My turbo chef owen sense somtime 208vac and some time 240vac

Hello. If you take the right side panel off, unplug first please. at the back is a blower motor, two screws on the back vertical rail, and one at the front edge of where it is connected to blow, probably under the foil tape, this will remove the blower. On the back wall toward the bottom, under all the relays, is a voltage transformer that tells the controller which voltage you have, replace it, and problem will be corrected. If you are not comfortable with this, call Turbo Chef for a local servicer, and call them to repair.
As for the F6 EC error, you are having a temperature problem due to the control area overheating, there is a blower on the back, and vents on the front, and side, either these are clogged, the fan grid is clogged, and the interior has alot of dust coating the interior of the right side, please unplug, vacuum, and clean out the dust etc.., after reassembly, after about 30 minutes of operation, the blower on the back should be on, if not you need another.

Hope that helps, and thank you.