Fluke 5720A service manual Troubleshooting the Filter/PA Supply Assembly A18

5700A/5720A Series II Calibrator

Service Manual

DMM, measure the voltage at U9 pin 6 and verify it is the equal to the voltage at TP12 divided by 8 ±1%. If a failure is detected, check the HR8 resistor network, U9, and the associated components.

5-23. Troubleshooting the Filter/PA Supply Assembly (A18)

Proceed as follows to troubleshoot the Filter/PA Supply assembly (A18):

1.Place the Filter/PA Supply assembly on the extender card. Remove the Power Amplifier assembly (A16) and power up the Calibrator. Reference all measurements to PACOM (TP203). The Calibrator should be in its power-up default standby condition unless otherwise Noted.

2.Check the unregulated ±250V Supplies. Using a DMM, measure the dc voltage at the cathode of CR235 or CR239 and verify it is -280V±10%. Next, measure the dc voltage at the anode of CR208 or CR203 and verify it is +280V ±10%. Connect an oscilloscope to these points and verify the ripple is less than 5V p-p. If a failure is detected, check CR222, F202, F203, and associated components.

3.Check the unregulated ±500V Supplies. Using a DMM measure the dc voltage at TP209 and verify it is +565 ±10%. Next, measure the dc voltage at TP211 and verify it is -565 ±10%. Connect an oscilloscope to these points and verify the ripple is less than 5V p-p. If a failure is detected, check CR217, CR218, CR220, CR221, CR223, CR224, CR227, CR228, F201, F204, and associated components.

4.Check the Control Lines. Using a DMM, measure the dc voltage at TP205, TP207, and TP208. Verify they are all at +12V ±4V. Next measure the dc voltage at pins 13 and 14 of U201. Verify they are at- 12V ±4V. If a failure is detected, check Z201, U201A, U201B, and associated components.

5.Check the unregulated +250V Supply. Using a DMM, measure the dc voltage at TP210 and verify it is +280 ±10% If a failure is detected, measure the voltage at the cathode of VR211 and verify it is +140 ±20%. If this voltage is incorrect, check VR211, VR214, VR215, VR219, and Q208. If the voltage at the cathode of VR211 is correct then check Q201, CR201, CR203, CR208, CR210, and associated components.

6.Check the regulated +PA Supply at 0V. Using a DMM measure the dc voltage at TP201 and verify it is less than 1.0V. If a failure is detected, check Q207.

7.Check the regulated +PA Supply at +180V. Jumper TP207 to PACOM (TP203), measure the +PA Supply at TP201 and verify it is +190V±10%. If this voltage is correct, skip to step 8, otherwise continue as follows. Measure the output of the Current Limit circuit. Connect a DMM to pin 1 of U201 and verify it is -12±4V. If this voltage is incorrect, then the +PA Supply is current-limited. Check the output for shorts and check the current-limiting circuit contained in U201C, Q203, Q206, and associated components. If the voltage at pin 1 of U201 is correct, check Q205, Q202, VR212, VR207, and associated components.

8.Check the unregulated +PA Supply at +360V. Jumper TP207 and TP205 to PACOM (TP203), measure the voltage at TP210 and verify it is +480V±10%. If a failure is detected, check Q208, VR214, VR215, VR219, CR201, CR203, CR208, CR210, and associated components. Next, check the regulated +PA Supply at TP201 and verify it is +370V ±10%. If a failure is detected, check Q205 and VR216.

9.Check the Current Limiting of the +PA Supply. Jumper TP207 to PACOM (TP203)

and remove the jumper connecting TP205 to LO HI I (TP206). Connect an oscilloscope to the +PA Supply at TP201. Connect a 1 kΩ 10W resistor (such as Fluke P/N 157933) between PACOM (TP203) and the +PA supply output at Jumper

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