VU7/7+ only working with hot reboot or replug of hdmi cable

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senn
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VU7/7+ only working with hot reboot or replug of hdmi cable

Post by senn »

I have an issue with VU7/+ : screen remains black with cold reboot
(shutdown -rh), goes alive with hot reboot (shutdown -r, ctrl/alt/del) or
unpluging/pluging the hdmi cable. Other Hdmi monitors work fine.
OS image is ubuntu-20.04-5.4-minimal-odroid-xu4-20210112.img (with boot.ini
from ubuntu-18.04.3-4.14-minimal-odroid-xu4-20190910.img).
Have you already faced this problem ?
Thank you

éric

senn
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Re: VU7/7+ only working with hot reboot or replug of hdmi cable

Post by senn »

I found the source of the problem.
The VU7+ is powered by one of the XU4 USB socket. This USB socket apparently
does not provide enough current at 'cold' boot time.*
Indeed, when I connect the VU7+ USB power cable on a USB socket from another
device, say my laptop for instance, this 'blank screen' problem disappears.
I have checked with another XU4 board, running an Ubuntu 16.04 image, powered by
fully loaded batteries : same problem.
As a conclusion, let's say that the XU4 USB power lines are a little "touchy" ...
especially at startup.

*I am currently using a regular 5V/4A AC/DC power supply.
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Re: VU7/7+ only working with hot reboot or replug of hdmi cable

Post by odroid »

Do you use this PSU?
https://www.hardkernel.com/shop/5v-4a-p ... us-plug-2/

Is there any other USB devices plugged to your XU4?

senn
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Re: VU7/7+ only working with hot reboot or replug of hdmi cable

Post by senn »

No, my power supply is not the one you show in the picture.

I have taken a picture of mine but don't know how to add it to this post.
Its spec are :

Brand : CWT
MODEL: KPC-020B 20W
INPUT: 100~240V~50/60Hz 0.8A
OUTPUT: 5.0V DC 4.0A

Yes, there was a keyboard and a wifi dongle on the two other usb sockets of the board.

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Re: VU7/7+ only working with hot reboot or replug of hdmi cable

Post by odroid »

XU4 eats up to 3Amp in the booting process and Vu7 needs around 1Amp.
If the PSU has no spare margin, your symptom seems to be normal.

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