Instruction manual

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 1Ω. 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
MΩ. 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.