Some large A&P shops will have one guy who is certified to work on
avionics ("instrument repair" according to RST). However, most shops
use roving instrument guys who come by once or so a week. The
certification necessary to work on avionics is different than the A&P
certification.

I have run into this with aircraft owner's that are working on their
private tickets. Most don't realize that they need to have a
transponder inspection every 24 months for VFR flying. An A&P cannot
perform this test and most IA's don't mention this at annual because
they don't consider it their business.

-Robert