Power Supply - Keysight Technologies 34959A Service Manual

Unit fails self-test
1 Check the display for the power on self test results.
2 Remove all plug-in modules from the mainframe and any connections to the
3 If the self test still fails, remove the internal DMM from the instrument. The
4 Self-test errors are described beginning on

Power Supply

The main power supply provides +12 Volts. All other power supplies are derived
from this supply. To test the main power supply:
Exposed Mains. When the instrument cover is removed to test the power
WARNING
supply, the ac mains are exposed. Any voltages greater than 30 Vrms,
42.4Vpeak and 60 Vdc are considered hazardous (IEC 61010-1). Use extreme
caution. Failure to recognize and observe normal safety precautions could
result in personal injury or death.
1 Disassemble the instrument as described beginning on
2 Use a DVM to check that the power supply output is +12 V ± 0.6 V.
3 Use an oscilloscope to verify there is no ac oscillation on the +12 V power supply.
Replace the power supply assembly if +12 V is not present.
Keysight 34980A Service Guide
Analog Bus. Run the self-test again. A passing self-test indicates a problem
with a plug-in module. Replace the plug-in modules one at a time to isolate
the failing module.
instrument should turn on and pass self-test without the internal DMM
installed. Disassembly procedures begin on
Test the power supply output at the red leads on the power supply connector
to the communications board.
a The +12 Volt supply is always on when the ac power is applied to the
instrument. Test for loading errors by unplugging the power supply
connector from the communications board.
Troubleshooting and Diagnostics
page 121.
page 79.
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