Canon BJ-100 bubble jet printer help

[NikonKidF3]

Hello! I am looking for a bit of help with a Canon BJ-100 ink jet
printer. I bought this dead from someone on the Internet. Opening it up,
I found the miniature fuse for the head positioner motor was blown. I
replaced this with one of the same rating. The printer sprang back to
life, but the head smacked against part of the paper handling mechanism
that had popped apart. I immediately powered the prnter off, and
reinstalled the part.

The printer works pretty well, but with small font sizes there is a
vertical alignment problem. When the top of the line of text is printed,
sometimes the bottom of the line will not line up exactly. It seems to be
off by 1-2 "pixels" when it is printing bidirectionally. This is the
printer's only problem. The line of text is otherwise absolutely fine:
the spacing between the dots on an individual print line is even, and the
head moves smoothly back and forth.

I cleaned the two metal rails that the head rides on and lubricated it
lightly. The head is positioned by a toothed belt which is tensioned by a
small spring loaded wheel at the left end of the printer. The belt is
driven by a stepper motor at the right end of the printer. The motor
appears to be solidly mounted.

Any suggestions would be appreciated!

Willis Chung