Issue
SCU 1284 won’t communicate to the controller when you turn power on to the device
Environment
SCU 1284
Cause
Product Support Services investigation of SCU12xx field failure returns has revealed that the significant majority of the returns are due to a failure of the RS-485 transceiver IC.
Most of the failures are also being described as initial installation failures or "out of the box" failures. Close examination of the failed circuits and the conditions that will prompt failure of the RS-485 IC currently in use on the SCU indicates a significant probability that many, if not most, of the failures are the result of momentarily connecting the TB1 terminal block onto the SCU header with it shifted 1 position to the right.
Connection of the TB1 block in a shifted manner will typically cause some relay buzzing noise prompting the installer to recognize the error and correct the position. Unfortunately the RS-485 transceiver will be damaged before you ever hear the relays buzz.
Other than TB1 misconnection, the predominant other candidate would be induced transients on the LAN. However, the frequent description of the problem occurring during installation or out-of-the-box tends to point toward TB1 misconnection.
Resolution
Caution your installation personnel to pay extra close attention to the connection of the TB1 terminal block in order to reduce the SCU failures being precipitated by misconnection. TAC will also be investigating RS-485 transceiver selection and the use of more tolerant versions, and possible end caps on TB1 to inhibit misconnection.
