Service manual

Troubleshooting
EPSON FX-880/FX-1180 Service Manual
5-5
Printhead Driver
If the printhead is not working but its solenoids test okay, check the driver circuitry. Also, check the driver
whenever you find a defective solenoid in the printhead. (When a solenoid goes out, it sometimes
damages the driver.) When testing, you should make sure that all transistors within any group in the table
below have readings consistent with each other, within ±10%. The printhead may be left connected during
this procedure, but the printer itself must be unplugged from the power supply.
Table 5-7. Printhead Driver Test Points
Transistor Leads to Measure Across Meter Reading (resistance)
B
→
E
Neither open nor shorted.
E
→
B
Neither open nor shorted.
B
→
C
Neither open nor shorted.
Power Transistors (for
individual dot wire
solenoids)
Q2,Q3,Q4,Q5,Q6,Q7,Q8,
Q9,Q10
C
→
B
O.L.
B
→
E
Neither open nor shorted.
E
→
B
Neither open nor shorted.
B
→
C
Neither open nor shorted.
Power Transistors (for
common leads on
printhead)
Q21,Q22,Q23,Q24,Q25
C
→
B
Neither open nor shorted.
B
→
E
Neither open nor shorted.
E
→
B
Neither open nor shorted.
B
→
C
Neither open nor shorted.
Small-signal Transistors
(surface-mount type)
Q11,Q12,Q13,Q14,Q15
C
→
B
Neither open nor shorted.
B
→
E
O.L.
E
→
B
Neither open nor shorted.
B
→
C
O.L.
Small-signal Transistors
(surface-mount type)
Q16,Q17,Q18,Q19,Q20
C
→
B
Neither open nor shorted.
Note: The middle lead on the surface-mounted transistors corresponds to the base.