The heads are selected by U4 (75451 dual AND gate/driver),
the outputs of
which are pulled to+5V, and slo drive the bases of Q7 (Head 1) and Q6
(Head 0), PN2222 transistors via restors. One input of each
of the AND
gates comes from the power-OK circuit, built round Q9 and Q10
(as this is
common to both heads, it's working correctly), the other
input comes from
the sides select signal on the connector (U4b, for head 1) or
from that
signal inverted by U8b (7414) on U4a, for head 0. That should
give you
some components to check.
Are you sure U4a drives Q6 and U4b drives Q7? Tracing the board shows them
on Q7 and Q8. Yikes. Any chance you could scan the schematic and email it?
No, I misread it. It's Q7 and Q8 as you said. Q6 is the erase driver.
1bpp tiff, bmp or pcx would do. The higher the
resoultion the better, but I
could probably make due at 150dpi.
Alas I have no scanner, and nothing to connect it to :-(
-tony