Dear Stan,
I have some bad news for you.
Due to a combination of the very complex winding in place bobbin system and
the plastic gears that ran it. the repair you'll need will take Around $50 in
parts and more in labor. There are 2 gears under the area of the bobin winder,
you have teeth missing from one or both of the gears.This is a conastant
problem with these machines #600 &700 series Singers. Some old time mecanics
dubbed them the Touch and Jam!
I'm a vintage sewing machine collector and can fix most problems on older
machines but not these!
The valueof these on the market is low on average around $40 to 50 dollars{
Except a recondtioned one from a deale}r and I would not recomend buying one.
The plasic gears become dry and fragile with age even if the machine is not
used.
It's time to get your lady a New machine. the New ones are easier to use. Or
buy a top of the line older used machine.
I am not a dealer and have no afiliation with any sewing Co. I have just had
lots of experiance with these machines.
hallie In Miami