[Toymeister]

I would start with the basic trouble shooting. Normally I would try direct 220 to each heating element, if that works check any safety switch (door). You have already done that, what you have If is a bad motherboard (control board). It is overheating. It is a remove and replace job. If you want to diagnose it at the component level and are not into the schematics, check for capacitors that are split (burst open) on the control board, usually those fail first.

The control boards are made under contract in China. Smaller capacitors and smaller heat sinks are used to save costs. The same sort of failure is common in LCD TVs as well.