Epson LQ-870 Service Manual page 111

REV.-A
5.4 REPAIR OF THE MAIN/DRIVE BOARD
This section provides instructions for repairing the main board when it is defective and describes various
symptoms, likely causes, and checkpoints. Checkpoints refer to proper waveforms, resistance values,
and other values to be checked to evaluate the operation of any component that might be @ad. Check
these values and take the appropriate action.
Symptom
Problem
he printer The CPU does
not operate.
does not op-
rate at all.
Table 5-5. Repair of in the Main/DRIVE Circuit Board
Cause
The reset cir-
operational.
Selection of
control ROM
is abnormal.
Checkpoint
Check the voltage waveforms for the + 5V
line (IC5C pin 7) and for the THLD signal
Check the voltage waveforms for the
THLD signal (IC4B pin 10) and for the
RESET signal (IC4B pin 12) when power
is on.
Check pin 2 1 of IC 1C for the Vxvoltage
(NMI signal HIGH).
Check pin 71 of IC4B for a change in the
signal HIGH/LOW.
5-16
Solution
Replace lC4B.
Replace IC4B.
Replace IC2C.
Replace IC4B.