When triggering the bell zone on the CY-13R, be sure to use the neck/shoulder of the stick and give it a good solid strike. The bell zone it is slightly less sensitive than the bow zone and if you tap on it lightly using the tip of the stick, the bell will most likely not be detected by the TD-07.
Confirm that the CY-13R is positioned correctly on the stand. Similar to the crash (CY-12C) and hihat (VH-10) pads, the Roland stamped logo should be on the opposite side and legible from left to right from the player's view. If the logo is on its side or upside-down, reposition it correctly.
Next, check the cable connections:
The cable labeled as "RD" should be connected to the BOW/EDGE output on the CY-13R.
The cable labeled as "CR2" should be connected to the BELL output on the CY-13R.
Be sure to insert the cables completely and securely into the outputs on the pad.
Then confirm the Crash 2 Usage parameter is set to "BELL" in the TD-07 with the steps in this link: TD-07: Crash 2 (CR2 Cable) Usage