Stuck Rainbow Screen

[polmdm]

Hi,
yesterday after one year of service, my RPi3B+, after a current drop won't start anymore, the sd fortunately still works and I've moved it to RPi4.
Anyway I've taken another SD and flashed with raspbian but the RPi 3B+ won't boot, so far I've tried to connect to a screen and actually the only think it does is to show the rainbow screen. Moreover the green led flashes 5 times slow and 4 times fast that's really strange. The same SD, inserted in another rpi 3b works and I took the opportunity to update it and update kernel but putting back to b+ the issue won't resolve. I've also tried to add "boot_delay" but again with no success. Even trying others images etc seems to fail. Since to 3V3 is connected a fan and actually it works I have reason to believe that the rpi isn't broken.

Any suggestion?

[DougieLawson]

Get a fresh new SDCard and the Raspberry Pi Imager tool. Use the imager to write a new copy of Raspbian on the new SDCard.

Boot that.

Get a USB SDCard reader, insert the broken SDCard in the reader, insert the reader in your RPI and use the new Buster system to repair the damage (or collect important programs, data and photos from the broken system (before your reformat it)).

[polmdm]

Okay but even a new SD won't boot, I've flashed a new one with raspbian-buster-lite but on that RPi won't boot.
Actually I'm not interested in saving the contents of that SD, I want only to recover the functionality of my RPi

[DougieLawson]

Have you measured the voltage between pin#1 and the outside case of the USB? Have you measured the voltage between pin#4 and the USB?

If the first measurement is not 3.3V when the second measurement is 5V then you've blown the PMIC off the face of the planet and your RPi is headed for the WEEE recycling.

[polmdm]

Yes, I've done it and both 3V3 and 5V are okay.

It's worth to notice the GREEN LED blinking, looking better:
5 long blinking - 5 short blinking and stuck at rainbow screen

[davidcoton]

Try without the fan?
3V3 is not intended to supply much power, and is susceptible to noise injected into the Pi.

[polmdm]

Yes, I've also tried to get rid of the fan but the rpi still won't boot. Actually I've mounted the fan one year ago and it have never gave issues to my rpi. The strange thing is that the same SD on a RPi3 with the same fan work properly....

[B.Goode]

There is a summary of all the knowledge accumulated from these forums during the past 8 years about difficulties getting an RPi to boot, see - STICKY: Is your Pi not booting? (The Boot Problems Sticky) - https://www.raspberrypi.org/forums/view ... 28&t=58151


A partial failure of the sd card reader on the suspect RPi is one possible diagnosis.

[polmdm]

I've read the entire article already and tried all the possible solution. I don't think that a failure of sd card reader is the issue since up to rainbow screen it boot, this means that the rpi read the sd. Right?

[davidcoton]

IIRC the SDCard slot mode changes after the rainbow screen boot, something like using 4 bit transfers instead of single bit. So it is possible.

[B.Goode]

IIRC the SDCard slot mode changes after the rainbow screen boot, something like using 4 bit transfers instead of single bit. So it is possible.

^__

What he said. Which is why I made the suggestion. Mentioned in the Sticky post cited.

[polmdm]

Okay, now it make sense, but now I have 2 questions:
How can be broken if the raspberry hasn’t experienced any “physical damage”?
There are any way to fix it?

The pins seem fine...

PS. In the guide that behaviour is described only for RPi 4 and not RPi 3b+

Futhemore making the sum of long and short green led blinking I got 8 blinks this means that the issue can be addressed to sdram but I've just downloaded the latest version of raspbian so everything should be updated....