I find turntables & cassette machines a giant pain in the butt to fix. There's no fast way to do a good job, and customers mostly pin their expectations about repair price to the cost of acquisition - LOW.
Some of those coffin size hi fi cabs have tube amps, mostly lowest quality possible. And the actual fidelity of the built in speakers is well, not much for fidelity. Did I mention they are a giant PIA to move around?
If you have the patience to deal with the gear, all power to you. Charge accordingly, and let your customers know in advance they're not going to be charged 1970's labor and parts prices. I keep a turntable and a cassette deck for myself, and point customers to other facilities that deal with them so I can concentrate on the work at hand, and not further clog my shop space with fragile turntables, enormous wooden boxes and tape machines of dubious quality.