I have a DPO70804 scope. The display is dark. I have determined that the fluorescent backlight tubes are not lit. I connected an XGA monitor to the XGA socket on the rear, and the XGA monitor displays the scope display and all functions are working correctly.
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I have been trying to determine if the display tubes or the voltage supply for those tubes is bad, or if the problem is elsewhere. The service manual I have for the unit contains no schematics nor any info on a way to test the fluorescent display circuit.
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The power supply board has a 20-pin plug with voltages on the pins. All the voltages are correct as per a drawing in the manual, except for the -5 volt pin (pin 18). That measures 0 volts. But on the drawing, there is an asterisk next to the -5 volt pin, with no explanation I can find anywhere of what the asterisk means. The PS-ON pin measures 0 volts and the PW-OK pin measures +5 volts.
