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Chapter 2 Service
Pre-Troubleshooting Information
Assembly-Level Service Guide 2-39
2
After Service Considerations
Product Safety Checks
The following safety checks must be performed after any troubleshooting
and repair procedures have been completed to ensure the safe operation of
the instrument.
WARNING RESISTANCE CHECKS DESCRIBED IN THE FOLLOWING TEXT
REQUIRE THAT THE POWER CORD BE CONNECTED TO THE
INSTRUMENT AND THAT AC POWER BE DISCONNECTED.
BE SURE THAT THE POWER CORD IS NOT CONNECTED TO
POWER BEFORE PERFORMING ANY SAFETY CHECKS.
1 VISUAL INSPECTION. Visually inspect the interior of the instrument for
any signs of abnormal internally generated heat, such as discolored
printed circuit boards or components, damaged insulation, or evidence of
arcing. Determine and remedy the cause of any such condition.
2 GROUND CONTINUITY TEST. Plug the power cord into the rear-panel
power receptacle. (DO NOT connect the instrument to ac power at this
time.) Using a suitable ohmmeter, check resistance from the instrument’s
metallic connection (such as the rear panel or BNC ground collar) to the
ground pin on the power cord plug. The reading must be less that 1
Ω
.
Flex the power cord while making this measurement to determine
whether intermittent discontinuities exist.
3 Check any indicated front- or rear-panel ground terminals marked, using
the above procedure.
4 INSULATION RESISTANCE TEST. Tie the line and neutral pins of the
power cord plug together. Measure the resistance from the instrument
enclosure (chassis) to the line and neutral pins of the power cord plug.
The minimum acceptable resistance is 2 M
Ω
. Replace any component
which results in a failure.
Product Performance Checks
After replacement of any assembly or module, perform the operational
verification test in Chapter 1, “Performance Tests,” of this guide.