I live here and have a work permit. You do not need a work permit for machine repair, thats a specialist task exempt from a work permit. My work permit is to perform and manage installation activities and even to train others, for this I have a work permit and can extend if if I wish for the whole year or longer so it is not short term. If there are on going projects with no local skilled persons t perform the tasks you can do longer than one year.
There are couple of things, you can work in Thailand for up to 15 days without a permit, for such things as fixing machines, also can use visa exempt for business meetings conferences etc but not actually work. To get WP obviously need a visa I have Non o based on marriage my friends all got Non b, some whlle here some from home country. We had to get invite letter from a distributor to support WP application. It is allowed for skillsets not available within Thailand.
You can get a work permit on non o visa based on marriage from outside thailand or extension based on marriage obtained in Thailand. Currently I have 12 months non o based on marriage from savannakhet and have a work permit.