Smartphone (Note 4) only starts at cold temperatures (and MicroSD MBR overwritten with “testnonce”)
A Galaxy Note 4 worked well until few days ago. When I returned after I left it charging as usual, it did not wake up from stand-by mode. Only the green LED light remained on. It being green instead of red indicates that the battery reached full charge. Usually, pressing Home+Power+VolumeDown and holding for 10 seconds forces a reboot, but it did nothing this time. The green LED even remained on.
After taking out the battery and inserting it back in, it did not start imminently, but after waiting few minutes before inserting the battery, it finally did start.
When not powered on, instead of no response, sometimes I encountered errors during start like "There is no pit binary" and "flash read failure" errors that even occured on the battery charging screen. The errors were written in the upper left corner of the screen. But in case of a successful boot, everything went fine while the device is running. Even the fast charging still works.
Upon further experimenting, I figured out that the device is more likely to start successfully at colder temperatures, e.g. after exposing it to a fan for minutes with battery removed.
When the device is in this unbootable state, it draws exactly 0.52 A of current from a USB charger with battery inserted and 0.15 A without battery inserted. I remember it only drawing 0.06 A with no battery inserted when everything worked fine.
While I found this XDA thread which might provide some clues, does any of you have a clue what might be causing this?
What would cause a mobile phone to only start successfully at cold temperatures?
Another strange occurance: The master boot record (first LBA) of the MicroSD card inserted in it got overwritten with the word "testnonce" that started at byte offset 0x01E2.
I simply repaired it in a HEX editor by taking the MBR from another identical and preformatted MicroSD card. But does anyone have a clue about what caused this “testnonce” nonsense? It appears to be something similar to "USBC".
That is in most of case problem with EMMC Life Time Estimation