Canon Perfect Binder A1 Troubleshooting Manual page 112

[Note]: In conjunction with the movement of the Shutter [1] in the direction of arrow, the Dust buffer [2] coordinates. (below figure
[A]) If the Shutter [1] is moved further in the direction of arrow, the Dust buffer [2] moves away from the Shutter (below figure [B]).
Refer to the service manual for detail of the operation of the Shutter.
1-9) Repeat the step 1-8) for several times and check if the metal plate [1] of the Dust buffer is seen from the gap on the stack
rotation assembly.
If the metal plate is not seen, then the Hook arm may be fractured. Go to the step 2).
If the metal plate is seen, then the Hook arm is not fractured. The error results from another cause. Reassemble the parts in
reverse order of the step 1-7).
110