If you haven't seen it this is a service manual with schematics for a Lecroy Waverunner LTxxx scope: http://www.ko4bb.com/manuals/49.195.59.33/LeCroy_LTXXX_WaveRunner1_Digital_Storage_Oscilloscope_Service_Manual.pdf
page 8-55 shows a 5 pin connector that goes to the backlight they are as follows:
1. +12V
2. GND
3. Open collector enable signal
4. GND
5. Connected to a HC4051 and looks like it might control brightness.
The LED strips arrived (I bought four) including the converters. Using a bench power supply, I tinkered with the LEDs to figure out what needed to be adapted into the LeCroy scope to incorporate them.
On a side note, knowing the converter board needs to be adapted to the exiting connector in the scope, I cut the wires to perform some bench testing. I didn't realize I flipped the connector ends (the end that was connected to the board was now the open end that I cut) and resulted in the red wire being connected to ground and the black to Vcc. It took several minutes (and two boards) before I discovered the input voltage was reversed due to plugging the opposite end.
I'm extremely confused over this scope. As listed above, the pins on the existing board are correct and pin 3 needs to be pulled low for the screen to turn on (I assume this is something to do with screen saver or whatever - but I verified that open and the screen is off, pulled low and screen is on).
Pin 5 has a few milli volts on it regardless if it's open or connected, the voltage doesn't change with adjusting the screen brightness (although the screen brightness works because I can dim the screen to off all the way to 100% brightness), Using a current meter, I tried measuring current and didn't see any fluctuation (although maybe I should have used a Fluke in series), etc...
After trying to measure voltage, current, and changes in both while adjusting brightness, I removed the CCFL so I could look at the lamp while adjusting the brightness, took the LED strip and let it shine down the screen (although it wasn't perfect because I rested it on top, the image was more than visible enough to see the screen), and adjusted the brightness. The CCFL didn't change brightness at all.
My confusion: I thought screen brightness was caused by the CCFL changing intensity and this doesn't seem to be the case. My other confusion is what the heck is pin 5 doing? The screen remains off if pin 5 is blank, but I don't understand the need for this circuit.
If I had to guess, I'd assume a brightness pot exists somewhere, or a menu setting exists somewhere that I'm not locating, however, I haven't see anything that points me to a pot or a menu setting.
The replacement LED strip needs some work to fit into the scope; nothing too difficult. It needs +12v (12v to 30v) which the scope provides, ground, 0-5v for brightness, and >2.7v to 5v for enable.
From current measurements I took, the 12v needs almost 1A (scope should provide that) but brightness and enable take very little current which makes things much easier.