That's good to know. I've had customers bring their Brother machines in with the F4 error, and we honestly didn't know, so told them to take it to a Brother dealer. When machines like yours come in, we try to fix you up on the spot, because we know you probably don't want to leave it and spend $70 on a service. It's usually something simple, that we wouldn't charge you for. Or something electronic that's only privy to Brother dealers.