Repair broken Nebra indoor with eMMC failure

The first versions of Nebra indoor miner came with CM3 (Raspberry Pi Compute Module) embedding eMMC memory. As you may know, Helium has been really I/O intensive, particularly this summer when the blockchain was filling really fast the small amount of storage the CM3 has. As a consequence, all my Nebra indoor miner dead around the same week. Diagnostic seemed to be a storage failure.

Here is the story about making them live again

Get a new CM3 board

The easiest way was to replace this part. The normal price for a CM3 is about 40€ even less for a CM3-Lite… unfortunately, one problem hide another, and with chip shortage, there is no more CM3 on the market. In fact you can find some… for the price of a full equipped PC computer. Makes non sense to buy some to repair a helium miner at this price.

Fortunately, I had in my stock a CM3-Lite, this is the equivalent of the CM3 in my miner but without storage on it. It’s also the equivalent of what more recent Nebra miner have. So, once I’ve got the firmware from Nebra (thank you for them, it as been simple and fast to get it), I just had to flash a SDCARD, put it on the Nebra board slot and start-it again.

Flash a CM3-Lite RPI on a nebra

For flashing the CM3-Lite on Nebra Indoor miner, plug a serial cable on programming interface, switch the jumper to the programming position and insert a SDCard on the slot. Then you can use a software like Balena etcher to flash it. The compute module and the associated SDCard should be visible.

That was the simple way, when you get spare parts !

Have more fun with original CM3 transformation to CM3-Lite

Unfortunately, if you don’t have a spare CM3 it’s hard to find some and the best way i found was to transform a CM3 into a CM3-Lite … with some help of my solder iron ! For sure, it you follow my experience, do it at your own risk, this may be never save your miner, may be kill your CM3 forever… In my case, I’ve been rescuing my Nebra.

STEP 1 – remove the eMMC chip

This step is the more difficult, you need to have a hot air soldering station to remove the eMMC chip. It’s better to have the air flow in the center of the chip as all the bga balls are located in the center and not around.

Remove the eMMC chip with hot air soldering station

Once you get the chip removed, now, you need to re-route the signal to the extension board, like a CM3-Lite does. The PCB for both model is the same, so you just need to remove 2 resistors and short-cut some missing resistors.

Convert CM3 to CM3-Lite

On the top side of the board, you need to first remove the resistors R10 (RED) and shortcut the resistors in blue (R16, R17, R18, R19, R9, R12) shortcut can be made with soldering materials easily (BLUE). Like you can see above:

The last step is to make the same on the bottom side where you have to remove R24 (RED) and shortcut R25 (BLUE)

Convert CM3 to CM3-Lite

Once this done, you have a CM3-Lite board and you may be able to flash and boot on a SDCard with it. That way I resumed my second Nebra.

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