How do you know it is "locked"? Perhaps that is the only frequencies used where you are located.
The HX850S can be purchased for about $240 US dollars. With repair rates at about $75/hour, it might be a good time to purchase
a new 850 with all the channels.
All marine VHF radios sold over the last 15-20 years come with a switch or button that says "INT/USA" International frequencies have some variations from the USA frequencies. Those differences are on only a very few channels. When outside the USA use the INT. When in USA waters use the USA side of the switch.
Camper Nicholson 35