A lift in one (1) of the blocks of a condominium was reported to have failed. Upon checking, the lift vendor claimed that it was raining at the time of the lift failure and lightning had caused the motherboard, three (3) module calling PCBs, the car top PCB, and the door controller of the lift to be damaged.
Damage Analysis & Interpretation:
Burn marks were found around the pins of High-EPROM.
Burn marks and heavy soot deposits were also observed on the rear of the three (3) module calling PCBs.
The housing of the relay of the car top PCB, which controlled the cabin lights, was partially melted.
Burn marks were found around the optocouplers of the door controller.
Possibility of Failure Due to Lightning-Induced Transient
The lift motor room is located on top of the building. Hence, it is susceptible to lightning. However, lightning stroke report shows that there was no lightning activity in the vicinity on the reported date of loss.
A single-line diagram was created based on the on-site inspection and information from the technician.
Apart from tripping the MCCBs, the lightning-induced transient, if there was any, would have travelled and affected the components, such as the transformer, inverter, and AC/DC power supply, before damaging the claimed components. However, none of these components were damaged.
Any lightning-induced transient would have also entered and damaged the main PCB through the incoming power supply. However, no burn marks or damage was found around the incoming circuit of the PCB.
Therefore, the lift components were not damaged due to lightning activity.
Failure Due to a Foreign Object
Block diagrams of the affected PCBs were obtained and studied, as shown below.
The damage analysis revealed that the door controller sustained the most damage, followed by the car top PCB, the three (3) module calling PCBs, and the motherboard. The initial failure appears to have originated from the door controller.
Further microscopic examination revealed three (3) of the four (4) legs of the optocoupler were melted, while loose wires were found to have stuck between the legs.
The wires were foreign to the door controller and did not belong to any of its electronic components. The wires caused a short-circuit and arcing between the legs of the optocoupler, causing excessive heat and melting. The fault current then travelled back to the upstream circuit to affect the car top PCB, followed by the three (3) module calling PCBs and subsequently the motherboard. The travel path is shown below.
Therefore, we have concluded that the damage to the lift components was due to the introduction of a foreign object.
*Identities in this case study article have been altered to protect the individual’s privacy.
