Interessting - not funny. I have nearly the same Problem ... excatcly that above shown part seems to be defect. turning on the Printer, the heatbed starts heating - and it smells bad to. i turned off power, when the heatbed temp. runs above 120°C ... and it did it really fast. I found, that the chip was about 138°C ...
Contacting the ultimaker Support the send me to the german Reseller - after discussing a week!!! with them, they decided, that i am right (at first, the wanted to sell an new heatbead) ... a new heaterboard should be about 120.- EUR without Transport ... that heavy.
asking aunt Google, i found someone else with exactly the same problem. they told - that the chip is an TI CSD18501 or CSD18501Q5A ... how can i get the Information, which chip and where to by? or an alternative new heatercontroller