Hi,

If the Roku’s motherboard has been affected by a power surge, it will be easier to get a replacement device than to try and fix it, as doing this without a schematic diagram or service manual will be extremely difficult.

You could try finding a replacement motherboard to see if that is any cheaper. I searched online without success. You may have better luck

If you do manage to find one, here’s a link to the ifixit Roku 4 Motherboard Replacement guide which may be of some help.

If you live in an area prone to power instability or to storms, as a suggestion for the future, connect the Roku via a surge protector or a powerboard that has inbuilt surge protection and where the manufacturer also provides cover for equipment damaged by electrical surges if connected via their product.

This is just an example and the fine print of what I mean.

There may be makers of surge protectors/powerboards where you are that provide the same.