(Partially) Repairing a Super NES Classic

My friend’s SNES Classic stopped responding to controller inputs. He reset it to factory settings but couldn’t even get through the language selection menu without being able to push buttons.

I told him I could take a look.

First I used Hakchi to save a backup of its internal storage.

Then I flashed the factory kernel and system software and erased the user partition. Same thing. Controller did nothing.

I tried my own controllers to no avail. And his controller worked in mine, so the issue was with the console itself.

How do we debug further?

The SNES Classic runs Linux on a somewhat mainstream ARM A7 SOC by Allwinner, and if you use Hakchi to flash its custom kernel, you can telnet to the device while it’s running and interrogate it.

Unfortunately, I didn’t keep great logs of this part of the process, but eventually I noticed something suspicious in dmesg:

[    -.------] twi_start()434 - [i2c1] START can't sendout!

That message comes from the Allwinner SOC i2c-sunxi kernel driver in /drivers/i2c/busses/i2c-sunxi.c.

Oh no, an I²C start packet timeout sounds more like a hardware failure than anything my friend did with Hakchi. The SNES Classic controllers (and all Wii Nunchuk connectors) communicate with I²C (or TWI if you prefer that name). It’s time to pop open the case.

With the case open and the heatsink off, there’s not much to it.

The unshielded board with labeled components.

The SOC is a four-core Allwinner R16 with a Mali GPU. It’s quite a capable little chip.

You can also see the DRAM (Nanya NT5CC128M16IP-DI), flash (Macronix NT5CC128M16IP-DI), and PMIC (X-Powers/Allwinner AXP223) on the top of the board. The HDMI circuitry (Explore EP952) is on the bottom.

Most of that’s irrelevant - the important part was whether I could find anything wrong with the I²C signals between the connector and the SOC.

I won’t bore you with all of the random stuff I probed, but I eventually noticed that controller 1’s SCL line had a low-impedance path to ground, about 670 ohms. SDA and both of controller 2’s signal lines were pulled low at 1 MΩ, which makes a lot more sense.

Having the clock incorrectly pulled low would explain why it couldn’t communicate with controller 1. So where is the fault? It’s either somewhere in the PCB (unlikely) or in the SOC’s I²C buffer.

If the PCB, that’s easily fixable: cut traces and bodge a wire from the closest good point. If it’s in the SOC, that’s something I can’t fix. I don’t have the skill to reball and resolder BGA. While you can easily acquire an Allwinner R16 on Alibaba, there’s no way I could reball and solder it to the board without breaking something else. I did find a service that does BGA rework but it starts at $200 and the SNES Classic isn’t worth that much.

It was a little hard to trace the path from the connectors to the SOC because the traces run on inner layers. Eventually, I found some jumpers to desolder to isolate the fault.

I desoldered SCL1’s jumper – well, let’s be honest. I melted that tiny sucker into a black paste while struggling to apply even heat. Unfortunately, SCL1’s short to ground is in the chip and I can’t fix that.

At this point, software fixes became the only option.

I was wondering if you could patch the Hakchi kernel to swap controller 1 with controller 2. It may not even be hard. Then at least one controller would function.

But I also saw someone on Reddit mention that the system supports receiving power over USB while acting as a USB host with a powered USB On-The-Go cable. You can build your own O2G cable with wire snips, a soldering iron, and heat shrink tubing. I just purchased one from Amazon instead. The reviews make it clear this is a popular purpose for the cable.

The stock Nintendo kernel does not support USB controllers but the latest Hakchi kernel does! I confirmed an Xbox controller can navigate the menu and every button works in game. Even better, controller port 2 still works as usual!

I wonder if raphnet’s Classic to USB adapter would work so you could keep the SNES controller experience.

At this point, I declared as much victory as this was going to get and sent it back to my friend. It’s nice to keep quality hardware out of the e-waste bin.