GR & HGR Do Not Work

["Bryan Parkoff" <BParkoff@satx.rr.com>]

GR & HGR Do Not Work

    It does not work on Apple II+.  I tried to type GR or HGR, but "@" was
filled from top upper-lef to the bottom down-right.  I mean that it will
show only text, but no graphics.  Do you have ideas that it may have
something wrong with the type of chip in the motherboard.  Where can I find
Apple II hardware (Not Apple II Reference) book and/or Understanding Apple
II book?
    I should be able to repair motherboard myself without sending it to the
repair deptartment.  It is very hard to find where repair department
locatio.  Thanks a lot!!!

Bryan Parkoff
BParkoff@satx.rr.com