Epson LQ-2550 Technical Manual page 228

I
WARN ING WAR NUN13 ATTENTION
Hot
(a) Back of the printhead
Table 5-6. Relationship between Common Wires
and Each Coil
F
Common Corresponding Common Corresponding
Line Coil Numbers
c l 1, 9, 17
5, 13, 21
C2
C3 12, 20, 24
C4 4, 8, 16
If a specific dot is not printed, one possible cause is a defective printhead coil (refer to Figure 1-2 for
the relationships between the coil numbers and wire pins).
Whether the coil is defective or not is determined by measuring the resistance across the terminals
of the common line and corresponding coils (refer to Figure 5-5 and Table 5-6). The normal resistance
for a printhead coil is 8.6 !2 + 10% (at 25"C).
If a thermistor, a temperature sensor in the printhead, is shorted, the message "HEAD HOT" is displayed
on the LCD even when printing is not being executed. The relationship between the printhead
temperature and thermistor resistance value in the normal state is shown in Figure 5-6.
Figure 5-5. Printhead Connectors F and R Wiring
R
Line Coil Numbers
C5 2, 7, 15
C6
3, 11, 19
C7 14, 22, 23
C8 6, 10, 18
I
5 I 1321 9 17 C
I C2C3C4Z420
D
3 II 192
C 5 C 6 7 c7
(b)
25
Figure 5.6, Relationship Between Printhead
Temperature and Thermistor Resistance
5-16
F
1 5 2 2 2 3 1 8 1 0
I
I
I
I
I
I
– r - - - - - - -
I
4.3 5 0
Thermistor Resistance Value