try first if you use the mg7550 boot but the console should be closed anyway ... even if you do the short SO pin, in the worst case this will only leave the mac addesses in emergency mode type xx: xx: de: ad: xx: xx and by oid snmp you can activate the serial console, I disregard the oid in broadcom that activates it .... over the noisy boot is only to stop the system boot and allows you to write in the sectors or groups of the flash. Try to make the short at just the moment the system loads the console should be unlocked in most cases always like this or it will allow you to put the modem in the factory and send the corresponding oid to have a serial console!
P.S
sorry my english, I use Google translator ... my native language is Spanish I hope it is understood
P.S
sorry my english, I use Google translator ... my native language is Spanish I hope it is understood