PW3 Paperwhite 3 Behaving Very Strangely

[sedme]

I recently decided to jailbreak my Paperwhite 3 because I haven't used it very much in a while, and I figured I'd be able to get a bit more use out of it. Anyways, it was on too new of a firmware version (5.10.1.1), so I couldn't use a totally software-based method, I had to do a serial mod. I'm not very good at soldering, so I screwed up quite a bit at first. I tore a solder pad off so I had to find an alternate point of access compared to normal, specifically points TM800 and TM801 on the back of the motherboard. Since I'm uncomfortable soldering to tiny pads, I decided it would be a bright idea to solder to some RF shielding. When I finished with the jailbreak, and I was desoldering the wires, I spilled a little bit of flux around the RF shield. Specifically, it got around near where the SIM card would go. I cleaned it up the best I could, but I suspect some got in the RF shielding. At first, everything was fine, but of course, once I got the kindle fully reassembled and was messing around with SSH, it reset and got stuck on the same screen indefinitely, with the LEDs going full blast. I decided to bust the thing open again and reconnect to the UART so I could see what's going on in more detail. The following is what I got from that.

U-Boot 2009.08-lab126 (Oct 12 2018 - 06:10:48)

CPU: Freescale i.MX6 family TO0.0 at 996 MHz
Temperature:   35 C, calibration data 0x5a05225f
mx6sl pll1: 996MHz
mx6sl pll2: 528MHz
mx6sl pll3: 480MHz
mx6sl pll8: 50MHz
ipg clock     : 66000000Hz
ipg per clock : 24000000Hz
uart clock    : 80000000Hz
cspi clock    : 60000000Hz
ahb clock     : 132000000Hz
axi clock   : 198000000Hz
emi_slow clock: 22000000Hz
ddr clock     : 396000000Hz
usdhc1 clock  : 198000000Hz
usdhc2 clock  : 198000000Hz
usdhc3 clock  : 198000000Hz
usdhc4 clock  : 198000000Hz
MMC:  FSL_ESDHC: 0,FSL_ESDHC: 1,FSL_ESDHC: 2
Board: Muscat WFO
Boot Reason: [ POR ]
Boot Device: NAND
Board Id: XXXXXXXXXXXXXXXX (I blanked these out since I'm fairly certain they're specific to my kindle and it's not really necessary)
S/N: XXXXXXXXXXXXXXXX
I2C:   ready
DRAM:  512 MB
Using default environment

In:    serial
Out:   serial
Err:   serial
Quick Memory Test 0x80000000, 0x1fff0000
Memory error at 80000000, wrote 00000000, read ffffffff !
POST done in 9 ms
Battery voltage: 4080 mV

Hit any key to stop autoboot:  0 
Unknown command 'panic' - try 'help'
uboot >

It acted like this for a few hours. I thought I bricked my kindle by frying the NAND chip, so I started writing this post and I got the urge to reset the processor in uboot to see what the battery voltage was after so long, but to my surprise, it booted normally! Then, after a few hours of normal operation, the same thing as before started happening. Anyone have any idea what could be causing this? My only guess is that there's flux under the RF shielding shorting something out, but I don't really have the skill or equipment to remove it without damaging anything.

[MrTick]

It seems like UART Rx is receiving some noise from somewhere...
Please try this: take a magnifying glass and inspect carefully the original UART connector you seem to break, check if the teared trace is not touching anything etc. Just in case take a really sharp scalpel and try to clean around the original UART connectors.

If that does not help you can try to disconnect the mainboard from all peripherals, remove it completely from the case (remove the sim card and anything you can disconnect) and submerge it in isopropyl alcohol for 5-10 minutes -> buy* 0.5L of IPA, pour it into a ceramic plate and put MB there.
This should help remove all flux residues without damaging anything further.

*as it's now used for disinfection IPA prices skyrocketed recently, but it still should be affordable