I believe you probably have a Bernina Favorit. A Favorit is an early mechanical Bernina sewing machine and, to Bernina vintage lovers, is a keeper. Favorits are the flat-bed version, not the free-arm version, but is a wonderful machine nonetheless. If you search the internet using:
the word "Manual"
(ie Bernina 640 Manual)
you might have some luck finding a manual.
Or, you can join the Yahoo BerninaThirtySomethings group
, where older manuals are available in the Files section. In addition, you will have access to a wonderful resource of Bernina users/lovers including conversations on using, maintaining, repairing, and assorted other advice about your older Bernina.
The first thing you should probably do is pick up a good quality sewing machine oil (Bernina oil for CB Hook is recommended--however, never use 3-in-1, WD-40, cooking oil, or the old oil can that you might find in the machine's accessory box). Consult the owner's manual in the Maintenance section to clean and oil your machine. If the machine has not been used in several years, the motor may sound like it is straining to move the mechanical parts. Most likely, the old oil has dried out and is sticking things together. Do not force the motor to move things without first cleaning and oiling the machine.
Remove the top cover and swing open the cover on the left side where the lightbulb is located. Gently hand rotate the handwheel and while watching the moving metal parts, apply ONLY one-two drops of oil every place that metal rubs against metal. (Sometimes the oil ports are marked with red paint as a guide, but some machines are not marked.) Use only 1-2 drops at a time. Do NOT over-oil as too much oil can be as damaging as no oil. Gently move all the levers and dials and oil those moving parts as well. Do NOT oil the white plastic gears, the belt, or the large round metal cams (which your machine may or may not have). Then, tilt your machine back and remove the bobbin & bobbincase and with a soft brush, remove any lint, dust. Then while hand-rotating the handwheel and moving the levers and knobs, apply oil to the moving parts under the machine. The feed dogs are usually a problem so be sure to test the feed dog knob. If anything seems to be sticky, resistant to movement, you can also direct hot air from a handheld hairdryer into the interior mechanism to help loosen things. Be sure to place a drop of oil on the bobbin hook in the bobbin area (the manual should show this).
If there is anything that is still sticky, then a few more drops of oil and the handheld hairdryer should be employed until things are moving well again.
A Bernina is a great machine for the sewing enthusiast, but only if it is maintained and cared for regularly. Cleaning and oiling should be performed approximately every 8-12 hours of constant sewing, or every time a bobbin is emptied, or at least every six months if not in frequent use.