Summary:
The TN52FCD fan tray assembly on the OptiX OSN 8800 T32/T64 subrack occasionally has its fans stopped, leading to a FAN_FAIL or FAN_FAULT alarm on the subrack.
[Problem Description]
Trigger condition:
This problem occurs when the following conditions are met:
- The TN52FCD fan tray assembly on the OptiX OSN 8800 T32/T64 subrack works in auto speed mode and the fans rotate at the lowest speed.
- The optical coupler that is used to convert the PWM signal inside the fan tray assembly is provided by Renesas Electronics in lot 146.
NOTE
Altogether 492 fan tray assemblies (BOM code: 02120495) are equipped with Renesas optical couplers of this delivery lot. The table below shows the distribution of these optical couplers.
Symptom:
- Symptom 1: A FAN_FAIL or FAN_FAULT alarm is present on the U2000 and the STAT indicator on the fan tray assembly is steady red or orange. Physically, the STAT indicator is steady red when the FAN_FAIL alarm is present and is steady orange when FAN_FAULT is present. In addition, the noise generated by the fans is sometimes large but sometimes small, alternating at intervals of 3 to 5 seconds. In general, the noise is less than 85 dB.
- Symptom 2: A FAN_FAIL or FAN_FAULT alarm is present on the U2000 and the fans inside the fan tray assembly have stopped working. Physically, the STAT indicator is steady orange when the FAN_FAULT alarm is present and is steady red when FAN_FAIL is present.
Identification method:
To determine whether the problem corresponds to this warning notice, perform the following steps:
1. On the U2000, check that a FAN_FAIL or FAN_FAULT alarm is reported for the fan tray assembly.
2. Check that the STAT indicator (in the red circle in the figure below) on the fan tray assembly is steady red or orange. (Skip this step if you are not in the equipment room.)
3. Change Fan Speed Mode to Adjustable Speed Mode and set the fan rotation speed to the Medium Speed or Medium-High Speed. Then check whether the alarm has cleared. If the alarm has cleared, the problem corresponds to this warning notice. If the alarm persists, the problem does not correspond to this warning notice, but is related to other fan faults.
[Root Cause]
The PWM signal, which is used to adjust the fan rotation speed, generated by the logic of the fan tray assembly is converted by the optical coupler of the fan tray assembly before it is sent to the fans. A small number of OptiX OSN 8800 T32/T64 subrack fan tray assemblies are equipped with Renesas optical couplers delivered in lot 146, while these optical couplers have a defect to introduce a large attenuation. As a result, the duty cycle of the PWM signal is large and the PWM signal is attenuated greatly. When the system automatically adjusts the fan rotation speed to the lowest speed based on the received PWM signal, the fans are likely to stop working. When the fans stop, a FAN_FAIL or FAN_FAULT alarm is generated.
[Impact and Risk]
This problem does not affect the normal operation of the OptiX OSN 8800 T32/T64 subrack.
1. A FAN_FAIL or FAN_FAULT alarm is reported only when the system instructs the fans to rotate at the lowest speed.
2. If the system temperature increases after the fans stop working, the system will instruct the fans to rotate at a higher speed. When receiving the instruction, the fans will start rotating and correctly adjust their fan speed to ensure efficient heat dissipation.
This problem affects user experience. The FAN_FAIL or FAN_FAULT alarm and the lit STAT indicator will induce the customer to believe that a fan failure or fault has occurred.
[Measures and Solutions]
Recovery measures:
On the U2000, change the Fan Speed Mode to Adjustable Speed Mode and set the fan rotation speed to Medium Speed or Medium-High Speed.
Workarounds:
None.
Preventive measures:
On the U2000, change the Fan Speed Mode to Adjustable Speed Mode and set the fan rotation speed to Medium Speed or Medium-High Speed.If the cumstors do not accept the measure,replace the defective fan tray assembly.
Material handling after replacement:
The replaced fan tray assembly is scrapped.
[Attachment]
List of Delivered Optical Couplers (02120495) with Renesas Optical Couplers Delivered in Lot 146
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