my dryer drys fine but does not turn off
Here are your parts
http://www.appliancepartspros.com/partsearch/modelsearch.aspx?model=fde700fhso
Here is the wiring diagram
http://manuals.frigidaire.com/prodinfo_pdf/Webster/131826200.pdf
Have you checked/cleaned your moisture sensor (Item 8 in Section 2).
The below is if the timer is not advancing in auto modes.
This is two metal strips with a space between them. When clothes are wet there is moisture between the strips and this passes a small electrical current.
The board monitors this and holds the timer off. When the clothes are dry there is no moisture so the current stops flowing and the board then advances the timer.
Any dirt etc. between the strips will make the unit think the clothes are still wet and not advance the timer. Clean between the strips with a damp cloth, drying thoroughly . If this does nothing try cleaning with isopropyl alcohol or electronics cleaner, just make sure that all the vapors have dissipated before trying it.