Could you advise the model of Sanyo, this sounds like a main board or power modulator fault where the capacitors are taking longer than normal to charge. Once I have the model number I will have a better idea.
This appears to be a hardware fault relating to the main board.
Unfortunately you are going to need to get the main board replaced, it is fixable but not something I can talk you through yourself.
Its likely the fault will get progressively worse until one day it will not power on at all, however by leaving the unit with a fault there is also a chance it may cause damage to other components, as its not regulating the power properly.
If you provide me you postcode I can give you details for a suitable TV repair service in your area
I have referred other customers to H AND H ELECTRONICS and heard good things about their service, they are within a 3 mile radius of the postcode.
If you drop the TV off to them, they will inspect the TV and if you chose not to use them to repair it after they give you a quote you can walk away (no obligation to use them for repair).
If its the power board its likely to cost around £40-50, and would think this is a worthwhile repair.
Their address is: 290-292 Preston Rd, Harrow, Middx HA3 0QA