Has anyone ever gotten Meraki MX-60(W) JTAG to work?

I accidentally erased my NAND when trying to install openwrt on a second-hand MX-60W. After reading around, it seems like the only recovery path is a JTAG install, and the MX-60W does have an (unpopulated) JTAG header on its board. Since I have a RaspPi capable of running OpenOCD, I thought I'd give it a shot.

After a bunch of configuring (and soldering) however, I'm about to give up. OpenOCD reports all zeros on TDO, even when it and TCK are the only pins connected. I tried a number of different TCK values (1 kHz - 1000 kHz) with the same result.

Has anyone ever gotten JTAG working on these devices?