Weak vacuum at the nozzle prevents location teach.
If you suspect weak vacuum at the pick and place(PNP) nozzle, follow this procedure.
Check the input air regulator located inside the pneumatics box. The rightmost regulator should be set to 80 PSI.
Next check the hoses and fittings on the vacuum generator inside the pneumatics box.
In BPWin, go to Main Menu/Autohandler/Diagnostics/IO and Sensors, and turn on the vacuum. Go to the machine head assembly and put you finger on the end of the nozzle and monitor the vacuum value. The vacuum values on the I/O and Sensors Diagnostic dialog are a function of the vacuum switch. If the vacuum is weak, the switch will not trigger on. The vacuum voltage level must change more that 1.6 VDC to signify that a device is on the PNP nozzle. When this is achieved, the LED on the vacuum switch will turn on. The green LED on the IO and Sensors window will also turn on.
Remove the vacuum hose from the fitting on the right side of the vacuum block and place your finger on the end of the hose. If the vacuum feels strong, then suspect a leak in the vacuum block assembly If the vacuum feels weak, then suspect a problem upstream of the vacuum block, for example the vacuum valve could be leaking or sticking, these could be a split or cracked hose in the e-chain or the vacuum generator is worn-out.
The following diagrams show details about the pneumatic system, and details about the vacuum block.