Like the compact AP150 (pictured below), the Canon AP400 suffers from yellowing plastic syndrome.
Great keyboard, but not an especially attractive typewriter, and too bulky to collect unless you happen to own a large warehouse.
The typing action is more sluggish than on the compact AP150, which is not surprising since the print unit has to carry a larger ribbon …
It works fine except that the right margin buzzer doesn’t work, which is a serious problem because by the time you realise you need to hit the Margin Release button it’s too late and you’ve lost track of where you were (writing-flow interrupted).
Still, it was nice to get briefly acquainted with this old dinosaur (1984/85 probably, based on a quick reference “Guidebook” which has a reference number suggestive of April 1984).
The Guidebook can be stowed away inside a plastic pocket under the front lip of the machine …
Canon AP400 Guidebook: