Agilent Technologies 4284A Service Manual page 47

3-4. AFTER SERVICE PRODUCT SAFETY CHECKS
WHENEVER IT APPEARS LIKELY THAT PROTECTIVE SAFETY PROVISIONS
HAVE BEEN IMPAI RED, THE APPARATUS SHALL BE MARKED AS INOPERATIVE
AN D SHOULD BE SECURED AGAINST ANY UNINTENDED OPERATION.
PROTECTION PROVISIONS WILL HAVE LIKELY BEEN COMPROMISED I F, FOR
EXAMPLE:
INSTRUMENT SHOWS VISIBLE DAMAGE.
THE I NSTRU MENT FAILS TO PERFORM THE INTENDED M EAS U REMENT.
THE UNIT HAS UNDERGONE PROLONGED STORAGE UNDER UNFAVORABLE
CON DITIONS.
THE INSTRUM ENT WAS SEVERELY STRESSED I N TRANSPORT.
Perform the following five checks to verify the 4284A's safety (these checks may also be
used for safety checks after troubleshooting and repair).
1 . Visually inspect the interior of the instrument for any signs of abnormal internally
generated heat, such as discolored pri nted circuit boards and components,
damaged insu lation, or evidence of arcing. Determine the cause and repair.
2 . Use an ohmmeter which can accurately measure 0 .5
from the instrument enclosure to the power cord 's ground pin. The resistance
m ust be less than 0.5 O. Flex the power cord while making this measurement to
determine if any intermittent discontinuities exist.
3. Check the GUARD terminal on the front panel using the procedure outlined in step
2 .
4. U n plug the 4284A's power plug from t h e power source. Set t h e power switch to
O N . Tie the line and neutral pins of the power connector together and check the
resistance between them and the instrument's enclosure. The minimum acceptable
resistance is 2 MO. Find and replace any component which causes the instrument
to fail this test.
5. Verify that the correct fuse is installed.
0
3-2
THE
to check the resistance