3. Connect the equipment as shown in Figure 3-3. The leads should be isolated from ground. Ensure that the power reference oscillator is off. Ensure that both the power meter under test and the HP 432A have been powered on for at least 30 minutes before proceeding to the next step. 4. Set the HP 432A range switch to coarse zero and adjust the front panel coarse zero control to obtain a zero meter indication. 5. Fine zero the HP 432A on the most sensitive range, then set the range switch to 1 mW. Note Ensure that the DVM input leads are isolated from chassis ground when performing the next step. 6. Set up the DVM to measure microvolts. 7. Connect the positive and negative input leads, respectively, to the Vcomp and VRF connectors on the rear panel of the HP 432A.

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HP EPM-441A/442A Service Guide