Aura HD Modifying VCOM for refurbished device

[MarkWilliams]

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]

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

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

[MarkWilliams]

Originally Posted by ratiz

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

[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.