Readynas NV+ v1 needs TFTP

My NV+ has been playing up.  Have resolved PSU issues, but this has left the NAND in the unit corrupted.  When I turn on I get LEDs 1, 2 & 4, which points to NAND corruption.

Then regardless of what reset steps I follow, I end up at LEDs 2 and 4, which I think indicates an attempted TFTP boot.

I cannot get the unit to do a USB recovery.

I cannot find any instructions on how to execute a TFTP boot.  I also don't know what files need to be presented.

I've created a simple TFTP server, and connected my laptop to the Readynas, setting 192.168.125.1 as my laptop IP address.  I see no 'activity' in the TFTPD64 window.

Can anyone help me with TFTP files and instructions for NV+ v1?  thanks