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The MODs described below bonds DC negative to Earth Ground which will help protect the switch from Ground potential shifts between the tower and the AC Service Grounds.

We decided to do this modification to the original design because so many people do not do proper grounding and it will help protect your switch from ground current.

If the MFG date of your switch is after September 9th 2016 then this modification was done.

Since implementing this modification to the design we have not received a single unit that was modified returned for RMA repair damaged from ground current.

Even if you do this modification it is recommended to read our posts on proper grounding and always bond tower ground rods to electrical service ground rods.

Here are all our posts on grounding:
viewtopic.php?f=30&t=1816
viewtopic.php?f=30&t=188
viewtopic.php?f=30&t=1429
viewtopic.php?f=17&t=1786&start=30#p13447
https://community.ubnt.com/t5/airFiber/ ... rue#M31070

If you have a Rev F board or newer you can easily test if this MOD is done in your switch using an Ohmmeter and measure resistance between PIN 5 of the serial console port and the ESD shielding on the RJ45 stack . It should read near 0 Ohms meaning the MOD was done.

If a Rev E or older board and a DC powered switch you can measure Ohms between the DC terminal and the ESD shielding which should yield close to 0 Ohms which means the MOD was done.

If you have a Rev E or older unit MFG before 9/9/2016 then it is harder to check for and would require the chassis to be opened and inspected, see pictures below.

If you check with your local electronics supplier you should be able to purchase a 0 Ohm Resistor or Jumper Block to solder in place, should be at least capable of 10 Amps. Another option is to solder piece of copper or copper wire between the pads.

This is the 0 Ohm Resistor we use and suggest:
Digikey part: http://www.digikey.com/product-detail/e ... ND/5118869


THIS SHOULD ONLY BE ATTEMPTED IF YOU ARE WILLING TO BREAK WARRANTY SEAL VOIDING YOUR WARRANTY AND YOU ARE CAPABLE/QUALIFIED OF PERFORMING SUCH MODIFICATIONS. WE ARE NOT RESPONSIBLE IF YOU DESTROY YOUR SWITCH.

CLICK ON IMAGES BELOW TO VIEW FULL SIZE

WS-12-250-XX Rev A-E


WS-12-250-XX Rev F


WS-6-MINI Rev A-F


WS-8-150-DC Rev F


WS-12-250A/B


WS-24-400A/B

Hello,

Just to be sure : i have a PCB REV E, but it looks like your picture of the REV F (i have the two caps C18 and C94)





Ohmmeter says there is no link between ESD shielding on the RJ45 stack and Neg DC connector.

Should i apply the MOD as if i had a PCB REV F ?

Thank you

alexishh wrote:Just to be sure : i have a PCB REV E, but it looks like your picture of the REV F (i have the two caps C18 and C94)

Nope, that is a Rev F, clear states it on the board.

So yes, apply the MOD if you want and follow the instructions as it is a Rev F board.

Excuce me, "where" i can see the MFG date ??
Thanks!.

oxigeno2020 wrote:Excuce me, "where" i can see the MFG date ??
Thanks!.

Well it was on the original box label but you probably do not have that anymore.

Does the picture labeled WS-12-250A/B show how to modify the WS-12-250A Rev C switches?

Yes. if you have any other questions, feel free to email Chris or I with them.

Thank you

Why is it when I soldered a jumper across the pads marked C18, the power LED stopped lighting up? Is that normal? The power LED lit up again once I removed that jumper. The switches that did that are WS-12-250-AC Rev E.