Tablet battery replacement and alloc_device_open fail?

I had to do a battery replacement on an Android 4.x tablet Denver TAC-97032. The battery had been obtained from the manufacturer as aftermarket part; it is however not of the same size as the original one. Still, I opened the tabled, desoldered the old battery, and soldered the new one; behavior thereafter is: * If I just plug in the charger, I get the Android "battery fills" animation for a while, the animation shows charging, and then it disappears, as usual. Good - means battery is detected and is mounted properly. * If I boot with Power + Vol Up, I get into the recovery, which here just shows the "dead android" picture; there are no extra menus for ADB sideload or similar, so basically it just sits there; adb can also see a "recovery" device, and adb reboot is also recognized and works * If I boot with just Power: first the DENVER splash is shows, then an Android splash screen is shown, then screen goes black (but there is still backlight it seems); device appears dead, but if I hold Power to force shutdown, at end a click from the speaker is heard and flash from screen seen - meaning the device ran also under the black screen. At the black screen, I tried adb - and luckily, it worked:

$ ./adb.exe logcat
--------- beginning of /dev/log/main
I//system/bin/e2fsck(   67): e2fsck 1.41.11 (14-Mar-2010)
I//system/bin/e2fsck(   67): /dev/block/nande: clean, 5183/76800 files, 205676/307200 blocks
I/logwrapper(   67): /system/bin/e2fsck terminated by exit(0)
I//system/bin/e2fsck(   72): e2fsck 1.41.11 (14-Mar-2010)
I//system/bin/e2fsck(   72): /dev/block/nandh: clean, 15/20496 files, 2623/81920 blocks
I/logwrapper(   72): /system/bin/e2fsck terminated by exit(0)
--------- beginning of /dev/log/system
I/USB3G   (   85): usb 3g monitor v0.1 start
I/USB3G   (   85): event { 'add', '/devices/platform/sw_hcd_host0/usb1', 'usb', '', 189, 0 }
I/USB3G   (   85): event { 'add', '/devices/platform/sw-ehci.1/usb2', 'usb', '', 189, 128 }
I/USB3G   (   85): event { 'add', '/devices/platform/sw-ohci.1/usb3', 'usb', '', 189, 256 }
I/Netd    (   80): Netd 1.0 starting
I/Vold    (   79): Vold 2.1 (the revenge) firing up
D/Vold    (   79): Volume sdcard state changing -1 (Initializing) -> 0 (No-Media)
D/Vold    (   79): Volume extsd state changing -1 (Initializing) -> 0 (No-Media)
D/Vold    (   79): Volume usbhost1 state changing -1 (Initializing) -> 0 (No-Media)
D/Vold    (   79): Volume sdcard state changing 0 (No-Media) -> 1 (Idle-Unmounted)
I/SurfaceFlinger(   81): SurfaceFlinger is starting
I/SurfaceFlinger(   81): SurfaceFlinger's main thread ready to run. Initializing graphics H/W...
E/[Gralloc-ERROR](   81): int alloc_device_open(const hw_module_t*, const char*, hw_device_t**):436 UMP open failed with 1
E/FramebufferNativeWindow(   81): couldn't open framebuffer HAL (Operation not permitted)
E/[Gralloc-ERROR](   81): int alloc_device_open(const hw_module_t*, const char*, hw_device_t**):436 UMP open failed with 1
E/FramebufferNativeWindow(   81): couldn't open gralloc HAL (Operation not permitted)
E/SurfaceFlinger(   81): Display subsystem failed to initialize. check logs. exiting...
I/        (   82): ServiceManager: 0xf958
I/AudioFlinger(   82): Loaded primary audio interface from sunxi audio HW HAL (audio)
I/AudioFlinger(   82): Using 'sunxi audio HW HAL' (audio.primary) as the primary audio interface
I/CameraService(   82): CameraService started (pid=82)
I/AudioFlinger(   82): AudioFlinger's thread 0x1c7b0 ready to run
W/AudioFlinger(   82): Thread AudioOut_1 cannot connect to the power manager service
I/AudioPolicyService(   82): Loaded audio policy from LEGACY Audio Policy HAL (audio_policy)
I/SurfaceFlinger(  129): SurfaceFlinger is starting
I/SurfaceFlinger(  129): SurfaceFlinger's main thread ready to run. Initializing graphics H/W...
I/[Gralloc](  129): using (fd=10)
I/[Gralloc](  129): id           =
I/[Gralloc](  129): xres         = 1024 px
I/[Gralloc](  129): yres         = 768 px
I/[Gralloc](  129): xres_virtual = 1024 px
