Epson Stylus COLOR 900 Service Manual page 88

EPSON Stylus COLOR 900/900N
Table 3-32. Cleaning Does Not Solve the Print Problem (continued)
Step Problem
8 Is a head driver Locate the following four power transistors attached to
transistor defective? the heatsink on the main board:
• Q3 and Q4: Output the common voltage for rows
A and B (black nozzle rows).
• Q5 and Q6: Output the common voltage for rows
C, D, and E (color nozzles).
To check if each pair of transistors is working
properly, check the trapezoidal waveform at the
emitter terminal of the charging transistor (Q3 and
Q5). Perform the check while printing.
NOTE: The frequency and amplitude of the
Solution
H e a t S i n k
T H
Q 3 Q 6
Q 4 Q 5
B 1 3 8 2 D 2 0 8 2 B 1 3 8 2 D 2 0 8 2
B E
2 0 V 2 µ
waveform vary while printing. As long as the
trapezoidal waveform is output, the head
driver transistors are considered good.
Table 3-33. Cleaning Does Not Solve the Print Problem (continued)
Step Problem
9 Is the printhead pre- Check for the waveform at the base of transistors
driver IC defective? Q3 - Q6 as shown below.
If the waveform is not output correctly from Q3 or
Q4, replace IC15 on the main board; if it's not
output correctly from Q5 or Q6, replace IC16. If the
waveform is output correctly, replace the
corresponding power transistor.
Chapter 3 Troubleshooting
Solution
H e a t S i n k
T H
Q 3
Q 4 Q 6 Q 5
B 1 3 8 2 D 2 0 8 2 B 1 3 8 2 D 2 0 8 2
B
2 µ
2 0 V
E
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