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Troubleshooting Procedures
WFM90D and WFM91D Service Manual
6-41
6. Check for a voltage reading of +2 VDC on the voltmeter with theWFM90D
or WFM91D turned on, and a reading of +8 to +9 VDC with the instrument
turned off. The voltage will slowly rise when the instrument is turned off.
7. If the voltage reading in the previous step was correct, replace the batteries.
If the voltage reading was incorrect, replace the Bottom board.
WARNING. To prevent electric shock and high-voltage arcing, do not operate the
Backlight power supply with the LCD module removed. High voltages in excess
of 1 kV can be present on the Backlight power supply leads when operated open
circuit.
If the LCD module is removed, always remove the Backlight board before
powering up the instrument for test.