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koraks · 02-27-2025, 04:36 AM

Hi community,
New user here; sorry if I missed anything essential in posting this thread. Likewise, if my problem has already been discussed, kindly link me to the threads/sites in question so I can do some reading.

The device is a PocketBook Touch Lux 4 which has been in daily use for the last 5 years or so. The problem description is that the device won't turn on, which is to say:
* The device does respond to the power button: power button light comes on, backlight comes on, Vcc comes on to ca. 3.2V (measured at test points on PCB). Once turned on, the device can also be powered down by keeping the power button pressed for 15 seconds or so, after which Vcc drops to zero.
* The display is unresponsive. It shows the "Touch Lux 4" screen with the marketing specs below. Display does not change, does not show any artefacts etc.
* When plugged into USB on a computer, I don't get device enumeration in Windows and no extra drive pops up in explorer etc.
* Battery voltage looks normal (ca. 4.2V). Device appears to charge just fine. Vcc looks normal (ca. 3.2V) as described above.
* On the test points for the display, I get some of the voltages I'd expect for an eInk display.

I've tried starting the device with just the battery and the display connected to the main PCB, so no backlight and touchpad controller. The behavior is the same.

I have not (yet) hooked up a computer to the UART test pads to see what happens. I do notice that the voltage on TX drops briefly in the seconds direct after power-up, which suggests the device is outputting something to UART.

Is this a known failure mode of this device? If so, what are the probable causes?

I am reasonably well-equipped with a scope, SMD soldering equipment and decent hobby-level working knowledge of embedded systems. The main factor is how much time I want to spend on this, but I hate throwing stuff away even if it seems 'broken' (my wife, whose device this is, has of course already ordered a new one, so there's no pressure...)

Thanks for sharing any thoughts you may have!

02-27-2025, 04:36 AM	#1
koraks Junior Member Posts: 7 Karma: 10 Join Date: Feb 2025 Device: PocketBook Touch Lux 4	PB TL4 does not turn on (sort of) Hi community, New user here; sorry if I missed anything essential in posting this thread. Likewise, if my problem has already been discussed, kindly link me to the threads/sites in question so I can do some reading. The device is a PocketBook Touch Lux 4 which has been in daily use for the last 5 years or so. The problem description is that the device won't turn on, which is to say: * The device does respond to the power button: power button light comes on, backlight comes on, Vcc comes on to ca. 3.2V (measured at test points on PCB). Once turned on, the device can also be powered down by keeping the power button pressed for 15 seconds or so, after which Vcc drops to zero. * The display is unresponsive. It shows the "Touch Lux 4" screen with the marketing specs below. Display does not change, does not show any artefacts etc. * When plugged into USB on a computer, I don't get device enumeration in Windows and no extra drive pops up in explorer etc. * Battery voltage looks normal (ca. 4.2V). Device appears to charge just fine. Vcc looks normal (ca. 3.2V) as described above. * On the test points for the display, I get some of the voltages I'd expect for an eInk display. I've tried starting the device with just the battery and the display connected to the main PCB, so no backlight and touchpad controller. The behavior is the same. I have not (yet) hooked up a computer to the UART test pads to see what happens. I do notice that the voltage on TX drops briefly in the seconds direct after power-up, which suggests the device is outputting something to UART. Is this a known failure mode of this device? If so, what are the probable causes? I am reasonably well-equipped with a scope, SMD soldering equipment and decent hobby-level working knowledge of embedded systems. The main factor is how much time I want to spend on this, but I hate throwing stuff away even if it seems 'broken' (my wife, whose device this is, has of course already ordered a new one, so there's no pressure...) Thanks for sharing any thoughts you may have!