EX3700 Restore OEM Firmware from OpenWrt

Hiya! For various and sundry reasons (including problems with 5GHz), I'd like to put the factory firmware (a .CHK file) back on my EX3700 wifi extender.

The typical "press button while booting, tftp file over" method common to Netgear routers doesn't work (looks like it goes into OpenWRT failsafe rather than Netgear super-secret-squirrel mode and there's no tftpd listening looks like).

So either:

  1. Is there a way to use mtd or sysupgrade to put stock firmware back on (maybe a breakdown of the chk file format), or
  2. Is there a way to trigger the Netgear fallback mode on this device?

TIA!

Have you tried going into the LuCI interface, going to System > Backup/Flash Firmware > Actions > Flash new firmware image, (uncheck "Keep settings") and just pointing to the factory .CHK file? This has always worked for me in the past on Netgear equipment when I want to go back to OEM firmware.

(P.S.: I believe this method assumes that the device doesn't use NAND flash storage.)