AU Optronics B101EAN01.5 Backlight Power

I’ve pulled the LED backlight illumination panel out of an AU Optronics B101EAN01.5 LCD panel, which was in turn salvaged from an Acer Aspire Switch 10 (SW5-012) tablet/laptop convertible. I want to see if I can get it to light up. Using my multimeter I found test points corresponding to all six control lines on the backlight, and soldered wires to all of them. The next task is to determine what these wires are.

The other end of those wires were crimped and assembled into a six-pin connector with 0.1″ spacing. I first arranged them in whatever happened to be convenient, but then I changed my mind and rearranged them to be in the same order as that on the backlight cable. From top to bottom: Power, ground, FB1, FB2, FB3, and FB4.

This gave me something suitable for breadboard exploration. I have two hypothesis about what the FB connectors are. Since power and ground were already identified, I thought maybe these are control lines (gates) for MOSFETs in line with each string, which implies I could turn on a LED string by pulling its signal high. But if I look at precedence set by the LG LP133WF2(SP)(A1) panel I took apart earlier, these could be four current sinks for four LED strings.

To test both concepts simultaneously, my breadboard exploration wired one string to a pull-up resistor in case FB is a MOSFET gate, and another string to a pull-down resistor in case it is LED current sink.

I started seeing a dim glow when I turned the power supply up to 17V. To determine which hypothesis was correct, I removed the pull-down resistor and it went dark. So FB1 through FB4 are current sinks for four strings. As a double-check, I calculated voltage drop across the pull-down resistor and calculated the current flow to be 1.4mA. This is far too high for a MOSFET gate but completely consistent with current-limiting resistor for a dimly lit LED.

Hooking up a current-limiting resistor to each of FB1 through FB4, the backlight has dim but usable illumination starting at about a 15.6V drop across an individual LED string. Whenever I find a project for this light, I will need to either solder more permanent current-limiting resistors, or find an intelligent LED controller with a more efficient current-limiting control scheme.

There is one remaining mystery: If the VOUT wire is voltage source, and FB1 through FB4 are current sinks, why is there a line connected to the ground plane on the control circuit board? It feels like there’s another aspect of this backlight I have yet to discover. Or possibly destroyed by clumsy overvoltage on my part. Either way, it doesn’t seem to be critical for illuminating this backlight, so I’ll leave that mystery for another day.

AU Optronics B101EAN01.5 Backlight Wiring

I have a broken Acer Aspire Switch 10 (SW5-012) that I have taken apart. Among the pieces I salvaged was the screen, an AU Optronics B101EAN01.5 whose 1280×800 resolution is not terribly interesting in this era when even cell phones have higher resolution displays. So I decided the most interesting thing to do is to liberate its LED backlight for potential future projects.

The backlight connector has six visible conductors. Two conductors are wider than the rest, which imply power and ground to me. There is a test point labeled VOUT adjacent to this connector, and my meter confirms it corresponds to the topmost wide conductor. The meter also confirmed the second wide conductor has continuity to the ground plane of this circuit board, so power and ground confirmed.

What does that mean for the four remaining thin conductors? Looking around the backlight control IC, I looked for a likely group of four test points and found FB1, FB2, FB3 and FB4. Meter confirms they correspond to the remaining four conductors on the backlight cable. “FB” probably doesn’t mean Facebook in this context, but I’m not sure what it would represent. I’m just glad they were numbered.

As for the backlight control IC itself, the large AUO letters say it is something AU Optronics produced for internal consumption. The earlier LG panel project found a TI TPS61187 chip with publicly available documentation, but here I found no documentation for an AUO L10716 controller. Since the chip is so tiny it’s pretty probable I’ve misread the numbers, but no search hits on the variations I could think of either: LI0718, L10216, etc. If I had found a test point labeled PWM I would be tempted to see if I can get it running with an Arduino PWM signal, but I saw test points labeled SCL and SDA telling me this is an I2C peripheral and my skill level today isn’t good enough to reverse engineer it without official documentation of its I2C protocol.

So instead of trying to interface with the existing backlight control chip as I did on the LG backlight, here I will interface with the backlight LEDs directly. I found test points corresponding to all six wires on the backlight connector and soldered wires to all of them. Then I used hot glue to help hold them down and relieve strain, as I don’t want to lift a pad again!

With the wires securely attached, I need to figure out what they actually do.

Acer Aspire Switch 10 (SW5-012) Backlight Removal

While I took apart the base unit of this dead Acer Aspire Switch 10 (SW5-012) tablet/laptop convertible, the main display had been left under the punishing direct heat of southern California summer sun. I don’t like fighting glue, but heat at least helps reduce their tenacious grip. I pulled out my prying tools from iFixit and plunged into the seam between gray and black plastic surrounds holding its AU Optronics B101EAN01.5 screen in place.

The double-sided adhesive foam tape was thickest around the left and right sides, gripping tightly enough that I broke the frame on both sides trying to peel them off. There were slightly less of it across the top, and surprisingly little across the bottom.

I had hoped the LCD module would pop free once the touchscreen digitizer glass had been freed from its frame, similar to how an Amazon Fire tablet was put together. But no such luck, there appears to be more adhesive involved.

Once I pushed a pick into the gap between the digitizer glass and the LCD polarizer, I realized the bad news: they have been glued together across the entire visible front surface of the screen. It’s going to take a lot of effort to separate them and I don’t see how it could possibly be worth the effort.

My objective here is the LED backlight, so just as I did for the Chromebook cracked screen and the Amazon Fire screen, I peeled back the black tape holding the LED backlight to the LCD. Starting with the bottom section to expose the integrated driver board.

I am starting to recognize the signs of a LED backlight power connection: a few connectors separate from the high-density connectors used for controlling LCD pixel data. An inductor and a diode for voltage boost conversion, and an IC controlling it all.

The black tape holding this display module together is much more difficult to remove than those encountered on previous screen backlight salvage projects. The glossy substrate is weaker than the adhesive, causing it to easily stretch and break. Now that I’ve identified the portion I cared about for my project, I pulled out a blade and cut the rest of the tape allowing me to open up this display module.

Once the backlight folded away from the LCD pixel array, I can see I’ve already cracked at least one LCD glass layer in my effort to pry it from the front digitizer glass. I’m not even going to try to salvage the polarizer filter from this one, so my blade continued its work cutting all pixel data lines to free the backlight for further examination.