Test Points On The Main Circuit Board Unit - Epson TM-U675 Service Manual

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Test Points on the Main Circuit Board Unit

After a main circuit board unit failure, one basic method for diagnosing the cause of the problem
on the main circuit board unit is to check the power supply line. Use the following table to check
the power supply line. First, check step number 1, and proceed to the next step if that is not the
problem.
Table1-4 Checking the power supply line
Step
# Type of Voltage
1 Voltage input
from the power
supply
2 Voltage input
from the power
supply
3 Logic voltage
(VCC)
4 Logic voltage
(VCC-PWR)
5 Logic voltage
(VCC-PWR2)
6 Logic voltage
(VCC_SEN)
1-12 Troubleshooting
Location of Condition of
Measurement Measurement
CN29, pin 1 Output when
the power
supply is ON.
U11, pin 1 Output when
the power
supply is ON.
VCC pad Output when
(near L2) the power
supply is ON.
VCC-PWR pad Output when
(near U14, Q51 (C) is "0."
pin 40) (24V SW1="H")
U19, pin 8 Output when
potential Q60 (C) is "0."
(24V SW2="H")
CN30, pin 5 Output only
potential when there is
output sensor
conductivity
when CPU
output port
(SEN_PWR) is "L."
Normal
Value Presumed Cause of the Error
24 V ± 10 % It is possible that the problem is pre-
arcing of the F1 fuse. The fuse may
have pre-arced because of an
unusual input circuit.
Always replace the fuse after
removing the cause of the pre-arcing.
If you do not remove the cause of the
pre-arcing, and replace this fuse, the
problem may expand to
misoperation. Also, always use the
specified type of fuse when replacing.
24 V ± 10 % It is possible that the problem is pre-
arcing of the R3 fuse. The fuse may
have pre-arced because of a
problem in the logic power supply
circuit or because of a VCC over-
voltage.
If pre-arcing of the R3 fuse happens,
do not repair the main circuit board
unit. The quality of several parts on the
circuit board is weakened by pre-
arcing of the R3 fuse and safe
operation cannot be guaranteed.
5 V ± 5 %
It is possible that the logic power
supply circuit has malfunctioned.
If you find this line has a problem, do
not repair the main circuit board unit.
The quality of several parts on the
circuit board is weakened, and safe
operation cannot be guaranteed.
5 V ± 5 %
The logic power supply circuit or Q44
could have malfunctioned.
5 V ± 5 %
The logic power supply circuit or Q59
could have malfunctioned.
5 V ± 5 %
The logic power supply circuit or Q44
could have malfunctioned.
Rev.D