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Here is the wiring diagram
http://manuals.frigidaire.com/p...assomption/318271958.pdf

Here is a sheet I found on error codes.
http://frigidaireservicetips.co...aultCodesandRTDchart.pdf

Can there be a short in the oven light circuit?
I doubt it would be a short as this should blow the breaker.
More likely an open with something else contributing to the problem.
Could be you are feeding bach through earth grond instead of Neutral.

You are somehow supplying Neutral or power to the control board through the fan switch and/or the stove top elements.

I would check the power to the unit just so it can be eliminated as a possible cause. Do not understand why the service tech did not do this.
L1 to L2 should be 240 volts odds are high this is OK as the stove top elements work.
L1 to Neutral and L2 to Neutral, both should be 120 volts.
Check with and without the unit connected.

If this is a 3 wire hook up I would check that the ground strap from Neutral to the units frame is OK. Also check all connections at the units terminal strip.

If the above is OK disconnect the light switch, to see if it now operates correctly.
If no change
Disconnect the temperature probe. F30 is a temp probe error so could be it is doing something weird like shorting to the frame internally.
Note with it disconnected you will not get any heat as the unit will think that it is over temperature.

Just a couple questions.

Did this unit work here in the past?
Has anything been done recently with the wiring to this unit?
Is this a 3 wire or 4 wire connection?
What are the voltages at the terminal strip when the panel is working?

Something is very, very strange.
You should not be able to measure 240 volts when referenced to Neutral or ground. It can only be between L1 to L2.

Do not know how much you know about electricity but here s how it works.
Note the explanation is not strictly true but will do to explain this.
You have two 120 volt AC lines coming into the house and they share a common Neutral and they are 180 degrees out of phase.
So when one is at positive 120 volts, the other is at negative 120 volts when referenced to the common Neutral.
When referenced to each other then you have 240 volts.

So I would have to say that it sounds like the stove/line cord is wired up incorrectly as that is the only way I can think of for you to measure 240 volts from the center connector on the strip (Neutral) to either of the other terminals.

I would remove the cord from the unit and check it with a meter.