TP-Link MC220L: Media conversion keeps the network well

Got lightning? A bidirectional RJ45/SFP intermediary can, by “taking one for the team”, keep it from propagating through the remainder of your network.

Back in November 2024, I detailed my initial attempts (with underwhelming results) to figure out some way to avoid using the two lightning-prone spans of Ethernet cable running around outside my house (which I’d inherited when I bought the place, mind you; the bad idea wasn’t mine in the first place!) and without replacing them with expensive- and complicated-to-install alternative cable runs inside the house. And speaking of lightning, we’re nearing the start of Monsoon Season 2026 as I write these words in mid-May…

…but I won’t be gritting my teeth quite so intensely this year, thanks to reader Steve Strobel:

You don’t need fiber from your ISP to protect 99% of your equipment from surges on their connection. After their modem/router, you can convert to fiber, back to Ethernet, then go to the rest of your network. A pair of gigabit Ethernet/fiber media converters (for example, TP-Link MC220L, about $21 each) and a foot of fiber should do the job. Or if your switch has a SFP port, drop an SFP fiber transceiver in that and you need only one converter.

Here’s my response:

You are brilliant! What I’ve just realized thanks to your comments is that if I put a pair of these at each of the endpoints of each of the two external Ethernet spans (eight media converters total), along with four short spans of SFP cable (one per endpoint, spanning each pair of media converters), I can electrically isolate the Ethernet switches (and wired LAN clients connected to them) at each endpoint from any lightning-induced EMI that the external Ethernet spans might pick up. And all for ~$250 total. Thank you! Off to order now…

Transceiver sacrifice

And that’s exactly what I did, initially alluded to in the comments of a teardown (of one of the devices that died in the October 2024 lightning debacle) published the following May. I promised a teardown back then, and although it took me a bit longer than planned to actualize that particular aspiration, you’ll be getting one today.

First off, here’s what one of the four paired TP-Link MC220L Gigabit SFP Media Converter clusters looks like in action, in my furnace room.

One of the only-slightly-quirky devices is Ethernet-fed by the eight-port GbE switch (not shown) next to it. The other one connects to the Ethernet cable that then heads outside and around the west and north sides of the house, where it re-enters at the master bedroom. There’s another two-device cluster there, of course. Two more clusters handle the Ethernet span running between the west and east sides of the house. And interconnecting each two-device cluster is a 0.3 meter strand of SFP fiber optic cable (or so I thought at the time…keep reading).

All nine devices (including a spare) were factory-refurbished, came with multi-year warranties, and cost me less than $20 each (four of them less than $15 each) on eBay. And the cable four-pack from Amazon cost me less than $28. This isn’t a foolproof fix, mind you, but it’s a cost-effective workaround. Even if I need to replace all four external-facing transceivers each time, there’s a monsoon “event”. It’s less than $100 out of pocket (not to mention only a five-minute replacement job), a much less costly outlay than when multiple much more expensive LAN gadgets had gotten fried. In practical preparation, in fact, I’ve already bought six more spares, this time from StarTech (and sourced from Woot) and setting me back only $5 each:

Add fiber to your packet diet

Enough of the background chatter; let’s get to tearing down. The device you’ll be looking at today is not one of the nine TP-Link devices I’ve already mentioned. Nor is it one of the six StarTech ones. It’s a tenth TP-Link MC220L, again from eBay, but this time used and missing a power supply (but still functional? Dunno). I’ll start with a stock shot.

And now some photos of our actual patient, as usual accompanied by a 0.75″ (19.1 mm) diameter U.S. penny for size comparison purposes.

Used, like I said!

No wireless capabilities, thus a rare teardown device absent an FCC certification ID on the label.

Now for the sides (in clockwise order):

Before proceeding further, I grabbed the wall wart and paperwork (PDF) from the spare functional unit, to share some photos of them with you, too.

Protocol conversion here: media conversion elsewhere

I anticipated that getting inside would be relatively straightforward, and I wasn’t disappointed. You probably already noticed the four total screw heads, two each on two of the sides. You know what comes next, right?

And…open sesame:

Two more screws to go:

And the PCB is free:

The design is quite simple; the notable topside contents include a Realtek RTL8367S layer-2 managed 5+2-port 10/100/1000M switch controller and a Group-Tek HST-2027DAR (PDF) dual-port 10/100 BASE-T Ethernet isolation transformer module.

I was initially baffled as to where the optical/wired bidirectional conversion circuitry was located, until I realized that it was at both ends of the cable itself. Unfortunately, I don’t have a spare available to dissect, so you and I will both need to satisfy ourselves with others’ analyses, such as this one, which showcases a module based on an Atheros (now Qualcomm Atheros) AR8033 Ethernet transceiver and two SwapNet NS681679 LAN transformer modules.

And on the other side of the PCB? Nothing but solder points and embedded traces:

I’ll wrap up with a set of side shots:

and turn it over to you for your thoughts in the comments!

Coda

Subsequent to doing the teardown and writing the previous prose, I revisited the SFP cable page at Amazon’s website to purchase another cable for future module teardown purposes and first-time noticed the word “Copper” in the product title. With no shortage of embarrassment, I must admit that the whole time I’d had the media converters active in my network to that point, they’d not been providing any meaningful degree of galvanic isolation after all. I quickly sourced true fiber interconnect, 0.5 meter multimode active optical cables (AOC) to be exact:

and installed them in place of the direct-attach copper (DAC) predecessors I’d been naïvely using up to that point. Although, in my slight defense, I had long been wondering why they’d been so inexpensive. The AOCs, which weren’t that much pricier especially in the ultra-short lengths I needed, work great.

Although in a final twist to this tale, I subsequently learned that (strictly speaking, at least) they shouldn’t be working—at all, actually—since the media converters are SFP-lineage but the cables (and their endpoint transceiver modules) implement the successor SFP+ standard.

That SFP (port)-vs-SFP+ (module) protocol incompatibility exists in contrast to the physical compatibility between SFP and SFP+ connectors and modules is mind-blowing to me. I’m guessing that this mismatch has also caused no shortage of headaches for multi-generation SFP technology suppliers and implementers alike, and that vendors have in response come up with above-and-beyond-the-spec workarounds that support full backwards-compatibility such as the one I thankfully experienced.

I’ll save further discussion for a near-future planned dedicated post on the topic, but felt it was important to do an initial fess-up here.

—Brian Dipert is the associate editor, as well as a contributing editor, at EDN.

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