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Electronics => Repair => Topic started by: Pete66 on November 30, 2019, 07:31:59 am

Title: Repair of a Cisco SG300 28P POE switch
Post by: Pete66 on November 30, 2019, 07:31:59 am

My Cisco SG300 28port POE switch crapped out on me.  Can't connect to it unless I go through the console and when I do it keeps giving POE errors.  This happened after a power outage so I opened it up to have a look inside.  The first picture is the inside of the switch. Power supply voltages are good.  The problem is in the board on top this is the POE board shown in pictures 2 and 3.

In the 2nd picture I have removed Q16 mosfet (N2NF10) it was shorted, fuse F45 was open.  Also diodes D63 & D64 shorted but tested fine when removed. 
On the back side Q46 mosfet  (also N2NF10)  shorted along with diode pack D58 (BOV23S) has an open diode inside and capacitor c165 open.  D55 and D54 have also been removed to be tested and they are fine.

Now even though I removed the shorted mosfets the traces are still shorted on the board.  So I removed U6 POE Chip (PD69012) and the short on the board is gone.

So at this time I need to find a source for the PD69012 POE chip.  I ordered a couple from Ali Express but who knows if they are real. 
In case they turn out to be fakes does anyone know where I can get this chip?

Also the fuse F45 has only an "L" marking.  Anyone know what the value might be?  I'm guessing maybe 500ma but if it's littlefuse brand it could be 1.75A?


Title: Re: Repair of a Cisco SG300 28P POE switch
Post by: kripton2035 on November 30, 2019, 07:34:44 am
you can find this chip by all major suppliers, but in big quantities ... (

or try to ask for a sample by the manufacturer : (

but as it is "not recommended for new design" may be difficult to get.
Title: Re: Repair of a Cisco SG300 28P POE switch
Post by: Pete66 on November 30, 2019, 07:53:19 am
Thanks for the links.  The price is very expensive.
I sent a request for samples we'll see what happens.

If anyone else knows any other sources let me know.
I'm also still trying to figure out what rating the fuse F45 is.

There are 28 SMD fuses in picture 2  they are all the same.  Anyone have any ides what the Fuse rating is for these fuses.  They all have an "L" marking.

Title: Re: Repair of a Cisco SG300 28P POE switch
Post by: Pete66 on December 06, 2019, 05:54:46 pm
I ordered 10 for $23 from ali express.   Im hoping at least some of them will be good.  They are probably pulls or since these are made in China to begin with they could be new.

I am still trying to find the fuse.  If you look at picture 2 there are SMD fuses labeled wit an "L".

Anyone know what the value is or what type of fuse that is?

Title: Re: Repair of a Cisco SG300 28P POE switch
Post by: james_s on December 06, 2019, 07:39:35 pm
Sometimes you get lucky with random ICs like that from China, that's where all the production is these days so that's also where all the surplus is. Vintage parts are likely to be fake but there is also a lot of more recent stuff that is surplus from manufacturing products, just like we used to have in the US when stuff was built here.

For the fuse I think I would just try to work out a reasonable value based on what can be deduced from looking at the design. You should be able to get a reasonable idea of the power it will need to carry, and then knowing the voltage you can estimate the fuse. It shouldn't be very critical, unlike a branch circuit in a house for example where it's easy to overload the circuit, the situation here is likely to be a case of everything is fine, or something is shorted and the fuse is there to prevent catastrophic damage. You could also just fix the rest of the thing and then measure the current across the fuse pads and choose a fuse based on that.
Title: Re: Repair of a Cisco SG300 28P POE switch
Post by: Pete66 on December 22, 2019, 01:52:36 am

Well the PD69012 POE IC's came from Ali Express Yesterday pictured below. I ordered 10 for $20 total shipped.  They are brand new and work like a charm.  My switch is back in service.  I swear Ill never criticize Ali again. 

The switch has 24 POE ports and uses two PD69012 ICs.  Each IC handles 12 ports. It turns out both of them were fried and I had to replace both. 
I tested each port 8 at a time with 8 POE cameras and they are working fine.

Also I was using a temporary switch (Trendnet 8 port POE) until I was able to fix the Cisco switch.  A week before I fixed the Cisco switch my temporary one crapped out also.  LOL.  That one used an LTC4266 POE chip.  I was able to buy that chip from Digikey and I fixed that one also.

So I guess these POE chips fail often.  If you have POE switches I would open them up and see what ICs they use and order a couple of spares from Ali Express /ebay or Digikey because when they blow out you may not be able to find the part.