https://www.ifixit.com/Answers/Device/Fender_Frontman_15r
Fender Frontman 15r Repair Forum - iFixit
Fender Frontman 15r questions - have frontman 15g.is power switch my problem? - I have a broke 1/4 inch input jack - Channel switching button seems to be...
fender frontman 15rrepair forumifixit
https://www.ifixit.com/Answers/View/153081/have+frontman+15g.is+power+switch+my+problem
SOLVED: have frontman 15g.is power switch my problem? - Fender Frontman 15r - iFixit
Its MOST likely a loose solder connection somewhere in the unit, maybe on the front panel jack, maybe on the volume pot. It could also be the output IC...
power switch