There's a fair amount of difference in CCFL voltages depending on the size of the tubes.
If the OP doesn't want to play with high voltages (and those are nasty!), then I'd look for a replacement LED strip made for that display.? It would come with a control board.
The current through the CCFL lamps is limited by the driver and board circuitry, so the board is matched to the lamps.
Harvey
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On 4/16/2024 3:26 PM, dan.meeks222@... wrote:
Okay yes so that¡¯s a CCFL (cold cathode fluorescent) backlight.
You will most likely find the backlight driver on a separate board (because of high voltage AND noise).
CCFL initially goes up to a high ¡°strike¡± voltage, then after the tube conducts the voltage drops. And it¡¯s AC voltage, keep that in mind if you try to measure it.
The CCFL driver may shut down if it detects that the tubes do not fire. But most likely that driver has fried.
I guess make sure the driver has DC input power, and maybe look for AC voltage on the output when you apply power. It¡¯s not 60Hz, so keep that in mind. Your DMM may or may not give you an accurate reading.
You can buy generic CCFL drivers but of course OEM is best if you can get it. Maybe Tek still sells it?
If you need to use a generic driver, try to find someone on the group that knows what voltage you need. I don¡¯t know if there is much difference in CCFL voltages.
Dan
*From:*[email protected] <[email protected]> *On Behalf Of *Zack Widup via groups.io
*Sent:* Tuesday, April 16, 2024 2:19 PM
*To:* [email protected]
*Subject:* Re: [TekScopes2] DPO70804
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 groups.io <> <dan.meeks222@...> 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 groups.io <>
*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
