Can you replace a burnt out CCFL bulb inside an old laptop LCD screen with an LED bulb? Theoretically, yes, but the practical technical considerations to achieve this make it a great challenge.
Let’s consider one case example. I’ve bought a new LCD screen and inverter for a Dell Inspiron e1505 laptop because the CCFL bulb inside the old screen failed from the previous owner disliking display mode power save timeout after running a screen saver for so long. They wanted the screen to stay powered on and show the screen saver running all the time. As a consequence, the CCFL bulb failed well before its expected failure date based off of the intensity of use of the machine. But anyways, if I eventually replace the CCFL bulb inside with a new one, I’ll have a spare LCD screen at my disposal.
So, let’s get the rundown of the actual parts inside the LCD display. First of all, the part number of the inverter is LJ97-00680A. This is a part that is apparently manufactured by Dell. But, more interesting are the parts on the board itself. There are really only two integrated circuit packages on the board, the big rectangular one is a housing for the high-voltage inverter. The small square one, that is clearly an integrated circuit package of some sort. Reading the label that is visible from my up-close photos, it is pretty similar to the Maxim MAX8759ETI+, and I was able to find this datasheet online! The part itself, however, is obsolete and no longer in production.
My read of the IC package label:
MAXIM
8759E
TI605
+ NTAK
20201012/DuckDuckGo maxim 8759E TI605 NTAK
20201012/DuckDuckGo maxim 8759ETI605 NTAK
20201012/DuckDuckGo maxim MAX8759E TI605 NTAK
20201012/DuckDuckGo maxim MAX8759ETI605 NTAK
20201012/DuckDuckGo maxim MAX8759ETI 605 NTAK
20201012/DuckDuckGo DuckDuckGo maxim MAX8759ETI
20201012/https://datasheets.maximintegrated.com/en/ds/MAX8759.pdf
20201012/https://www.digikey.com/en/products/filter/pmic-lighting-ballast-controllers/751?s=N4IgTCBcDaILIEEAaAOA7AVgJwgLoF8g
20201012/https://www.digikey.com/en/products/detail/maxim-integrated/MAX8759ETI/11548192
20201012/https://4donline.ihs.com/images/VipMasterIC/IC/MAXM/MAXMS19462/MAXMS19462-1.pdf?hkey=EC6BD57738AE6E33B588C5F9AD3CEFA7
This is an LCD inverter controller integrated circuit, complete with SMBus (I2C) support for dimming control and other advanced features. Dimming can also be controlled via PWM and an ambient light sensor, though the original laptop never used the ambient light sensor support! One thing I do like about the chip’s advanced features are the safety features, the ability to detect bulb failure and other similar events, enter a shutdown mode, and set an error condition register that can be read from SMBus. Now, if only I knew if my Dell laptop had hardware support for reading that state info, then it’s just be a matter of getting that software support into Linux.
Second, the part number of the screen is Samsung LTN154X3-L06. I found it easy to find the datasheet for LTN154X3-L01, but it was considerably more challenging to find the datasheet for LTN154X3-L06. When I did find it, it was marked with “Samsung secret,” apparently originally delivered to Toshiba. As is typical with these confidential documents, it was wrought with a number of minor editorial errors: spelling and grammar issues were caught, minor technical issues are reasonable to assume. However, this datasheet is overall more detailed. Apparently only laptop manufacturers were permitted to receive the more detailed information.
20201012/DuckDuckGo LTN154X3-L06
20201012/DuckDuckGo LTN154X3-L01 datasheet
20201012/https://pdf1.alldatasheet.com/datasheet-pdf/view/1132231/SAMSUNG/LTN154X3-L01.html
20201012/DuckDuckGo LTN154X3-L06 datasheet
20201012/https://datasheet4u.com/datasheet-pdf/Samsung/LTN154X3-L06/pdf.php?id=672537
20201012/https://datasheet4u.com/datasheet-parts/LTN154X3-L06-datasheet.php?id=672537
One thing I had to remind myself in regard to the wiring of the inverter and the LCD screen. The Dell laptop uses a special cable to attach the separate connectors of both to a single cable, which then connects to the laptop’s motherboard. The LCD screen itself only has one cable for data input, and one cable for the CCFL bulb input, there is no special cable for output from the monitor to data input for the inverter like I once wrongly thought may be the case.
Good news, I’ve found one of those clunkly VGA interface boards specifically designed for this LCD screen.
20201012/http://www.lcdcontrollerdiy.com/2018/12/05/vga-lcd-controller-board-work-for-ltn154x3-l06-ltn154x3-l07-lcd-panel/
20201012/https://www.ebay.com/itm/VGA-LCD-Controller-Board-Work-for-LTN154X3-L06-LTN154X3-L07-LCD-Panel/182350335880?hash=item2a74ed4f88:g:UnsAAOSwIgNXkxrY
Yeah, that was the old way I’ve documented on how to use an old laptop LCD screen with new applications, Raspberry Pi in particular. But, the bigger question. I know what it takes to control the inverter board. Can you interface LVDS directly with Raspberry Pi to attach the entire display more directly? Indeed you can! LVDS4PI is the name of the game, a project that puts an LVDS driver chip onto a Raspberry Pi HAT, and its successor, LVDS4PI EVO. I’m not sure how speedy it can perform on a Raspberry Pi Zero, I’d guess it unfortunately wouldn’t be as good as the original laptop due to the BCM2835 not supporting LVDS directly in its GPU pipeline.
But, the hints I’m picking up, maybe you can send DSI or DPI to an LVDS controller and then that would be quite speedy. However, some options may require a Raspberry Pi Compute Module rather than a Raspberry Pi Zero, and that’s where the bummer is.
20201012/DuckDuckGo raspberry pi lvds
20201012/https://www.youtube.com/watch?v=JmE5L34jfi8
20201012/https://www.raspberrypi.org/forums/viewtopic.php?p=1527642
20201012/https://www.youtube.com/watch?app=desktop&v=aJ_nn7YlihE