The Grundig Satellit 800, if I remember right, has some similarities in the schematics with Drake receivers like the SW8. I think any ham radio repair shop should be able to repair it if it is repairable. Look at fuses inside if there are any. Most likely there is one or two voltage regulators after the power cord/ battery compartment. I would check dc voltages there and at the output of the regulator. Also very trivially the power button could not make a good contact. Check the obvious first. Check for leakage in the electrolytics (deformation of the top of the electrolytics or leakage from the bottom) even at the audio stage (just at the output of the RCA sockets). If they leak and short, It might not allow to power it. In that case a bad fishy smell could be apparent.