Boomer48

If you grounded the EA pin and it still comes up in SPI mode then either the chip is defective or the clone doesn't read the configuration pins at power-up. Given that all of those boards are built for SPI mode they might have just cut corners on the chip design.

The original one I got doesn't have any markings on the chip. The most recent ones I bought (February) are marked "MXP RC522" so they must be clones. Here is the eBay link for my most recent purchase: https://www.ebay.com/itm/5PCS-RC522-Card-Read-Ante...All of them look like the board in my Instructable (except for the chip marking) and do not have the HW-126 you mentioned.

Yes, Miguel is the expert on these boards. I checked the link you provided and it looks like the Firmware Version is different on some of the clone boards (0x12 or 0x15 were mentioned). My boards are 0x92 (per the chip spec) and that's what my software looks for. Try one of the others mentioned in the link or just comment out the call to FW_Version in the Startup so it won't fail. Another thing I saw was someone mentioned communicating at 115k baud instead of 9600. Maybe try some other baud rates to see if anything pops up.

Does your non-working board look like the board in the picture above? I've purchased several of these and they all look the same so I'm not sure if someone is cloning the chips or not. there are other versions of modules that use this chip so they may be wired differently. If it looks the same try to see if there is any voltage at all on the EA pin. If it is a clone chip that pin may have something inside that is holding that pin at something other than zero volts. The only other alternative would be to try to solder a wire to EA and ground or touch EA with something like a grounded needle during power-up. It's supposed to read that pin at power-up so a temporary ground might tell you if it actually can go into UART mode. Good luck.

I just got three of these boards from a Chinese seller and two of them have the Uno bootloader like you state in your Instructable but one has the LilyPad bootloader. The only difference in the boards is that the "genuine" one says "LilyPad Arduino" instead of just "LilyPad". Also, some of the FTDI converters have the pins reversed so always look for "GND" (ground) to know which order to connect them.

You can just solder a standard ceramic capacitor to the unpopulated solder pads shown in the top right of the board picture. I use a 22pf capacitor but a 47pf also works. I had to do this in order to get the module to work properly below 4.75 volts.