First of all, that senior told you the truth, medical equipment maintenance, in hospitals are mostly equipment department, medical engineering department and so on. Belong to the auxiliary departments, for clinical services. But high grade hospitals, income is still good. 4-5000 are not surprising, in coastal cities can be 7-8000, or even higher.
Second, you said the promotion and certification issues, university graduates into the hospital is an assistant engineer, belonging to the primary title, five years after the engineer can be examined belonging to the intermediate title, and then after the examination of the senior engineer, belonging to the senior title. The higher the level, the higher the income. Do any work, as long as you have the heart to do a good job, promotion opportunities are for the best people. The ones who muddle through every day are the same everywhere. If you can drill in, get a certain type of instrumentation refined, understand, become an expert (at least in your hospital is, this goal is not difficult to achieve), then it is different, you will be very proud.
Lastly, the hospital is a public institution, the same type of work for a long time will make people feel a little boring, but then again, where the work is not boring.
I hope you will take advantage of the opportunity and consider it carefully.