Light Up; Needle Bar Is Raised And Feed Pulse Motor When Needle Bar Is Lowered); Pattern Cannot Be Selected; Main Motor Does Not Run - Baby Lock BL7800 Service Manual

∗ You must turn off the power and remove the connectors from printed circuit boards before measuring resistance.
∗ Refer to the illustrations for check locations.
PROBLEM
When power is
1.
turned on, buzzer
does not sound and
the LED does not

light up.

After the power is
2.
turned on, pulse
motors do not
return to their home
positions with
respect to the
needle position.
(Zigzag pulse motor
when needle bar is
raised and feed
pulse motor when
needle bar is
lowered.)
Pattern cannot be
3.
selected.
Main motor does
4.
not run.
CHECK
If the voltage between both inlet terminals is
1)
measured when the power cord is plugged in
is the standard voltage (120 VAC, 220V,
230V, 240V) displayed.
When power switch is set to on, is resistance
2)
at both ends less than 1
Remove connector CN2 from the power
3)
supply board, and check following voltages
using a tester:
Voltage between pins 2 and 3 should be
about DC 5V. Voltage between pins 4 and 5
should be DC 20 to 30 V.
Is the fuse blown?
4)
Other
5)
Are the resistances between the connector
1)
pins given below normal for pulse motors
which do not return to the home position?
(CN1).................. 1-3, 2-4 → 8 to 10 Ω
Zigzag
(CN2).................. 1-3, 2-4 → 8 to 10 Ω
Feed
Set the home position for the same pulse
2)
motors irrespective of needle position.
Is a fuse blown?
3)
Is the voltage between pins 4-5 normal when
4)
the connector (CN9) which is output from the
power supply board is disconnected?
Between 4-5 DC 20 - 30 V
Others
5)
Does switch on SS PC board remain in the
1)
pressed condition after the key on the
operation board is pressed?
When the foot controller is connected, does it
2)
remain depressed?
Others
3)
Does the balance wheel rotate easily?
1)
Is main motor connector (CN2 on power
2)
supply unit) connected properly?
Is resistance of both ends of main motor
3)
connector (CN2 on power supply unit) 24 to
Ω
34 ?
Do start/stop switch, backstitch switch, needle
4)
position switch, and thread cutter switch
operate correctly?
Resistance at both ends of each switch:
When switch is pressed .......... 1
When switch is released
Ω
?
Ω .
or less
......... ∞
- 38 -
REMEDY
Replace the power cord.
1)
Replace the power supply unit
2)
assembly.
Replace the power supply unit
3)
assembly.
Replace the fuse after correcting
4)
defect that caused fuse to blow.
Replace the main PC board
5)
assembly or operation board
assembly.
Replace the pulse motor which
1)
shows an abnormality, or the
lead wire assembly.
Replace the NP PC board
2)
assembly.
Replace the fuse after correcting
3)
the defect that caused the fuse
to blow.
Replace the power supply unit
4)
assembly.
Replace the main PC board
5)
assembly.
Adjust installation, or replace the
1)
SS PC board assembly or
operation board.
Check.
2)
Replace the operation board
3)
assembly or main PC board
assembly.
Adjust the installation position so
1)
that it moves easily.
Check
2)
Replace the main motor.
3)
Replace the SS PC assembly.
4)