Brother BAS-311G - Upper Thread Length is Irregular; Machine Does Not Operate When Powered On

8. ELECTRICAL MECHANISM
135
BAS-311G, BAS-326G
Problem #21 Thread is not trimmed.
Cause Inspection/Remedy/Adjustment Replacement if a malfunction
1. Incorrect mechanism adjustment Adjust the thread trimming mechanism while
refer to “7-17. Adjusting the thread trimming cam
position”.
(If it is clear that the thread trimming mechanism
is not operating, carry out inspections 2. and 3.
below.)
2. Poor connector contact Check that connector P1 (MAIN) is inserted into
the PMD P.C. board.
3. Malfunction of thread trimming
solenoid
Disconnect connector P6 (SOL1) from the PMD
P.C. board, and measure the resistance between
pins 3-6 of the cord-side connector.
OK if 6 − 8 Ω
Thread trimming solenoid
4. Malfunction of tension release
solenoid/digital tension
Disconnect connector P7 (SOL2) from the PMD
P.C. board, and measure the resistance between
pins 1-2 of the cord-side connector.
OK if 6 − 8 Ω
Tension release solenoid/
digital tension solenoid
5. Malfunction of PMD P.C. board 1) With connector P6 (SOL1) connected to the
PMD P.C. board, turn on the power and carry
out sewing, and measure the voltage
between pins 3-6 of connector P6 (SOL1).
OK if voltage is output momentarily at the
sewing end.
2) With connector P7 (SOL2) connected to the
PMD P.C. board, turn on the power and carry
out sewing, and measure the voltage
between pins 1-2 of connector P7 (SOL2).
OK if voltage is output momentarily at the
sewing end.
PMD P.C. board
4889Q
4890Q
4891Q