104 72 30-26 Husqvarna service manual 19
Lower thread indicator
When the lower thread is almost at an end the machine gives a warning signal and a bobbin
flashes on the information display.
The lower thread indicator consists of an IR-diode that is reflected against a mirror on the
hub of the bobbin case, if the upper part of the bobbin is out of thread, and is received by a
photo transistor.
If the indicator does not work, it may be due to the indicator or the bobbin case being dirty
which makes it impossible for the IR-light to pass.
If the indicator still doesn’t work it should be replaced.
The fault may also be found on the circuit board, its connections or in some cases on the
LCD board.
You can check the indicator if you connect it to the circuit board (but don’t mount it) and
hold a mirror in front of it.
Photo transistor
(receiver)
IR-diode
(emitter)
Mirror
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