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I have 2 Raspberry`s (Raspberry Pi 3 B+).

One is working fine and well and if I want to turn on my other Raspberry Pi(with the same SD Card what I used for the other) the ACT LED is just blinking 4 times and wont boot the Raspberry Pi.

I checked and 3v3 and 5v is there.

I tried 2 types of Adapters 5v 1A and other other is 5v 2A and with both Adapter was working fine (just 1 raspberry) and the other Raspberry Pi was still not working :(

My question is what could be the problem that it wont boot?

Regards

Milan

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    The regular blinking pattern indicates a problem with what is in the boot partition. So the card is at least recognized but the contents are possibly corrupt; since the boot partition is readable from pretty much any computer, you should have a look at that. The number of blinks in the pattern do indicate something, unfortunately AFAICT the Foundation has still not bothered to document this (they've only had about a decade)...
    – goldilocks
    Feb 3, 2022 at 14:58
  • ...and the only existing source I know of is out of date: elinux.org/… Since according to that 4 blinks = bad/missing loader.bin, which is no longer used to start with.
    – goldilocks
    Feb 3, 2022 at 14:59
  • Pi boot sticky forums.raspberrypi.com/viewtopic.php?t=58151
    – CoderMike
    Feb 3, 2022 at 16:09
  • since you've tried both identical pi's with the same sdcard and same power supply, and one works and the other doesn't, this suggests there's nothing wrong with power supply or the sdcard (not sure why everyone is linking to the normal boot problems links - they hardly seem relevant in your case) - visually inspect the insides of the sd card slot - comparing the two pi's - do they look the same?
    – Bravo
    Feb 4, 2022 at 0:08
  • another thing to try is to boot from USB (the 3b+ comes with the ability to boot from USB out of the box) - then insert an sd card into the slot and see if it can be read
    – Bravo
    Feb 4, 2022 at 0:09

2 Answers 2

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Most such can be resolved by The Boot Problems Sticky
There is a separate Pi4 Boot Problems Sticky

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I experienced a similar problem when trying to run the 2020 raspbian images on a recently manufactured Pi 3B+. Black screen, refused to boot, only blinking green ACT light.

This Pi 3B+ was purchased in Nov 2023. Since the 3B+ first retailed in 2018, I was expecting a 2018/2019/2020 raspbian image to work on this Pi 3B+ without a problem. I was wrong. The hardware manufacturers have broken compatibility with these raspbian images by installing new types of SDRAM chips on recently manufactured Pi 3B+ boards. Newer firmware is needed to operate these chips.

So, it is impossible to boot a recently manufactured Pi 3B+ with the firmware from a 2018/2019/2020 raspbian image. All you get is a black screen. The green ACT LED blinks like so:

  • 1 blink
  • Wait 1 second
  • 4 slow blinks
  • 8 rapid blinks
  • Wait 1 second
  • Loop forever

If you are experiencing this problem, you can resolve it by replacing some firmware files from your older raspbian image with their equivalents from a newer raspbian image.

  • Replace all /boot/fixup*.dat files
  • Replace all /boot/start*.elf files

For example, in my case, I was trying to run the 2020-12-02 raspbian release on this recently manufactured Pi 3B+. Only after I replaced the noted firmware files with their equivalents from the 2023-05-03 oldstable release did it finally boot successfully.

Credit to user Dougie for sharing this solution in a comment to this question: Raspberry pi 3b+, 3 green flashes, no display at all

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