Laserjet 400 m451dn ethernet lost network connection

I have a Laserjet 400 m451dn that has been working perfectly since I set it up 3 months ago, connected via tplink powerline ethernet adapters. Then one day the wife said the printer is off line, I restarted everything and it seemed to resolve the issue but then it went off line a few days later.

Now after multiple restarts, plugging the printer directly into the router, factory restored settings, manually configured IP address, reset again back to dhcp, changed ethernet cables, tried an ethernet switch between the router and printer, nothing is working. The lights are on when the ethernet cable is plugged in and the router says 100 Mbps connected but the printer does not obtain a valid ip address and does not show up. If I set a manual ip address I can't ping it on the network. I'm guessing a hardware fault, maybe a failed network card in the printer but just not sure if there is anything left to try before admitting the printer is toast.

Any help much appreciated.