Brother LH4-B800E Service Manual page 165

6. ELECTRIC MECHANISM
Code
<Software>
1. If the sewing machine stops before the needle up position, reduce the setting value for machine
motor parameter No. 00 (machine motor stopping position).
2. If the sewing machine stops after the needle up position, increase the setting value for machine
motor parameter No. 00 (machine motor stopping position).
<Hardware>
1. Turn the machine pulley by hand and check if the upper shaft locks or not.
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(If it locks, remove the cause of the problem.)
2. Check if connector P3 on the main circuit board is securely inserted and if any harness is
broken or short-circuited.
3. Check if the machine motor harnesses are securely inserted and if any harness is broken or
short-circuited.
4. Replace the synchronizer.
5. If there is still an error even after replacing the synchronizer, replace the main circuit board.
1. Turn the machine pulley by hand and check if the upper shaft locks or not.
2. Check if connector P3 on the main circuit board is securely inserted and if any harness is
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broken or short-circuited.
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3. Replace the synchronizer.
4. If there is still an error even after replacing the synchronizer, replace the main circuit board.
E-74 1. Replace the main circuit board.
E-75 1. Replace the main circuit board.
1. Make sure that ROM chips of the main circuit board are correctly inserted. (Check position,
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orientation, lead clinching.)
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2. Replace the main circuit board.
1. Turn the machine pulley by hand and check if the upper shaft locks or not.
2. Check if connectors P3 and P6 on the main circuit board are securely inserted and if any
harness is broken or short-circuited.
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3. Check if machine motor harness connector CN7 and power supply harness connector CN8 on
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the 1-step power supply circuit board are securely inserted and if any harness is broken or
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short-circuited.
4. Replace the 1-step power supply circuit board.
5. Replace the main circuit board.
1. Check fuse F1 on the main circuit board.
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2. If fuse F1 on the main circuit board is blown, replace it.
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Countermeasure
LH4-B800E