Why microwave doesn't turn off?

My GE microwave is like 19 yo. However, it always worked well, until now. I keep it clean and use covers to avoid spill food. It doesn’t stop working after time is over, nor when door is open. It still works, it just not stop working.

I love this microwave and its size. It is hard to find the same size for a good price and it is hard to replace it. I like to have it over a counter or table at a high that is safer.

I don’t like the one is over the stove where it gets hot when cooking, specially with a gas stove. I have to reach over the stove flames or steaming pots and get too close to stove, even when I use only median heat. And being a short person. When microwave is in high level it is a risk to spill something hot over myself . For now, I have to use a step, but I still could have an accident going up or down over the step stool and near the stove. I wish it can be fix. The other model that convinced me and I ordered to replace came damaged, and store was sold out. No have much time to keep looking, I prefer this can be fix to reuse it or recycle like donate to someone who could fix it, not make more junk trash.