Welcome to the forum.
I've not had one of these units for repair, but have worked on quite a few pedal switchers and here are some checks that I carry out;
1. Does the display brightness modulate with the sound?
2. Make sure the unit is powered off the same mains socket/extension as the amp.
3. Don't run the unit on top of, or in close proximity to the amp. Magnetic fields can interfere with the switcher's electronics.
4. If possible, factory-default the unit to 'out of the box' programming.
5. If the unit has switchable buffers, turn these off and compare with them turned on. Any difference?
6. I test the signal path by looping every send/return with a patch cable and activating them all in 'live' mode (or whatever your manual calls it when you can use it as a simple stompbox array rather than pre-programmed loops) The unit should pass a clean signal if they're all on, or in any combination.
I don't know about your switcher, but many/most use relays to route the signal. You can sometimes hear the relays click if you hold your ear to it and switch. If yours is like this then the active electronics serve to operate the relays and the buffers, but have no other bearing on the signal. If there's an internal power supply problem I would expect either the control electronics to give erratic switching, or for the buffers to be affected. Equally, an internal fault could give rise to buffer problems and there's an unknown with those buffers - the signal through them could be controlled through semiconductors rather than relays. If by relays, then your entire signal path is 'hard-switched' and I can't easily see why the signal would be affected.
Then again, I have no knowledge of your unit and the signals could be routed purely electronically, rather than by elecro-mechanical relays.