2013 Fender Champion 100 power issue

[Psabin8951]

I have a Fender Champion 100 which sounds great some the time but randomly stops powering on properly and just blinks the power LED. Next day it is likely to work.
Everything I go to look at it it works fine. Tapping the PCBs in various places makes no difference. No obvious bad solder joints.
Any pointers please?

[g1]

I would guess some cap(s) not up to par in the smps unit.
I only have schematic for Rev.A (attached).