First, connect your source to the TH685 and press Menu.
Choose Basic Menu > Picture mode > Game mode. This will turn on Fast Mode automatically, which has a low input lag.
If you are in the Advanced Menu, go to Picture > PictureMode > choose Game mode, or Picture > Advanced > Fast Mode to turn on this feature.
To enjoy lowest input lag, please note that when when Fast Mode is on:
1. Keystone can be adjusted, but it will increase input lag.
2. Overscan will be greyed out
3. Aspect ratio will be locked at 16:9
Also, Fast mode only supports 1080P 60Hz and 1080P 120Hz timing.