Aura HD Modifying VCOM for refurbished device

MarkWilliams · 09-12-2026, 06:40 AM

I have an official Kobo refurbished Aura HD. I don't know if the screen was replaced or not, but screen contrast is poor compared to my Mini. I notice than on images I cannot see all the grey levels.
I wonder if the VCOM level has been set correctly so I open the device and checked the label, which is -2.20 .

I inspected the appropriate bytes in /dev/mmcblk0 but they were set to 00, so I changed them to FF24, which corresponds to -220. I can verify the change with ntx_hwconfig but the contrast does not appear to improve after a reboot.

Should I modify the values further, or try a different approach. Is it possible to verify the waveform?

ratiz · 09-12-2026, 06:45 PM

I don't know if that helps but here are the values I have on my Clara Colour.

Code:

[root@kobo ~]# ntx_hwconfig -S 1 /dev/mmcblk0p6 -l | grep -i vcom
[39] VCOM_10mV_HiByte=0xFE
[40] VCOM_10mV_LoByte=0xE2

MarkWilliams · 09-13-2026, 09:25 AM

Quote:

Originally Posted by ratiz

I don't know if that helps but here are the values I have on my Clara Colour.

Code:

[root@kobo ~]# ntx_hwconfig -S 1 /dev/mmcblk0p6 -l | grep -i vcom
[39] VCOM_10mV_HiByte=0xFE
[40] VCOM_10mV_LoByte=0xE2

That equals -286 or -2.86 Volts. I would guess that colour screens use larger values.

MarkWilliams · 09-15-2026, 03:57 PM

I changed the VCOM to -200 and noticed no difference. I then changed it to -249 and I can see a marked improvement in contrast on text and images. I am going to leave it as that for a while.

09-12-2026, 06:40 AM	#1
MarkWilliams Junior Member Posts: 7 Karma: 10 Join Date: May 2015 Device: Kobo Touch	Modifying VCOM for refurbished device I have an official Kobo refurbished Aura HD. I don't know if the screen was replaced or not, but screen contrast is poor compared to my Mini. I notice than on images I cannot see all the grey levels. I wonder if the VCOM level has been set correctly so I open the device and checked the label, which is -2.20 . I inspected the appropriate bytes in /dev/mmcblk0 but they were set to 00, so I changed them to FF24, which corresponds to -220. I can verify the change with ntx_hwconfig but the contrast does not appear to improve after a reboot. Should I modify the values further, or try a different approach. Is it possible to verify the waveform? Last edited by MarkWilliams; 09-12-2026 at 01:23 PM.

09-12-2026, 06:45 PM	#2
ratiz Junior Member Posts: 6 Karma: 10 Join Date: Sep 2026 Device: Kobo Clara Colour	I don't know if that helps but here are the values I have on my Clara Colour. Code: [root@kobo ~]# ntx_hwconfig -S 1 /dev/mmcblk0p6 -l \| grep -i vcom [39] VCOM_10mV_HiByte=0xFE [40] VCOM_10mV_LoByte=0xE2

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09-15-2026, 03:57 PM	#4
MarkWilliams Junior Member Posts: 7 Karma: 10 Join Date: May 2015 Device: Kobo Touch	I changed the VCOM to -200 and noticed no difference. I then changed it to -249 and I can see a marked improvement in contrast on text and images. I am going to leave it as that for a while.

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