SLAC CPE Software Engineering Group
Stanford Linear Accelerator Center
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LCLS Switch Replacement

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Replacing a failed Controls Accelerator switch


Tools required:

  • Phillips screwdriver
  • Flat-head screwdriver
  • For organizing cables:
    • spare patch panel
    • numbered labels (one for each cable)
    • Velcro straps

*Two people would make things easier




NOTE: Only attempt to replace accelerator switches (names ending in -nw##) that are in "stacks" or installations containing more than one switch.


1 Get the spare switch that will be used for replacement

The spare switch is in building 005 room 114 

  • Unplug the power cord from the back of the switch
  • Unplug the fiber optic cables that plug into the front of the switch on the right. 
  • Unscrew the screws that go through the side mounting brackets and into the rack
2 Take the switch and required tools to failed switch Switches along the Linac (swh-sect*) are located in rack 3 in each sector.  Except for the RFHUT in S20 and S24.  The location of switches in service buildings can vary
3 Examine the status of the stack containing the failed switch

Failed switch will have either:

  • All LEDs off
  • Amber System LED

Switch is rebooting

  • System LED is blinking green
4 Confirm the state and the numbering of the other switches in the stack

Push the mode button on the bottom left until “STACK” LED is selected

  • All the switches in the stack will have one port LED blinking.  The top switch will be “1” and the second switch “2” and so on.
5 Power cycle the failed switch

Unplug the AC power

  • Wait a 20 seconds before plugging it back in
  • Skip to step 15 to see if the switch appears to be starting up correctly.

Power cycle failed if

  • System LED does not immediately come back on
  • System LED turns amber
6 Disconnect stack cables on the back of switch Loosen the thumbscrews (it may be necessary to use a flat head screwdriver to loosen the thumbscrews) and disconnect the stack cables from the failed switch
7 Disconnect cat6 cables on front of bad switch

The cat6 cables plugged into the front of the switch ports need to be plugged into the same ports on the replacement switch.

  • Unplug the cable from the failed switch and plug it into the corresponding port on the spare patch panel
  • Use the numbered labels to indicate the port number where the cable should be plugged in and then disconnect the cable

Switch ports are numbered like this (down then across):

  1  3  5  7  9 11

  2  4  6  8 10 12


Patch panel ports are usually numbered horizontally first:

  1  2  3  4  5  6  7  8

8 Take note of and remove any cables and modules plugged into the SFP ports on the right side of the switch

There are four ports on the right side of the switch that hold replaceable, modular transceivers called SFPs

  • If there are any fibers or SFPs remove them and make note of their placement (These should have captar labels on them)
  • These will also need to be returned to the same port number on the new switch. 
9 Clear any obstructions that might get in the way when removing the failed switch Use the Velcro ties if necessary
10 Support (if necessary) and remove the failed switch This is where an extra person is helpful
11 Install the replacement switch  
12  Reconnect the stack cables to the back of the switch

Example: Port 2 on all the switches always goes to lower switch port 1 unless you are the last switch in the stack which goes to port 1 on the top switch


13 Before reconnecting power to the replaced switch, be sure the other members of the stack are still functioning

Repeat the stack number confirmation process from step 4

14 Reconnect the power cable and watch the system boot up The System LED on the switch should turn green as soon as power is restored.  The other LEDs on the left will turn green shortly after.  The System LED should then start blinking while the switch conducts its power on self test.  During POST, the port status LEDs on the top of the switch will turn amber and then turn off when the test is complete
15 Re-check the stack numbering to make sure the replacement switch was properly configured during the boot process

Repeat the stack number confirmation process from step 4

If the numbering is not correct then ask the control room to escalate the problem.

16 Re-connect the twisted pair cables, and SFP modules and fiber cables (if any)

The cables must be plugged back into the same ports they were originally plugged into

The port status LEDs will turn green and start flashing as each active cable is connected –***Note not all cables will be active

17 Follow the appropriate procedures to make sure all critical devices are visible on the network after the replacement is complete

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Created by: Ken Brobeck  21-Jul-2009

Modified: 21-Jul-2009