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FAQ - Failure in diode on CXL16 board cause continuous reset on OSN 2500.

Publication Date:  2012-07-25 Views:  52 Downloads:  0
Issue Description
On OSN 2500 with software version 5.21.18.50 P01 ocurred continuous reset. In node the power supply is normal but the equipment still present resets. We checked the PIU on slot 22, It is normal but the PIU in the slot 23 has fuse broken. We must changed the fuse but in each reset the fuse was broken.

Alarm Information
Null

Handling Process
It is supposed that root cause is the combiner diode of some board of this OSN2500 failure, and the diode reversing conducted.

  1. Confirm failure phenomenon before operation: disconnect power cable from PIU A, and measure voltage from INPUT terminal of PIU A when there is another one way power supply to the equipment(PIU B),the voltage should almost be 0V at normal situation; if there is the voltage, means abnormality, do next step;
  2. Pull out one by one to each board of the rest of the slots, each pulled out a board with a multimeter voltage measurement at INPUT terminal of PIU A, which is already unplugged the power cable, and record it;
  3. Each pull out a board to observe this slot backplane connector, board connector and the device nearby the connector with or without color darker or burned phenomenon. If still has  voltage, and no other anomalies, can insert the board back and continue to operate next board;
  4. When pulled out a board, measure input terminal of PIU A and the voltage disappears. Sure that this board has problem. Replace it or do not plug it back;
  5. Measure input terminal of PIU A again and confirm the voltage disappears;
  6. Connect power cable for PIU A, and disconnect power cable for PIU B, and measure INPUT terminal of PIU B, check whether there is voltage from PIU B, if it is, may also exist other board failure;
  7. Following the steps above, and then test again, until identify abnormal board and replace it or not plug it back;

When we pulled out board by board, we found that CXL16 board on slot 10 had diode's damaged. 


Root Cause

We found the abnormal event in PIU’s. If turn off the breaker in PDU A and check the voltage in PIU A, still has a voltage on input the PIU A. Also, we disconnect directly the power cable  from PIU A(slot 22), check directly the voltage in power cable and multimeter show 0 v (normal value), but check voltage on input from PIU A and found with multimeter -54 v. This value was not normal if the power cable was disconnected from PIU A. For this test the PIU B always be connect to PDU B (turn on).

The same problem ocurred with the other PIU B(slot 23). If turn off the breaker in PDU B and check the voltage in PIU B, still has a voltage on input the PIU B. Also, we disconnect directly the power cable  from PIU B(slot 23), check directly the voltage in power cable and multimeter show 0 v (normal value), but check voltage on input from PIU B and found with multimeter -55 v. This value was not normal if the power cable was disconnected from PIU B. For this test the PIU A always be connect to PDU A(turn on).

The PIU's not show POWER_ABN alarm when disconnect the power cable from each PIU.
 



Suggestions
Firstly, you can check many cases for found problem:

1. You must check  possible ground problem on site.
2. Check all PIU boards.
3. Check voltage on PDU.
4. Check all boards on equipment
5. Check backplane.

END