Channel switching button seems to be having poor contact/broken.

@miguelcg99664 Awesome! Love those Fender's Anyhow, you are in luck. The switch itself is still available at plenty of places. Your Fender Frontman 15r part number for that switch is 028091. Check places like this I've never dealt with that seller, so this is definitely not an endorsement just an example.

To get to it, may require a bit of work on your part. I'd use something like this guide Fender Frontman 15r Transformer Replacement to get to the circuit board. Mark all your wires and take plenty of pictures so you know what connects back to what. Pull the knobs of the front controllers. There should be some nuts holding the potentiates to the front cover. You will need to remove those as well. Remove the screws/nuts that hold the board to the chassis. Now, with the board free, you could simply desolder the old switch and replace it with a new one. I would also suggest you clean the board with some +95% isopropyl alcohol. Check the traces for corrosion or even minor damage.

If in doubt about anything, or if you are stuck anywhere, post s a couple of pictures with your question. That way we can see what you see and hopefully we get this amp back on the road. Aggiungere immagini ad una domanda

Just in case, here are Fender Frontman 15 Frontman 15r Schematics

While you work on your amp, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has a device with the same issues as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.

Repair is War on Entropy!