Needle keeps jumping back 4 bars on records

I believe someone mentioned that the anti-skate should be set the same as your counterweight. Unless you're a scratch DJ. then it should be set at zero.
Could the problem records be damaged or warped? Sometimes very small imperfections in a record's surface can cause needles to skip. You could try running the needle a little heavier. Maybe loosen the head shell and twist just barely counterclockwise and re-screw it back down. This gives the stylus a little more bite and may keep it from skipping back. Another idea maybe loosen and readjust the bearings on the tonearm assembly with a small flat head screwdriver.
The reason the other person's answer mentioned having the cables replaced is because sometimes people put the assembly back together and forget to set anti-skating where it should be and it ends up constantly pushing the tonearm out. If that is the case, I explain how to fix it here :http://www.fixya.com/support/t10831123-needle_skiping_back_stop_changed_hight . If you are handy with tools, it's not that hard. But you might give this a try just pull the tonearm with your hand to the center kind a hard and see if it clicks that may fix it.
another thing to try is a cleaning product called Gruv Glide. This stuff is awesome! It makes old records sound almost new again and really helps with tracking issues. Just make sure you do not spray it on the record. It comes with easy instructions.

anyone wanting to do repair work on it technics 1200 series motor board should check this out. It perfectly diagnosis problems and has replacement part numbers http://www.deckdoctor.com.au/TECHNIC%20SL1200%20PCB.pdf

I’m happy to help further over the phone at https://www.6ya.com/expert/erik_149c4c1c216e42f2

CHECK ANTI SKATING SETTING SHOULD BE SAME AS STYLUS FORCE ABOUT 3.ADJUST TONEARM HEIGHT SO IT IS PARALLEL TO RECORD WHEN PLAYING.HAS THE DECK HAD NEW PHONO CABLE FITTED RECENTLY IF SO THIS WILL BE THE CAUSE GET IT DONE PROPERLY.