Epson LQ-870 Service Manual page 113

REV.-A
Table 5-5. Repair of in the Main/Drive Circuit Board (Continued.)
Problem Symptom
Self-test print- Self-test is
ing is not executed.
abnormal.
A particular
dot is not be-
ing printed.
Paper is not
The paper
fed normally. does not
feed, or the
feed pitch is
abnormal.
Printing of da- Data corrup-
ta from the
tion occurs
host comput- when the par-
er is faulty.
is used.
Cause
Measure the voltage at Vref (pin 1) of
The CPU can't
measure the
voltage on
the +35V
line.
At IC4B, check the input signal at pin 10 1
and the output signal at pin.
defective.
IC28 is defec-
tive. IC8-IC 13
are defective
defective.
defective.
5-18
Checkpoint Solution
Replace IC4D.
Replace
Replace IC20.
Replace IC6A
or IC4B.