After a several-month hiatus, I finally got the rest of the hardware I needed to finish refitting an old 17″ LCD monitor with LED backlights.
So, without further ado, I give you the LED driver board. It’s a simple mc34063 buck converter, with an extra input from the logic board to control the brightness. It has a mounting hole (more on that folly later) to mount it on one of the existing standoffs.
Many of the components that I used were pulled off the existing driver board: the inductor, freewheel diode, and capacitor. You can look at the schematic and board layout if you like.
Next step, modify the existing driver board so that it cuts off power to the backlights exactly the same way it did before. With a regular CCFL inverter, the logic board controls a PNP (or was it P-channel?) transistor to cut off power to the inverter controller. I hijacked the same circuitry, replacing the existing transistor with a higher-current FU9024N, which not only matched the pinout, but was also scavenged from the original driver.
Now, on to testing. This is why I included a pot–so I could get the perfect 12V maximum current to the LEDs. (it’s hard to see the DMM display, I know)
To get the driver board in the case, I cut out a rectangular section of the old driver board. For perspective, all that bare PCB used to be dedicated to the CCFL backlight inverter. Methinks mine is slightly smaller.
And yes, that’s a bunch of fiberglass dust all over the other parts. At least it’s not conductive, because I’m too lazy to clean it up.
From here, it’s a matter of assembling the whole package.
There were a few speed bumps on this final stretch. I cut the wires for the backlights a bit snug, so it was a bit acrobatic to get it all together. The first time I got it all together, I turned it on to realize that half of my bottom light wasn’t working. With all the abuse it had gone through, one of the pads had lifted. So I had to tear down the whole monitor. And that mounting hole? Well, it didn’t exactly hold the board flat. A little electrical tape solved that problem.
But in the end, here it is. Working at last.
I don’t suppose you would have any technical document showing the components for the inverter side so I could do something similar? or, perhaps if you would be willing to send me more info and high resolution pics. I have the same exact monitor (a few of them) and I’ve been considering doing this but I could use some advice Thanks
The schematic and board layout are linked in the post above. When designing the circuit, I followed the calculations in the datasheet for the CM34063–it’s fantastically detailed, with equations for calculating all the values for all the various components. If you’re looking for the exact values I used, well, I don’t know if I still have those notes around. I’ll look when I get to work tomorrow, but I can’t promise results. IIRC, the inductor I recycled from the original inverter and the cap is a 1000uF cap.
Actually what I was looking for was info on what can/needs to be removed from the original power supply inverter circuit to completely disable while maintaining the ability to let the monitor turn off the LED backlighting. I see in the pictures that you removed most if not all the backlight inverter circuit components and I was going to do the same but not sure where to start and stop… I have a good idea but was looking for more information if available. If I can figure this out I planned to buy several of the LED PCB’s from your shop and retrofit some identical monitors I have laying around.