I/[Gralloc](  129): yres_virtual = 1536 px
I/[Gralloc](  129): bpp          = 32
I/[Gralloc](  129): r            = 16:8
I/[Gralloc](  129): g            =  8:8
I/[Gralloc](  129): b            =  0:8
I/[Gralloc](  129): width        = 163 mm (159.568100 dpi)
I/[Gralloc](  129): height       = 122 mm (159.895081 dpi)
I/[Gralloc](  129): refresh rate = 60.12 Hz
D/libEGL  (  129): loaded /system/lib/egl/libEGL_mali.so
D/libEGL  (  129): loaded /system/lib/egl/libGLESv1_CM_mali.so
D/libEGL  (  129): loaded /system/lib/egl/libGLESv2_mali.so
E/SurfaceFlinger(  129): couldn't find an EGLConfig matching the screen format
W/SurfaceFlinger(  129): ro.sf.lcd_density not defined, using 160 dpi by default.
I/SurfaceFlinger(  129): EGL informations:
I/SurfaceFlinger(  129): # of configs : 21
I/SurfaceFlinger(  129): vendor    : Android
I/SurfaceFlinger(  129): version   : 1.4 Android META-EGL
I/SurfaceFlinger(  129): extensions: EGL_KHR_image EGL_KHR_image_base EGL_KHR_image_pixmap EGL_KHR_gl_texture_2D_image EGL_KHR_gl_texture_cubemap_image EGL_KHR_gl_renderbuffer_image EGL_KHR_fence_sync EGL_ANDROID_image_native_buffer
I/SurfaceFlinger(  129): Client API: OpenGL ES
I/SurfaceFlinger(  129): EGLSurface: 5-6-5-0, config=0x0
I/SurfaceFlinger(  129): OpenGL informations:
I/SurfaceFlinger(  129): vendor    : ARM
I/SurfaceFlinger(  129): renderer  : Mali-400 MP
I/SurfaceFlinger(  129): version   : OpenGL ES-CM 1.1
I/SurfaceFlinger(  129): extensions: GL_OES_byte_coordinates GL_OES_fixed_point GL_OES_single_precision GL_OES_matrix_get GL_OES_read_format GL_OES_compressed_paletted_texture GL_OES_point_size_array GL_OES_point_sprite GL_OES_texture_npot GL_OES_query_matrix GL_OES_matrix_palette GL_OES_extended_matrix_palette GL_OES_compressed_ETC1_RGB8_texture GL_OES_EGL_image GL_OES_draw_texture GL_OES_depth_texture GL_OES_packed_depth_stencil GL_EXT_texture_format_BGRA8888 GL_OES_framebuffer_object GL_OES_stencil8 GL_OES_depth24 GL_ARM_rgba8 GL_OES_EGL_image_external GL_OES_EGL_sync GL_OES_rgb8_rgba8 GL_EXT_multisampled_render_to_texture GL_OES_texture_cube_map GL_EXT_discard_framebuffer GL_EXT_robustness
I/SurfaceFlinger(  129): GL_MAX_TEXTURE_SIZE = 4096
I/SurfaceFlinger(  129): GL_MAX_VIEWPORT_DIMS = 4096 x 4096
I/SurfaceFlinger(  129): flags = 00000000
D/display (  129): ####disp_init, mode:0,out_type:1,tv_mode:0,app_width:1024,app_height:768
D/DisplayDispatcher(  129): display dispatcher enabled

... and here logcat stops - there are no further messages. So, the primary error seems to be "Display subsystem failed to initialize", and it explains the black screen; however I cannot really tell: * Is this a hardware cause: maybe during battery replacement, I accidentally disconnected some pin from the display, so even if I get splash screens shown at start, there is an error later when normal operation is initialized? * There are very few resources online mentioning this error, and I think I got to an IRC chat log, where a factory reset was recommended for an error like this. I would imagine, that maybe there is an ID on the battery of sorts, and since now it is changed from the original one, the OS sees that as an error, and refuses to proceed. Obviously, I do NOT want to do a factory reset - because then, I lose all of the data on the device (I'd do an adb backup, but that typically raises a prompt on the device, and since the screen does not work, I couldn't have allowed it even if the system booted to a state where it would have shown the prompt) So, my questions are: * Would anyone know what is more likely as the cause of ump_open error: hardware wire misconnection, or maybe differing ID of the battery? * Is it realistic to hope that factory reset would solve this problem? * If I need to do factory reset, is there any way I can back up this device purely from adb (but not using any GUI elements on the target device)? * Logcat says: "Display subsystem failed to initialize. check logs." - are there other logs than logcat I could check; and if so, which are they? * Is there anything else I could try, to get this tablet to boot fully?