Reconfigure the control link port to a different SPC, move the cable and reboot both nodes. Is the control link up?
Yes - Possible hardware issue with SPC. Continue to Step 8.
No - Continue to Step 7.
If the Control Link is SFP-type port, change the transceiver on both ends. Ensure that the transceivers are same type (LX, SX, etc.) and that they are Juniper-branded parts. Is the Control Link up now?
Yes - Possible faulty transceiver issue. RMA may be required for the transceivers. Continue to Step 8.