The reset button disables your pitch control and allows the turntable to rotate at TRUE "0" (zero). FYI, these turntables were NOT made for DJing. They were made for radio, studio, and high end home use. They became DJ turntables, because they were perfectly built for the trade. So, the pitch reset button is more of a function best suited for radio stations or a producer who needs to record or play at a true zero speed.
Now, on to your question...
More than likely you just have to calibrate your pitch control. There are various videos on YouTube on how to do this properly. Just do a search CALIBRATING 1200s or similar. FYI, all the Technics SL1200/1210 MK series are the same inside. MK2, MK3, MK5 - so don't worry if you only find videos on calibrating MK2's or MK5s - works the same on all the models.
- TERMiNAL OPTiCwww.DJPROLAB.com