Please find the following step to replace digital scale for AC400 Dual machine

1) Remove two tank screws

2) Loose two tanks to have space to remove back cover, don't remove hose from the tanks

3) Open back cover to check wire

4) Remove loading plate to find scale unit under

5) Scale 

Keep a space on one end as overhang and arrow point down.

6) You must remove two screw under the machine bottom

7) Remove front blue cover

8) Find the scale wire plug into motherboard

9) Once the new scale wire plug into motherboard, try to put all screws and revert back to original. it should be done.