Microwave cooktop light stuck ON

The cooktop light bulb burned out and I replaced it and now the light stays on all the time - the panel button (ON/NIGHT/OFF) does not seem to work anymore. We leave the light on NIGHT every night and now it just stays on the entire time. All the other buttons on the panel pad work fine. Any ideas what it will cost to repair.

I think this is Model and Serial number (not sure which is which)

MH6150XMB-0
FGM3407049

Most likely the problem is a bad control board. Unfortunately this part is no longer available.

Here are the break down diagrams for the Whirlpool microwave http://www.appliancepartspros.com/partsearch/model.aspx?diagram_id=125320&&model_id=503331

Gene.

Gene.