Intro
In April 2023 I finally got my Turing Pi 2 - happy to finally got it into my hands I plugged it in, headed over to the Turing Pi 2 Github ( https://github.com/turing-machines/BMC-Firmware ) got myself the latest BMC firmware and started to flash it. Thats when things got wrong: The power supply coils started to screech - and seconds later I was greeted with blue smoke and a dead Turing Pi 2. The firmware update actually flashed the board into a paper weight.
The one green led was still on, the BMC led was off and the board did not react - also the networking LEDs were off. To be honest, this was the first time a firmware update actually physically bricked hardware / got it up into smoke.
Luckily, Turing Machines, the company behind Turing Pi 2 did send me another board, thinking that the (also ordered at Turing Machines) small form factor power supply could have been the culprit - thanks a lot guys for that tremendous help!
The new board was working without an issue and did wait for quite some time until I updated it - horrified the same thing could happen again. I think I updated it to 1.1.0 and things were ok back then.
However, with half a year passed and still the dead board lying around I thought, maybe I could fix it?
The incident
What happened was a short circuit - but how? The only thing I could think of was an error in the firmware upgrade - and the BMC processor - a dual core Allwinner T113-S3 - shortcircuiting something as it did not have its initialization correctly. While this should never be possible (e.g. that a board is layouted in such a way that a processor would short-circuit if it has no program available), I had no other explanation. But how to find out what was broken? The incident actually burned the 5A SMD fuse for the 3v3 line - meaning the board was now powering up ok-ish, but without any of the 3v3 components (e.g. the BMC). Short-circuiting the fuse directly lead to warmth and a bad stench - something was still short-circuiting. So I build myself a Thermal Camera. I was quite sure that the T113-S3 was toast by now, so I removed it.
After that, I tried bridging the blown fuse again - this time with an ampere meter. About 6 Watts were going somewhere I did not know. The Thermal Camera showcased an SMD capacitor glowing red - that poor thing got mangled so badly that it decided to become conductive for DC - not good. I removed that capacitor as well - no excess power was drawn anymore after that.
The repair
I ordered two new Allwinner T113-S3 ( T113-S3 ELQFP-128, position 2 on the picture below ) as well as some spare 5A SMD fuses ( LF5A - 10PCS/LOT 1808 SMD fuse 125V fast 5A, position 1 on the picture below ) from the web. The capacitor with 570uF was replaced by a 12.2uF for testing ( position 3 on the picture below).
As soon as I had everything in place, I got the latest firmware image, 2.0.5 from the Turing Pi Website ( https://firmware.turingpi.com/turing-pi2/v2.0.5/tp2-firmware-sdcard-v2.0.5.img ). I flashed it onto a MicroSD Card with balenaEtcher and inserted the MicroSD Card into the appropriate slot on the backside of the Turing Pi 2. With everything in place, I hooked everything up, got myself a flathead screwdriver and shortend the MOSI and SCLK/Clock lines of the flash module on-board of the Turing Pi 2 as mentioned in this issue ticket: https://github.com/turing-machines/BMC-Firmware/issues/134 ( see position 4 in green, the left bottom two legs of the chip ). You can also see the both legs better on the picture below:
With my screwdriver still shorting both legs of the flash module, I applied power to the Turing Pi 2. After some seconds, the LEDs came on and the 4 LEDs of the ethernet ports started blinking slowly. I removed the short-circuit on the flash module, pressed KEY1 3 times rapidly and the ethernet ports started turning on one LED at a time. After about 30 seconds, the LEDs stopped the animation and all LEDs blinked twice (again and again) to show the flash was a success. I powered down the Turing Pi 2, removed the MicroSD card and powered it up again - and it was fixed! 🙂
( Usual procedure for update from a MicroSD Card can be found here: https://docs.turingpi.com/docs/turing-pi2-bmc-v1x-to-v2x )
Good ending
With that, the Turing Pi 2 was fixed - BMC is answering my calls, all four nodes are working. It was not an easy fix by all means, but using a microscope, loads of flux and patience made it work again. And the Thermal Camera! That less than 40 Euro thing really helped a lot, otherwise I would have not found the issue without turning the whole board into a burning mess.
