Yesterday, when I was using a printer, it suddenly turned off in the middle of printing. I was surprised and pushed the power button many times, but it never turned on again. I realized that it had broken down. I have used it for about four years.
Is this use of the Present Perfect following the Past Perfect okay, since the author has used the printer for quite a long time? That is, using this Present Perfect, the author is shifting the passage from "me yesterday" to "me today".
Or should one necessariliy backshift it to
I had used it for about four years.
Alternatively, can one use the Present Perfect in both sentences:
I realized that it has broken down. I have used it for about four years.
..since the event is a recent one (yesterday) and the condition still obtains (the printer still exists and it is in a broken-down condition).