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Use this guide to calibrate a Kobo eReader E ink display. This is done by changing the VCOM number, or "common voltage" number in your Kobo eReader to match a new motherboard or new E ink screen.
This guide works with the Kobo Libra Colour, Clara Colour, and Clara BW (both N365 and P365) models.
The VCOM number is the reference voltage associated with the device's screen. In order for your screen to work properly, the stored value needs to closely match the VCOM number printed on the screen. You'll need to change the VCOM number if you replace the screen or the motherboard.
Changing the VCOM number is only recommended during display or motherboard repairs. If the motherboard's stored VCOM number doesn't closely match the VCOM number associated with the connected E-ink display, you might see ghosting or a fuzzy / unclear picture. If the VCOM numbers stay severely mismatched for long periods of time, this may result in permanent damage to the E-ink display.
Note: The VCOM value displayed in Settings may not match the inputted VCOM value to the exact digit.
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Check the display cable for the three digit VCOM number.
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If your screen doesn't have a printed VCOM number, scan the QR code with a dedicated QR scanner app to generate the number. Your smartphone's built-in camera app might not work.
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The VCOM number registered on your eReader will be this three digit number multiplied by 1000.
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From the home screen, select More at the bottom right corner.
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Select Settings.
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Select Device information.
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Find the row titled Firmware information and select View.
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The VCOM number will be listed on the popup. Compare it to the VCOM number for your screen.
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If your VCOM numbers match, your screen is already calibrated—you're done! If the numbers don't match, follow the next three steps to change the VCOM number.
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Plug your eReader into a computer.
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You'll be prompted on the eReader that a computer is detected. Select Connect.
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If you're having trouble connecting to your computer, click here for troubleshooting information.
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On your computer, use a text editor to create a .txt file named vcom with only the desired VCOM number (including the negative symbol and the x1000 multiplication).
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Find the drive called KOBOeReader and open it.
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Move the vcom file into the drive.
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On your computer, eject the eReader.
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Once the device successfully ejects, you'll be prompted to update the VCOM number. Select OK to update the number and restart the eReader.
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Navigate back to the Firmware information page and check if your VCOM number has updated.
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Calibration didn’t go as planned? Try some basic troubleshooting, or ask our Answers Community for help.
Calibration didn’t go as planned? Try some basic troubleshooting, or ask our Answers Community for help.
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Any way of doing this on a kobo nia? I just changed my cracked screen and I don't have the vcom heading, nor do the steps work for my model.
Cheers
I saw some posts on forums commenting that some users opened their Kobo and noticed that the VCOM indicated on the board was different from the VCOM configured in the system. My question is whether I should open my Kobo to check if my model also has a mismatched configuration. It seems that several devices are coming with them misconfigured, and here on iFixit, there is the following information: If the VCOM numbers stay mismatched for long periods of time, this may result in permanent damage to the E-ink display.
So, should I open it to check or ignore it, even though there is a possibility that my Kobo is misconfigured? Any suggestions from Kobo or iFixit regarding this?
Hi, my reader's VCOM value is -1352mV and I've tried to open the back cover to check my VCOM number and found -1.36, I changed to the new value and "upload" to my reader like your procedure, but every time I reboot my device and found the value changed nothing, remains -1352mV.
I'm making sure that each step is correct. Does anyone know what's the problem?
The VCOM values won't match to the exact digit. In your case, they're super close together and won't pose a problem.
What variance/difference is considered acceptable? My device firmware info tab lists -1470 however the inside of the device via QR code lists -1.48.
That's within tolerance and won't pose any problems.
I wonder if there is some battery life variances caused by this? My Kindle Libra color is at 1.64v. Then you have another user all the way at 1.25v. that's 390mv which seems pretty significant since if backlight it as zero the screen power might be a decent affect? But that's quite hard to test for without units with different voltages in hand.
Or maybe a higher number is better since it's -xxxxmv? Would be interesting to know at least.
Demon09 -
I have a Tolino Vision Color, changed the LCD and it is working great. My old LCD was -1.70 and the new one is -1.45. There is no ghosting or any other problem.
But I switched my Tolino to Kobo, now the latest Kobo version is installed, but if I upload the file vcom.txt with the new value to the eReader, nothing happens after disconnecting the device. Under Software Details, I also don't see any VCOM value displayed. Only Waveform, Kernel Version, Touch Firmware, Status Code and Bluetooth Firmware.
Can I change the vcom value in the DEV mode? If yes, I need to reinstall everything from scratch. Or what can I do, to solve this?
There is a procedure to switch from Tolino Software to Kobo Software using the DEV mode.
Klaus -
For Tolino Users (Clara / Vision Color)
If you want to change the vcom value, you have to switch to the Kobo Stock 4.x firmware. Then the vcom.txt file will be accepted and the value will be changed.
Steps:
1. Search for "github notmarek" and on github look for his project "KoboTolinoFindings"
2. Connect your eReader to your PC using the USB cable
3. Copy over the file Kobo.tgz to the eReader under .kobo/ (If you don't see this folder in your file browser, enable hidden files)
4. Disconnect from USB, eReader will perform a reboot
5. Developer Mode is now activated
6. Copy over the file update.tgz from the PATH DowngradePackage to the eReader under .kobo/
7. Disconnect from USB, eReader will perform the downgrade
8. Check, if you can see the vcom value under Firmware Information.
9. If yes, you can proceed with the above mentioned steps.
10. As soon as you have WiFi, the eReader performs an update to the latest Kobo Stock 4.x version.
Klaus -
