Field Notice: FN - 63723 - CISCO39xx and VG350 Fans Might Fail Due to Capacitor Issue - Replace on Failure

Notice

THIS FIELD NOTICE IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTY OF MERCHANTABILITY. YOUR USE OF THE INFORMATION ON THE FIELD NOTICE OR MATERIALS LINKED FROM THE FIELD NOTICE IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS FIELD NOTICE AT ANY TIME.

Revision History

Products Affected

Defect Information

Problem Description

One or more fans in a 39XX or VG350 fan tray might fail or run at less than design Revolutions Per Minute (RPM) criteria due to a component issue. Routers that experience this issue should be monitored for temperature alarms. Customer's routers might experience this issue and not be aware since temperature or low fan speed alarms might not be generated.

Many platforms can operate for extended duration with fan alarms and not experience temperature alarms. Temperature alarms should be given higher precedence (versus fan low speed alarm) and immediate fan tray replacement is required. Fan service should be scheduled during the next available maintenance window, and the fan tray in the router should be replaced.

Background

Some of the fans provided by a specific supplier might have a faulty capacitor. The capacitor might deteriorate over time and eventually fail, which causes a loss of fan speed control.

Problem Symptom

A capacitor failure (from a specific supplier) in a 39XX or VG350 fan might cause the fan to run at a slow speed. This might not trigger a fan failure alarm. If a fan alarm is not generated, the customer might receive a router over temperature alarm. In either case, the sho env table command should be executed in order to review what the actual fan speeds are in operation.

Fan Failure Alarm

This messages repeats on the console if a fan failure alarm is generated:

"Dec 4 03:56:41.194: %ENVMON-4-ONE_FAN_LOW_RPM: Warning: Fan 2 is running at low RPM. Rotation speed is now high for all other fans. Fan Tray replacement is recommended."

Note: There are five fans in the 3900 fan tray. For this message, Fan 1, Fan 2, Fan 3, Fan 4, or Fan 5 will be identified in the low RPM warning message. If multiple fans have failed, each fan that fails will be reported. It is possible for the low fan speed condition to oscillate in and out of the range of the threshold to trigger an alarm. With this behavior, the message might be generated erratically if the fan speed increases above the lower threshold limit.

The sho env table command should be executed and the fan speeds reviewed. Output should look similar to this:

SYSTEM FAN STATUS
=================
Fan 1 OK, fan level 5, High speed setting, 6656 RPM, 100% PWM
Fan 2 Low RPM
Fan 3 OK, fan level 5, High speed setting, 6744 RPM, 100% PWM
Fan 4 OK, fan level 5, High speed setting, 1646 RPM, 100% PWM
Fan 5 OK, fan level 5, High speed setting, 7105 RPM, 100% PWM

Fan 2 is reported in a low RPM and failed state. The other fans have been set to the maximum speed setting. Note that Fan 4 runs at a much lower fan speed than the other fans even though it has not raised an alarm. Fan 4 is actually not ok. Fan speeds shown in the output of the sho env table should be compared to the minimum fan speed settings shown in the table included in this section. If the fan speed reported for a specific level is less than the value shown in the table, the fan capacitor has failed.

Temperature Alarm

These messages repeat on the console if an over temperature alarm is generated.

3925/45 "Jan 9 13:11:46.728: %ENVMON-2-CPU_CRITICAL_OVERTEMP: Critical: CPU temperature 127C exceeds 115C threshold. Please resolve system cooling immediately to prevent system damage."

3925/45e "ENVMON-1-CPU_CORE_WARNING_OVERTEMP Warning: CPU core is very hot value = 20. It exceeds threshold 24. Please resolve system cooling immediately to prevent system damage."

The sho env table command should be executed and the fan speeds reviewed. Output should look similar to this:

SYSTEM FAN STATUS
=================
Fan 1 OK, fan level 3, Medium speed setting, 592 RPM, 62% PWM
Fan 2 OK, fan level 3, Medium speed setting, 503 RPM, 62% PWM
Fan 3 OK, fan level 3, Medium speed setting, 760 RPM, 62% PWM
Fan 4 OK, fan level 3, Medium speed setting, 414 RPM, 62% PWM
Fan 5 OK, fan level 3, Medium speed setting, 5381 RPM, 62% PWM

Speeds for Fans 1 through 4 are very low while the speed for Fan 5 is normal. The fan speed level of 3 is set by the temperature of the intake air as measured by the router. The speeds for Fans 1 through 4 are low but are not low enough to generate a fan alarm for a low RPM condition. This means those fans are not ok. Fan speeds shown in the output of the sho env table should be compared to the minimum fan speed settings shown in the table. If the fan speed reported for a specific level is less than the value shown in the table, the fan capacitor has failed.

39XX and VG350 Fan Speed Minimum Values

Workaround/Solution

No workaround is available. The fan tray must be replaced via the Return Material Authorization (RMA) process.

Actions to Take

• Determine if the 3900 router or its fan tray assembly is susceptible to this failure mechanism with the procedure shown in the "How to Identify Affected Products" section.
• For routers or fan tray assemblies that are determined to be "Affected" or generate over temperature or fan fail alarms, query the router with the sho env table command in order to determine if the fans operate correctly and examine the fan speeds.
• If any fan's RPM is less than the minimum value listed in the table, replace the fan tray.

How To Identify Affected Products

Verification of susceptible fans should be done through the Fan Assembly Serial Number database. All Fan Assembly Serial Numbers must be checked and validated as susceptible before replacement of the fan assembly can take place.

Chassis Serial Number Lookup for Chassis that might have shipped with affected Fan Assemblies.

Note: The first three letters of Chassis Serial Numbers begin with FCZ, FHK, FGL, or FTX.

Fan Assembly Serial Number Lookup for Fan Assemblies that might be affected.

All Fan Assemblies must be verified through this link. The Chassis serial number lookup is to help narrow down which units might have been shipped with affected Fan Assemblies only.

Note: The first three letters of Fan Assembly Serial numbers begin with FOX.

When you physically check the Serial Numbers of the Fan Assemblies, refer to the "Replacing a Fan Tray or Air Filter" section of the Installation Guide to remove and replace the Fan Assembly.

Additional Information

E118040

For More Information

If you require further assistance, or if you have any further questions regarding this field notice, please contact the Cisco Systems Technical Assistance Center (TAC) by one of the following methods:

• Open a service request on Cisco.com
• By email
• By telephone

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