Samsung induction range not holding oven temperature

I have the NE58H9970WS samsung induction range. Bought March 2016. Oven hasn't worked properly since we bought it. Preheats fine to lets say 425. You then put food in it and temp drops to 350 because door was opened. It quickly regains to about 378 and then just starts dropping again all the way to 350 and after one hour, it has only come back up to 358. We've already replaced the main control board, the sensor and the lower heating element but the problem remains. I can hear the clicking telling the heating element to come on and then it seems to click again right away to turn it back off. The heating element does come on but only for a moment and then gets turned off again. Service technicians can't figure it out.
This does not appear to be a problem at lower temperatures of let's say 325 or 350.
Any help or ideas would be appreciated. Also, where could I get a service manual for this model?

via Samsung induction range not holding oven temperature
by paaschjc