Using the same exact SD Card and USB stick with the newest version of Raspbian I have one Raspberry pi 3B+ that will only Flash 4 times when trying to boot and no rainbow screen, where as with another IDENTICAL Setup that System boots fine. Suggestions to what is wrong with the 'broken' pi and ways to fix. EDIT (So I dont understand why this is marked duplicate all linked Questions reference a single failure regarding the SD Card my Question is I have two Raspberry pis one works with an SD Card and Usb to boot while the other does not with the same Setup so the SD Card and Usb are not the Problem what is?)

  • You puzzle is interesting. Let me see what I can try now. Any brain storming suggestions welcome. I also have Rpi3B+ with Raspbian 2019Apr. The first thing I am going to try is to lower the Rpi PSU from present 5.25V down to about 4.5V (I have a PSU that has manual push buttons to adjust outputs voltage by very small steps.) I suspect that even if you use the official Rpi PSU, that might be marginal and blinks too low when booting up. It might be so marginal and affects one "identical" guy but not the other. :) – tlfong01 May 20 '19 at 6:50
  • Questions (1) Have you tried only one or two SD cards? Can you tried more? Your present SD cards may be just marginally good, so the good rpi with "stronger" reader can read, but not the other weak Rpi. (2) Are you using noob? Noobs have more problems than full versions. For noob, you need to FULLLY FORMAT the SD card, using SD Formatter 4 or 5. – tlfong01 May 20 '19 at 8:57
  • I have formatted the Card with SD Formatter 5 before installing the full Version of Raspbian using windows32 disk imager. I have not tried a different SD but it is an 32GB Samsung EVO+ if that is of any help. – user4321 May 20 '19 at 9:34
  • Ah, let me see. (1) I have about 20+ micro SD cards in hand, about 40% 8GB, 40% 16GB, rest 32GB. I do find damage rate of 16GB cards very roughly twice as 8GB. Recently I bought 4, SanDisk, 4 Hitachi, 4 Transcend 16GB cards from a very reliable shop, all with bar coded serial number on paper receipt. I very surprisingly found that one of the 4 SD cards was problematic, (very slow, 4Mb/s, compared with other three, 10~20Mb/s. Your WinPC hardware USB sd card writer might also be marginally good. I direct plug my US$10 reader to PC, without cable. also SHA256... msg too long, stop here. – tlfong01 May 21 '19 at 2:38
  • You might also like to read my bad SD card probability and statistics in the references section of my answer. – tlfong01 May 21 '19 at 3:23


Two identical Rpi3B+ setups, "good" setup boots SD Card OK. The "bad" setup can only start booting to 4 green LED blinks, then stops.



I suspected your PSU is marginal, and when booting, drops to a low voltage much below 5V, and so any weird thing can happen.

So I tried using a adjustable PSU and see if Rpi can boot at a voltage as low as 4V. My PSU is has a huge 10,000 uF (yes, 10,000 uF!) bypass capacitor, so there should be almost no glitches or blinking when booting. I also checked with my 3.5 digit DVM to make sure the voltage very near Rpi micro USD connector is almost the same as the PSU.

I surprising found that Rpi3B+ can boot a stretch 9.8 SD card at 4V (I think there should every little chance that your official PSU blinks below 3V3), though with yellow lightning warning and text message saying low voltage etc.

My conclusion is that my guess was wrong. Even if your PSU drops to as low as 4V, Rpi's on board LDO regulator can very forgivingly accept and boots to the end with the welcome screen!

Any brain storming suggestions welcome.

rpi boot test

rpi os image record

Update 2019mayhkt1425 - Recommendation to use 16GB cards

A couple of years ago, 4GB SD card was "fast", expensive but most cost effective, so I bought 4GB to install Rpi Debian then, which was 2GB.

But now it is not a good idea even to buy 8GB SD cards, because they are usually very slow, comparing with 16GB cards. So I have upgraded to 16GB which I think it is most cost effective now (2019).

And as Raspbian stretch 2019apr full version image is "only" 5GB, so I guess there is plenty of space for a hobbyist programmer like me. I have been doing Micky Mouse projects for a couple of years, and all the python programs added up to only a couple of hundred MB.

I am using Rpi3B+ and I think there is almost no speed difference if I have biggest or smallest version, if I used a 16GB SD card.

To summarize, I don't bother to consider which is the best size of SD card. I think 16GB card installing the biggest Raspbian stretch version is best for a hobbyist python programmer like me.

I also keep a record of the SD card speed/price and serial numbers (in case I need to complain or ask for replacement. You might like to see my 2019 record.

sd card purchase record


SanDisk Ultra SD Card with Raspberry Pi 3+ Suddenly Stopped Working (and is Overheated!)

What is the best way to copy the whole rasbian image?

Raspberry Pi 3 Model A+ Faint green pinprick light steady flashing

Appendix A - Why 16GB card is "better" that 8GB?

  1. I am 100% sure that your two "identical" Rpi setups are not truely identical. Even if you have only one Rpi, your Rpi setup yesterday is not identical to your setup today.

  2. The problem now is to find out which part or parts of two seemingly identical Rpi setups are not identical.

  3. There are 101 possibilities that make two Rpi setups not identical. Let me list one by one.

  4. Perhaps one Rpi has "bright" eyes than another. So even if the SD card has very slightly "blurred" characters, the bright eye guy can detect that a blurred character looking like big "C" is indeed a big "G". The poor dim eye guy cannot notice anything, and happily reads on, ...

  5. Now the Windows Image guy writes characters on the piece of "paper" stuck on the SD card. The 16GB card has a piece of paper not too much bigger in size than the 8GB one. So the WinImg guy writes smaller characters on 16GB paper, and bigger characters on 8B paper.

  6. The result is that big characters even blurred, can be easier detected by whether bright or dim eyes.

  7. Conclusion: 16GB is better than 32GB.

Actually there is also a couple of other reasons why 16GB is better than 8GB. In other words, 16 going on 17 is the most beautiful among 3 sisters, ...

| improve this answer | |
  • Is there any reason why using a 16GB would make a difference between two identical PI's? – user4321 May 21 '19 at 7:54
  • Yes, read the Appendix A just added. – tlfong01 May 21 '19 at 8:36
  • Interesting I will get a 16Gb and try that out instead, I would have assumed that same product = same Performance but it seems that this is partially wrong from your Explanation so the path now is to figure out what part of the board is now acting differently? – user4321 May 21 '19 at 9:01

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