Put some grease onto the back of the adaptor that is used to spin smaller substrate then put the adaptor onto the substrate holder, place the wafer ontop of the adaptor then turn on the vacuum to see if you can defeat the vacuum interlock. If adaptor is not exist, remove the substrate holder to the point that you can put your thumb onto shaft that connecting the substrate holder and the vacuum inlet then turn on the vacuum button (there's an elbow joint @ the bottom of the shaft that the substrate holder's connected to, this is where the resist tend to accumulate) ..... remove the vacuum line, fill the shaft with liquid, if liquid comes out of the vacuum inlet then you got no blockage. huy I took the parts out in the pathway and cleaned them so it is less likely that there is some blockage than leakage. Any good way to check the leakage? And I confirmed that the external vacuum pump and the vacuum sensor on the spin coater are all right. Thank you. Jia