SMD Device not removing

Hey Guys

I've done my research on how to remove SMD devices from a PCB motherboard and brought a T8280 PREHEATING STATION and 852D SMD station. I understand you have to preheat the motherboard to around 120C-150C and use the hot air gun to make the device loose so then you can remove it. I still can't remove any SMD device on the motherboard I've preheated the board to 170C and the hot air gun is at 250C with the air flow set to about 1/3. I cant even remove the small capacitors with 3 pins. I'm certain im using the right temperatures but I don't know where Im going wrong. Also the board is a acer laptop motherboard

Thanks

SM components are normally glued in place as well, tricky things to remove.

I'm certain im using the right temperatures but I don't know where Im going wrong.

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Can you melt solder? It should turn color, (shiny) when melted.

The glue will usually shear when the device is twisted.

Make sure the solder is melted.