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I have a Samsung Galaxy S3, purchased on July 2012.

Sometimes, when I press the power button, the screen keeps black. The button LEDs turn on, but nothing else happens, and I have to remove the battery, or hold the power button for 20 seconds to force a reboot. It has happened to me 4 times; the first 2 were quite distant in time, but the last 2 were both this week.

Also this week, the phone has started to reboot itself. That has happened three times, two of them while I was using it, and the last one tonight, with the phone being idle (no wifi, no data connections, nothing). It just reboots automatically and then everything works fine.

I've never flashed the device, it's not even rooted. It's running Android 4.1.2, as I've installed all the official updates via OTA (base I9300XXELLA, kernel 3.0.31-836582, compilation number JZO54K.I9300XXEMA2). And no, I did not install recently any app which may be causing my problems.

So far, I've retired the microSD card (32GB card, manufactured by Samsung), because I've read that this may be the cause of the reboots. I'll try keeping it without the card for a few days. Although I've been using the same card for 5 months, and the reboots didn't start until this week. Edit: OK, we can rule out the SD card as the source of the problems - the phone also reboots itself without the microSD.

There are a lot of posts from people with similar problems, and most of the answers say they should try a factory reset. However, in most of the cases that doesn't seem to solve the problem. So, I didn't try it... yet. Maybe I should, but I'm afraid that the problem will be still present, and it's a lot of trouble for nothing.

I've already contacted with Samsung customer service, but in the meantime, is there anything else I can do?

Can I at least diagnose somehow what's happening? I've read here about something called logcat, however they say the log is only kept on memory, it's not stored, so it would be of no help to determine what happened after a reboot or a black screen problem...

Any ideas?

Edit: the phone rebooted itself again, and this time the microSD card was not inserted. That means one suspect ruled out, but I still have to find the culprit.

Edit: it seems that the problems were solved after doing a factory reset. At least, the phone hasn't rebooted itself for the last 5 days...

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  • If you feel it's worth the money, get yourself SystemPanel App / Task Manager (yes, there's also a free version -- but for this, you need the full one). The full version monitors your system in background and stores all collected information, so you can even watch it after a reboot. Try the free one first with "live monitoring" to see what information is available and if it suits your needs.
    – Izzy ♦
    Mar 16, 2013 at 12:36
  • Thanks for the help, Izzy. But that app seems to collect only data related to CPU and memory usage, network activity, battery consumption... Could be useful if my phone had a bad performance, or the battery life was abnormal, but that's not the case, the phone works great (until it stops working and/or reboots itself). What I need is something like a system log where I can read what exception caused the reboot/crash. Or, even better, somebody who had this same issue and managed to solve it... :)
    – AJPerez
    Mar 16, 2013 at 21:31
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    Yeah, that's of course correct. My idea was it can at least show you which app(s) where "quite active" when it happened, so after a couple of times a pattern might become clear. So another idea would be to permanently capture logcat to your SDCard (say in files using a timestamp, each day a new one, so you can cleanup easier and also pick the interesting ones). Logcat Extreme would be a candidate for that, recording the logcat in background.
    – Izzy ♦
    Mar 16, 2013 at 21:52
  • Just found: SaveLogCat even uses timestamped file names.
    – Izzy ♦
    Mar 16, 2013 at 21:57
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    Oh -- that problem with only seeing its own log entries (why do I always think that started with 4.2?)... In that case, it only leaves adb logcat if you want to go that way. Permanently hanging on a USB cable might be no option, which would turn this down as well (unless wireless ADB is possible without root)...
    – Izzy ♦
    Mar 19, 2013 at 11:52

2 Answers 2

Reset to default
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I found that the battery in my phone was a little smaller than the battery holder in the S3. It seemed that my phone would reboot or just turn off with just the right shake. I put a small piece of duct tape in the holder at the opposite side of the battery contacts to make the holder have more of a press fit with the battery. Problem solved for me!

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I gave up and did a factory reset. Since then, the phone has been working for 5 days in a row... so it seems like at least the reboots are gone (I hope not to jinx it...).

I've also noticed that since the reset, the battery lasts at least twice longer than before. I've fewer installed apps, which should lead to a slight battery life improvement, but this isn't slight, it's the double. Before the reset, at night (no data connections, no WiFi), the phone consumed about 1% of its battery per hour. Now it's consuming less than 1% in the whole night. Obviously there was something wrong before the factory reset. I hope everything is fine now...

In case it's helpful for anybody else, this what the Samsung Customer Service told me to do:

  1. Start the phone in Secure Mode for a couple of days. That means that only preinstalled apps will work. So if that solves the problems, there is an app causing them. To enable Secure Mode, you have to reboot the phone, and press the options button (the left one) when the Samsung logo appears; it should vibrate, and then you will see "Secure Mode" at the left bottom corner. To disable Secure Mode, turn off the phone and extract the battery for a few seconds. --- For Verizon GSIII phones: after you reboot the phone, press and hold the volume down button when the Samsung logo appears. Directions also state that you may need to hold the button for up to 45 seconds before you will see "Safe Mode" in lower left-hand corner. http://support.verizonwireless.com/support/devices/knowledge_base.html/59242/

  2. Perform a factory reset (if the phone still has problems running in Secure Mode). To perform it, go to Menu > Settings > Backup & reset > Factory data reset. It will revert the phone to its original factory status, therefore, you will lose all the data and applications stored in your phone's memory (it will not affect the SIM card, nor the microSD if you have one). Be sure to backup everything you don't want to lose! You can use Samsung KIES for that backup.

  3. If the phone still has problems after the factory reset, it should be checked by Samsung Technical Service.

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