Troubleshooting Kindle 4: Motherboard works, screen is blank

[Darthagnon]

Following my previous issues with my Kindle 4, my mum happened to pass me a non-functional Kindle 4 for spare parts. My original is a ship of Theseus, but working fine, so I've now got a spare to play with.

It charges, powers on, and I even dumped the books that were on it (a bunch of sci-fi omnibuses, much better than the usual teen romance rubbish I've found on old Kindles). However, the screen is blank and displays nothing. It appears to be undamaged, no marks anywhere.

I've opened it up, but no clues there. Does anyone here know where I should look on the circuit board for troubleshooting this? I'm guessing the motherboard is generally fine, as it still boots, charges, connects to USB and read/writes. Replacing the screen is likely not worth it, but as it is quite nice and unscratched, I'd like to save it from ewaste if I can.

[axu2]

Amazon takes broken Kindles for trade-in for 20% off on a new Kindle.

[Darthagnon]

While playing with a broken donor Kindle 4 I got, I thought, "Why don't I connect the battery to this blank Kindle 4?" So, I took the back off both, and because the batteries were still glued in, I made the beast with ~~two backs~~ two fronts by connecting up the (good) donor battery to the blank Kindle 4. It booted. So I connected back its original battery and it's been working fine to this day A story with a happy ending, unlike Othello.

[jackm8]

Glad you made it working. So the problem was a faulty battery on that one?

[Darthagnon]

Yes, the battery was the issue. I get the impression maybe the battery controllers in the Kindle 4s are not very good - they're supposed to stop the Li-ion from overcharging and from dropping below a certain level, but after seeing yet another Kindle 4 with the same issue, I'm thinking that if left to discharge, they can actually get too low and flip some sort of flag and the screen remains blank. I'm going to try jump-starting this new one, too, see if that fixes it.

EDIT: seems to have reoccurred with the original Kindle. Basically, the battery charge level drops too low, the screen goes to the "plug in to power" image, then when you do, it goes blank and stays blank until the Kindle is jump-started with a higher voltage from a good battery or power supply. I need to see if those metal pads on the back (originally for the Amazon light case) can be used for jump-starting, as disassembly every time I leave them in a drawer for too long is not sustainable.

[Darthagnon]

I found a better solution on this thread: to hard reset older Kindles, you need to hold the button for 30s (the charging/power light will go out, keep holding), then release, then hold for 10s. Basically, it takes 2 or 3 long presses to reset, not 1x long press as suggested in many places. The screen will flash black, then the little boy under a tree will appear and it will reboot. Much faster than disassembling and jump-starting the battery.

This worked to get both blank-screened Kindle 4s back up and running.

[Frogm4n]

Have you tried re-plugging it in? As in, plug it in and wait for the charge controller to show the orange light, the un- and re- plug it in withing a second or two. That often works for me to get the charge controller to wake up with the first plug in, then it will run for a short time on capacitors, and then on the second plug in it will see the charger and start taking voltage. It might still need 10-30 minutes sitting plugged in to boot on it's own. I usually do this with a USB power meter inline so I can see how much amperage it is taking to know when the controller is on and when it has started pulling enought power to be charging the battery and booting the board.