I have an RB 750 router that has a broken/missing reset button. When I opened up the case I noticed there is a set of jumper pins. Is this a reset jumper? Can this be used to get into netinstall mode? Currently the router is in a reboot loop after a failed upgrade and I need to find some way to recover it. 
check here:
http://routerboard.com/RB750
or get some schema from there and show where are these jumpers, i cannot find one on my sample on the table.
I should have mentioned it is an Rb750Gā¦
Those jumper pins are for powering a fan.
You should try to reset with jumper hole to see if it stops reboot loop, but in the end reset button is the only way to make RB750G look for Netinstall.