Teardown: Dead GbE switch

-December 06, 2016

I seem to go through a lot of Ethernet switches, as longstanding teardown readers will likely concur. Part of the reason, I realize, is that I currently have five different five- and eight-port GbE switches in operation in various areas of my house (which may sound like a lot, but is actually a decrease from times past, when I was using more wired-vs-wireless Ethernet-connected devices). So some of it is pure probability. Some of it, too, can be chalked up to the "Act of God" factor ... in just the past year-plus, I've gotten two units zapped by close-proximity lightning bolts. And some of it is likely geriatric in nature; the other two recent-times teardown victims had been in occasional-to-steady use for a number of years.

But part of the reason, I suspect, has to do with economics. My admitted tendency is to wait to pick up switches until they're deeply discounted by sales, rebates, and the like, then purchase several at once as spares. Doing so saves me money in the short run, but I can't help but wonder if spending more cash upfront on more robust models might be more economical in the long run (or, at minimum, keep landfills from getting clogged with my dead hardware). Then again, though, my email-receipt archive informs me that this particular metal-chassis teardown victim is, like its plastic-chassis TEG-S8 sibling that I dissected back in January 2014, nearly a decade old. Maybe I'm just asking too much?

This time we're looking at TRENDnet's now-discontinued TEG-S80TXE, an eight-port GbE switch. One recent morning I awoke to find that a notable percentage of my LAN's wired clients, including several wireless access points, had mysteriously gone offline. A trip downstairs to my network nexus, the furnace room, revealed that only the TEG-S80TXE's power LED was still illuminated; the entire front panel array of activity and protocol LEDs was dark. A couple of power-cycle attempts were for naught. The switch (like a well-known parrot) wasn't simply resting; it was deceased.

I'll begin with a few exterior-view shots, followed by a closeup of the underside-located product label:

The removal of two visible Phillips head screws enables straightforward slide-off of the top panel, thereby exposing the solitary system PCB to view:

Click to enlarge.

I'd expected a similar parts allocation to that in the TEG-S8, given their similar naming and age. I couldn't have been more wrong. In retrospect, though, had I done a line-by-line comparison of the two switches' specifications, I might not have been surprised ... jumbo frame support, for example, is notably absent from the TEG-S80TXE spec sheet. On the other hand, the TEG-S8 only offered an 8 KByte data buffer; that in the TEG-S80TXE is 128 KBytes in size.

Whereas the TEG-S8 was based on a head sink-augmented Broadcom's BCM5398, the TEG-S80TXE "brains" take the form of a Vitesse (now Microsemi) SparX-G8 VSC7388, which dates from late 2004:

Click to enlarge.

It's no longer listed on Microsemi's product portfolio page, but a Google search still enables regurgitation of a datasheet from other sources. The LAN transformers are also different this time around; from Tonyo (strictly speaking, Bi-Tek Tonyo), versus Dongguan Mentech Optical & Magnetic. No, I have no idea why this design went with three dual and two single transformers, versus four duals.

Flipping the PCB over, as usual for these kinds of highly integrated consumer products, produces a bare-save-for-passives-and-solder-points result:

So what happened to the TEG-S80TXE? The symptoms of its demise were similar to those of the similarly geriatric TEG-S8 and D-Link DGS-1005D; a still-illuminated power LED, with all others extinguished. While a failing "wall wart" might be a possibility, my past acquisitions of replacement power supplies for prior failing switches produced unsuccessful-resurrection results.

Instead, I'm again suspecting a failing capacitor or other component that rendered the switch's single-chip controller dead.

Also see:

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