I have just added a second Kiev-90 to my collection, and I have noticed that there appear to be two versions. Possibly the change happened after the gap in manufacturing (1985-1987). I guess that the ones that I will call 'Type 1' were manufactured between 1983 and 1985, and 'Type 2' between 1987 and 1990. Perhaps those of you with Kiev-90s could check to see if this hypothesis is correct.

In the photographs above, the earlier camera (1985), Type 1 is on the left and the Type 2 camera (1988), is on the right. On the type 1, the leatherette covering goes almost to the bottom of the camera. The Manual/Electronic switch is different, and the button for releasing the hood is further forward on the earlier model. Note, the film magazines also differ slightly.
David.