One node board lights only its red LED and does not come up on the network.

Spike 2 node board shows only the red LED: shorted zener D9 killed regulator U9

Cause: Zener diode D9 had shorted and took out regulator U9, so the board had no 6 V supply. The 3.3 V rail was then held down by a failed microcontroller (U1).

Checks

• Measure the 6 V and 3.3 V rails on the dead node board.
• Check D9 for a short and U9 for output.
• If 3.3 V is still shorted after the regulator repair, suspect the microcontroller U1.

Fix

• Replace D9 and U9.
• Replace U1; the poster moved the microcontroller over from a donor node board.

Systems

• Spike 2
• Spike 2 - Classic

Source: Pinball Repair help group!! (Facebook group)