Cisco SG 100D-08 gigabit switch - No power

[benV]

Hi,

I found in the trash a Cisco SG 100D-08 gigabit switch like new but with absolutly no power at all. The power supply is ok and delivered 12 V. It seems that there's no fuse on board and in fact, i don't know where to start and what to check first. I already fixed some monitors with badcaps and i have a multimeter.

Here are both sides of the board.

Thanks for your help.

[mariushm]

Re: Cisco SG 100D-08 gigabit switch - No power

You have two (or more, but i only spot 2) switching regulators on the board.

You can trace the traces on the board from the power jack, going down to that capacitor and there on the right it's a switching regulator chip. It's easy to spot because switching regulators usually require a diode and an inductor. The first regulator has the D2, L2 pair and the second one has L1 and D1 pair.
Those chips with 10 pins are the regulators.
The first regulator that power goes to is the one on the bottom, the one with L1 / D1 ... if that one doesn't output voltage then the second regulator with L2/D2 it may be dead as it gets no input voltage from the first regulator.

Start by plugging the switch then measure the voltage across that main capacitor C6, then remove the power and check those smd diodes to see if they're shorted or not.

Read what's written on those regulator chips, write everything here, and in the meantime look up for the IC datasheet on findchips.com or digikey.com / newark.com (search for the numbers not just the complete line of text, ex if it says ba971 search for 971 separately) in "switching regulators" or "voltage regulators" .. you can filter by smd and number of pins

You can then determine which one is the input voltage pin (but you can tell this one by following the traces from previous regulator or from the jack) and the voltage output pin (hint - the output is usually going through the inductor so put a lead on a ground trace/pin/screw and probe the inductor solder points with the meter on voltage, while switch is powered)

[sebr]

Re: Cisco SG 100D-08 gigabit switch - No power

I just got two of these units on my desk, same symptoms - completely dead but wall wart works fine. Both are H/W Rev. 00. After cracking them open and doing some basic troubleshooting it turned out pretty soon that in both switches the faulty item was L3 which has gone high impedance. So I simply bridged it and units work fine now.
While I had the thing cracked open already, I replaced the (only) cap which in my case was an Ltec. Not neccessary but gives a better feeling to me