In the description, there is "repair", but also "build, modify". And even if we just consider "repair", you can "provide details and have some electronic knowledge to perform measurements, provide schematics etc." without being a "trained professional". For example, I don't consider myself a trained professional, but I know I could ask an acceptable repair question (once the repair guidelines are clarified, though... what a mess...).
However, this tag should probably be killed, indeed. It looks like a meta-tag (like "beginner" or "example", or something like that), and doesn't really add value to the classification. In particular, it wouldn't work if a question had only this tag alone.
So let's get rid of it, but not for the reason you mentioned.
Edit: Had a closer look at the questions. In most cases, diy doesn't add any information. In some cases, however, it highlights specific questions where OP wants to achieve, by themselves, manufacturing steps that are usually made in factory houses, or build their own component parts. Examples:
I think this may be interesting to keep this subset of questions appropriately identified by a specific tag (diy may be a bit too broad and unspecific, though... Maybe "homemade", with an appropriate tag description?).