The error code of F1-90 means the following;
Communication trouble between the decurler and the downstream units. OR possibly;
Communication trouble between the decurler and the units connected to the downstream of the decurler.
CAUSE; Noise on the communication line, control PWB trouble, disconnection of connector or harness.
REMEDY; Turn OFF/ON the power. Check connection of the connector between the decurler unit and the downstream units of the decurler. Replace the control PWB of the downstream units of the decurler.
A complete error code list can be found here; Error Codes Sharp MXM1204 page 11
Use the < and > to go through the complete list.