Brother PC 3000 - Manual (Page 28)

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With the accessory compartment off the machine, the feed dog
adjustment lever can be seen on the base of the sewing machine.
Sliding the lever to the right will lower the feed dogs, for example
during button sewing.
If you wish to continue sewing normally, slide the lever to the left
in order to raise the feed dogs.
The feed dogs cannot be raised if the balance wheel does not
turn, even if the lever is slid to the left.
FEED DOGS