Hi this is one that really needs to be checked. If it was kept out of the elements as best possible. There is a good chance it can be fixed and for not much.
Usually what causes this to happen is dried out electrolytic capacitors and they cost only a few bucks each. You will need a few of them of different values.
But you can take the head unit to a marine shop local to you for this repair, mos will send it out and have this done. If you have a West Marine you can check with them on this;-)
Please rate kindly at this time, I will then be able to remain with you in case you need further information.
Thank you and have a wonderful day! Tech Michael