It's quite possible that negative pressure is created. When you switch to a soffit/ridge vent setup, natural airflow takes over. There's no mechanically forced air, obviously, in the latter setup.
As always, have the ridge vent run peak-to-peak, no closer than 3' from the peak. Make sure your soffits and the 'chutes' between the rafters are free from insulation and/or obstructions (like boxes and hanging clothes.) You want the air to rise, unimpeded, up through the soffits and along the roofline and out the ridge vent at all times. Then, turn the fan off. WHen you strip the roof and re-shingle, replace the sheathing that had the turbine in it.
The best scenario is for the soffit vents to run full length of the soffit. This will help equalize any pressure issues and possibly prevent a wind-driven rain or snow from entering the attic through the ridge vent. The deeper the baffles on the ridge vent, the less likely you'll have this problem.