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re: measuring the voltages:?? DON'T unless you like 1500 volts. That's
about 1000 volts at about 3-5 ma.? Definitely enough to be highly dangerous.

The backlights are CCFL lamps, evacuated tubes with some? mercury in
them.? They work like standard fluorescent lamps without a heater.

If the lamps show signs of darkening, they are likely suspect.

Unless you have a high voltage AC probe, (for a scope), don't do
anything with them.

There are some low voltage LED replacement kits on the market.

There are also replacement lamps available, specific to that display,
I'd think.

One thing to do is to take a scope probe and see if you can? pick up? a
magnetic field (use a small loop of insulated wire) by getting NEAR the
inverter transformer.? Another is to see how much low voltage current
you're pulling.? It might be a bit.

Inverters can also be had.

Another trick might be to get an ungrounded neon lamp (plastic rod! for
a handle) near the HV lines, or near the transformer.

Yet another would be to expose enough of the lamps (when installed in
the display), run the equipment in darkness, and see if you can see any
light from the tubes.? Keep your distance from the tubes, though and the
inverter.? There's a reason why the inverter has a nice coating of
insulating epoxy on it.

Be careful.

Harvey



On 4/16/2024 3:18 PM, Zack Widup wrote:
> Thanks. The backlight consists of two very small diameter glass tubes
> about 10 inches long and somewhere around 1/16 inch in diameter. There
> are two pink wires and one yellow wire coming out of that assembly and
> going to a plug on a board that appears to be a high-voltage power
> supply. The power supply board is even labeled "high voltage." I don't
> think that is an LED backlight. The pc board patterns going from a
> module on the power supply board are covered with epoxy up to the
> connector. I cannot figure out a way to measure the voltages out of
> the connector to the pink and yellow wires without cutting the wires.
>
> Zack
>
> On Tue, Apr 16, 2024 at 1:45?PM dan.meeks222@... via
> <> <dan.meeks222=[email protected]> wrote:
>
>? ? ?That probably uses LED backlighting, and that may have a separate
>? ? ?power connector. So look for that…
>
>? ? ?I doubt it’s got the old CCFL backlight, but that would certainly
>? ? ?be a separate connector as the voltage is too high to include with
>? ? ?signals.
>
>? ? ?Good luck and keep us posted.
>
>? ? ?dan
>
>? ? ?*From:*[email protected] <[email protected]> *On Behalf Of
>? ? ?*Zack Widup via <>
>? ? ?*Sent:* Tuesday, April 16, 2024 1:42 PM
>? ? ?*To:* [email protected]
>? ? ?*Subject:* [TekScopes2] DPO70804
>
>? ? ?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.
>
>? ? ?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.
>
>? ? ?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.
>
>? ? ?Can anybody give me any guidance or suggestions?
>
>? ? ?Zack
>
>