noJD
Posts: 4
Joined: Fri Jun 18, 2021 11:03 am

does rainbow screen flicker hint at a poor power supply?

Fri Jun 18, 2021 11:17 am

Hi,
i have just got another rpi4 under warranty because the first one developed video problems after some 30 hours of use.
the rainbow screen started to become washed out of color and the desktop started flickering...shortly after it would not boot anymore.
i use the original rpi power supply and i have never seen the lighting symbol when it was running.

however, when i just started up the replacement i saw the rainbow screen flicker a few times.
and was wondering if this is normal for an rpi4?
or that i should suspect my power supply being faulty and possibly also destroying this one?

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
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Re: does rainbow screen flicker hint at a poor power supply?

Fri Jun 18, 2021 1:00 pm

I'd be more worried about the HDMI cable.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Working in the Application's Team.

noJD
Posts: 4
Joined: Fri Jun 18, 2021 11:03 am

Re: does rainbow screen flicker hint at a poor power supply?

Fri Jun 18, 2021 3:56 pm

what about the hdmi cable? how would that wash out colors at startup and destroy the pi's video or cause the screen to blink twice or trice at the rainbow screen but no longer when booted to the desktop?

i have not seen any artifacts and i would suspect blocks and stripes if there was something wrong with the hdmi cable, because as i understand that is a digital signal, not analoge. and i would not know what bit would have to fail to, for instance, increase brightness on all available pixels simultaniously so the colors wash out.

So the question that i still have is, do any of you RPI4B-8GB users see the rainbow screen flicker a few times when it boots and can I assume this is normal behaviour for the PI or am i the only one and should i try to find what is causing this?

jamesh
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Raspberry Pi Engineer & Forum Moderator
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Re: does rainbow screen flicker hint at a poor power supply?

Fri Jun 18, 2021 4:22 pm

I hadn't realised it recovered after the flicker on the rainbow. Probably it's all OK then if everything works after that.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Working in the Application's Team.

noJD
Posts: 4
Joined: Fri Jun 18, 2021 11:03 am

Re: does rainbow screen flicker hint at a poor power supply?

Fri Jun 18, 2021 4:37 pm

i assumed the same with the rpi that was replaced under warranty, that it was OK because everything worked fine after the desktop was loaded.
so, i would still like confirmation that a few blinks in the rainbow screen is normal for the rpi4b-8gb

because i am not sure they will give me another under warranty when my rpi starts to get a washed out screen again after a few days of use.
so i'd rather be sure instead of sorry.

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
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Re: does rainbow screen flicker hint at a poor power supply?

Fri Jun 18, 2021 4:44 pm

The chances of getting a Pi with exactly the same fault as a previous one are incredibly remote, so if this one starts doing the same as the other one, I would suspect something else, especially since washed out colours in not a fault I have heard of before. HDMI cable, the monitor itself would be the possible culprits.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Working in the Application's Team.

LTolledo
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Re: does rainbow screen flicker hint at a poor power supply?

Fri Jun 18, 2021 9:35 pm

I too will suspect the HDMI cable, and/or the HDMI port of the monitor/TV being used...

best to confirm by interchanging with another known good HDMI cable, or known good HDMI port on the monitor/TV.
also the OP can try applying contact cleaner* on the HDMI ports.

*for your safety, its advisable to apply contact cleaner with the device/cable not being powered, power only if confirmed dry...
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aBUGSworstnightmare
Posts: 3187
Joined: Tue Jun 30, 2015 1:35 pm

Re: does rainbow screen flicker hint at a poor power supply?

Sat Jun 19, 2021 6:17 am

My bet is that such flicker comes from the monitors scaler board

noJD
Posts: 4
Joined: Fri Jun 18, 2021 11:03 am

Re: does rainbow screen flicker hint at a poor power supply?

Sat Jun 19, 2021 7:31 am

i have tested a different cable to no avail. will test a different monitor later today and let you know.

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