Rudy horked up an altimeter for me in the late 90's but maybe better now. There is a shop in Hot Springs, KHOT, that I have been very pleased with SAS Instruments. The guys name is Earl.
Find out what brand it is. A lot of shops will say yes, you send it to them, they get it, then tell you they don't work on that brand and offer to sell you a new one. Ask them if they work on THAT BRAND SPECIFICALLY.