PB 741 reader crashes & shuts down on certain images

connoisseur · 12-29-2021, 08:48 PM

Hello all, I've been facing a strange bug on my Pocketbook PB 741 ever since I bought it a few weeks ago. I decided to make an account just now to ask for help cause I don't know what to do by myself anymore and I haven't seen this problem mentioned anywhere else.

Prelude
My device is a Pocketbook PB 741 with the latest firmware version U741.6.3.844 released on 20210514_191734. The bug in question happens when using the built-in reader app PB Reader with non-DRM files (I have not tested any DRM ones).

Problem

While reading various files in PDF and CBZ/CBR format, I've noticed that my device has the tendency to crash completely and shutdown when it attempts to display certain images, regardless of format. The crash is usually preceded by a freeze of the display. It normally happens like this:

1. I move to the next page
2. The screen fails to refresh completely, becoming blurry or parts of the previous page remaining visible more than they should
3. The screen freezes, although the device is technically responsive
4. I press the power button and the device goes to sleep without updating its screen
5. I press the power button again
6. During wake up, the device's screen bugs out by not refreshing completely, displays a weird vertical line somewhere on the screen and shuts down after leaving the screen in the bugged out state
7. I press the power button again and the device performs a cold boot and everything is back to normal... unless I try to open the problematic page again.

Here is an example image of how the display looks during step 6 - notice that the text is a bit harder to read than it should be, the page indicator at the bottom did not show the total number of pages before the device crashed, and there's a weird line in the middle of the screen that reminds of a dying GPU on a PC.
(https://imgur.com/a/8SdMNdp)

What I've tried

I have also done some experiments and discovered 2 points of interest.

1. When the screen initially freezes during step 3, I can avoid the crash by exiting the file I'm reading. When the screen freezes, if I press the home button, then the power button to put the device to sleep, then when I wake it up it starts in the home screen without issues. However, if I open up the same file again it will immediately crash and shut down.
2. This crashing bug is only limited to the built-in PB Reader I think. If I open the same files with koreader there are no problems whatsoever. However, koreader does not support color output for my device so it is not an option because I bought this model specifically for its color display.

And now I have come here to ask for help because I don't know what else to do. There are no newer firmware updates, a factory reset did not help, a reformat of the internal storage didn't either (though it did delete all the books that were pre-installed on the device and I didn't know that I should have backed them up in advance

), and koreader is not an option cause it doesn't support color for the PB 741 yet.

Example problematic images

I will attach a zip file to this post with a couple of images which almost always crash my device in this manner. I welcome anyone to try opening it with their device to see if they can go to the end and back without crashing. I cannot upload CBZs here so you will have to rename the extension from "zip" to "cbz" before copying it to your device.

What do these images have in common that causes this crash? The crash mostly happens on color pages, but I have witnessed it on some monochrome pages too. As far as I can tell, the only thing the images in my zip have in common is that they are fullscreen.

What should I do to resolve this problem?

connoisseur · 12-30-2021, 08:16 AM

I have also discovered that this crashing is more likely to happen the more the image is stretched to the edges of the screen. So for example, if a problematic page (like the ones I attached above) is zoomed to 100%, the crash will happen almost every time I try to open the page. However, if the zoom is 80% (or less) so that there is some empty space between the image and the edges of the screen, the crash is less likely to happen. Although, this obviously makes small text even harder to read...

connoisseur · 12-30-2021, 09:40 AM

I made another discovery just now while fiddling around with the constant crashes. Koreader didn't have any problems with these problematic images not because it's better than the built in PB Reader, but because it doesn't support color. It turns out that if I use PB Reader and set the color setting to -10 to make the entire screen monochrome, the problems disappear and I'm able to go through the images without crashing.

In other words, the crash happens specifically when trying to display certain images with color and in large size. I hope this helps narrow down the problem, but I don't know how to solve it or whether this is a software or hardware problem.

rkomar · 12-30-2021, 05:01 PM

I messed around with your file on my PB Colour (not Inkpad), and I did manage to get it to hang once while I was zooming in and out. The device did not crash, though.

I could also view it with the pbimageviewer app that I maintain. It shows colours, but not as nicely as the native app. If you are desperate, you could use it instead of the native app to view CBR/CBZ files.

connoisseur · 12-30-2021, 05:32 PM

You know, this is a really peculiar problem. Just now I was planning to force it to crash so I can take a better picture to show you what it looks like when it crashes badly and the screen ***** up seriously... yet it didn't crash once. Granted, it did hang up once or twice like your device did, but it never crashed. No matter how many times I turned the pages forward and back, it was stable. Yet, I didn't change anything on the device, except for the fact that I charged it back up to 100%. Before, when the crashes were especially egregious, my battery was around 28-35%. Since then I've charged it to 100% and now the crashes don't happen as far as I've experimented.

Perhaps this problem is related to the battery somehow?

12-30-2021, 08:16 AM	#2
connoisseur Junior Member Posts: 6 Karma: 10 Join Date: Dec 2021 Device: Pocketbook PB 741	I have also discovered that this crashing is more likely to happen the more the image is stretched to the edges of the screen. So for example, if a problematic page (like the ones I attached above) is zoomed to 100%, the crash will happen almost every time I try to open the page. However, if the zoom is 80% (or less) so that there is some empty space between the image and the edges of the screen, the crash is less likely to happen. Although, this obviously makes small text even harder to read...

12-30-2021, 09:40 AM	#3
connoisseur Junior Member Posts: 6 Karma: 10 Join Date: Dec 2021 Device: Pocketbook PB 741	I made another discovery just now while fiddling around with the constant crashes. Koreader didn't have any problems with these problematic images not because it's better than the built in PB Reader, but because it doesn't support color. It turns out that if I use PB Reader and set the color setting to -10 to make the entire screen monochrome, the problems disappear and I'm able to go through the images without crashing. In other words, the crash happens specifically when trying to display certain images with color and in large size. I hope this helps narrow down the problem, but I don't know how to solve it or whether this is a software or hardware problem.

12-30-2021, 05:01 PM	#4
rkomar Wizard Posts: 3,054 Karma: 18821071 Join Date: Oct 2010 Location: Sudbury, ON, Canada Device: PRS-505, PB 902, PRS-T1, PB 623, PB 840, PB 633	I messed around with your file on my PB Colour (not Inkpad), and I did manage to get it to hang once while I was zooming in and out. The device did not crash, though. I could also view it with the pbimageviewer app that I maintain. It shows colours, but not as nicely as the native app. If you are desperate, you could use it instead of the native app to view CBR/CBZ files.

12-30-2021, 05:32 PM	#5
connoisseur Junior Member Posts: 6 Karma: 10 Join Date: Dec 2021 Device: Pocketbook PB 741	You know, this is a really peculiar problem. Just now I was planning to force it to crash so I can take a better picture to show you what it looks like when it crashes badly and the screen *** up seriously... yet it didn't crash once. Granted, it did hang up once or twice like your device did, but it never crashed. No matter how many times I turned the pages forward and back, it was stable. Yet, I didn't change anything on the device, except for the fact that I charged it** back up to 100%. Before, when the crashes were especially egregious, my battery was around 28-35%. Since then I've charged it to 100% and now the crashes don't happen as far as I've experimented. Perhaps this problem is related to the battery somehow?

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