Teardown: Router hardware provides flexibility

-July 06, 2017

In a recent teardown, I told you about On Networks' N150R, a basic 802.11n-class router that performed much better once its vendor-supplied firmware was swapped out for that of a NETGEAR-branded hardware twin. This time, I'll be telling a conceptually similar story, but involving a mainstream 802.11ac-class product, the ZyXEL X650. This now-discontinued router is AC1200-rated, translating into 867 Mbps peak speed for 802.11ac (5 GHz) and 300 Mbps for 802.11n (2.4 GHz). I got it for free bundled with a SiliconDust HDHomeRun Prime network tuner (which, as regular readers already may recall, I regularly need to re-purchase). At around the same time, it was selling for $34.99 standalone.

Before I discuss its transformation potential, let's dive into the dissection. Here's a set of box shots, to start:

Inside the box, there's a slim quick-start guide, along with a documentation-and-utility CD:

A wall wart power supply:

And, of course, the router itself:

Note the abundance of passive airflow (no fan inside) vents along both the top and sides:

Here's a closeup of the bottom-side label:

And speaking of closeups, in the left corner of the router's backside is a rare and curious sight: a physical switch to disable the router's dual-band Wi-Fi radio subsystem:

Remove the four rubber underside "feet":

And underneath each you'll find a Philips head screw:

Remove each of them, gently pry away a few plastic tabs and the top half of the plastic chassis pops right off:

That exposes the topside of the PCB:

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Immediately apparent to your eye, perhaps, are the three Magnetic Communications Corporation (Magcom) transformers at the top, one GT1802DA and two 3603DAs, respectively servicing the WAN and four LAN Ethernet ports above them. Or you might have first noticed the two large heat spreader-obscured ICs on the PCB. Or the mysterious unpopulated IC footprint in the bottom right corner, with two unpopulated connector sites below it. On those last points, hold your thoughts for a bit.

The XyXEL X650, from what I can tell, appears to be based on Realtek's RTL8197D-11AC reference design, and the two external antennas are each dual-band in nature (note the discrete black and grey wires routing to each of them). Looking first at the top right corner of the PCB, you'll see an Edimax EW-7822MAC add-in board installed in the main PCB's mini PCIe expansion slot:

The primary IC on it is a Realtek RTL8812AR, which forms the heart of the router's 5 GHz Wi-Fi subsystem:

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Its Wi-Fi companion, the Realtek RTL8192CE, is soldered directly to the main PCB, to the bottom left of the mini PCIe add-on board, and does 2.4 GHz duties:

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So what's the deal with the unpopulated IC socket to its right, accompanied by all sorts of "D"-prefix component markings on the PCB?

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And why did the router hardware manufacturer bother including a seemingly redundant mini PCIe add-on socket (and add-on card for it) in the design? I can't say for sure, but I have a theory. Recall again that the ZyXEL X850 is an "AC1200"-class router; this means that it implements 2×2 MIMO in both the 2.4 and 5 GHz bands. If the manufacturer wanted that same PCB to alternatively support 1×1 MIMO (i.e for a single-stream-per-band AC580-class 802.11ac router, or a similarly elementary 802.11n product), it could dispense with the add-in card, alternatively populate the additional IC site on the main PCB, and devote one antenna (and main PCB cable connector) each to 2.4 GHz and 5 GHz operation.

And what about those two unpopulated connector sites below it (and to the right of the array of LEDs)? I didn't bother taking a close-up photo, so you'll have to trust me when I tell you that the associated PCB markings reveal that they're intended for USB capabilities such as locally tethered network printers and storage devices. The router's primary SoC supports these functions, so their omission likely just reflects the router vendor's desire to reserve these features for a higher-priced router model, implementation-differentiating between them solely via software (along with connector inclusion and enclosure exposure to it/them, of course).

Speaking of the router's primary SoC, WikiDevi tells me that it's the Realtek RTL8197D, and that it's found under this particular heat spreader:

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To its lower left is the system's DDR2 SDRAM, a Nanya NT5TU32M16DG 512 Mbit memory device. And underneath the other heat spreader, supposedly, is a Realtek RTL8367R-VB IC implementing GbE switch functions (I've left the heat spreaders, therefore router functionality, intact so that I can later put it together and donate it):

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Remove four more screws and the PCB easily pulls away from the enclosure; you can then flip the board around to bring the as-usual comparatively bare backside into view:

Here's a close-up of the more meaningful bits, showcasing (among other things) the Macronix MX25L3206E 4 MByte serial interface flash memory found there:

And now we can finally get to the "hardware twin" aspect of the story alluded to in the introduction. Remember how earlier I identified the mini PCIe add-on board as being Edimax-branded? Well, as it turns out, the ZxXEL X650 is essentially hardware-identical to the Edimax BR-6478AC router, which is a pretty well-reviewed product to boot (and does implement a USB port, by the way).

Why does this matter? ZyXEL hasn't released a firmware update for the X650 since mid-2013, and many of the product reviews therefore reflect a "great hardware potential, but buggy and incomplete software" status for it. But Edimax has done a better job of delivering long-term software support for its X650 equivalent, the BR-6478AC. And enterprising X650 owners have figured out how to shoehorn Edimax firmware updates onto the ZyXEL-branded router, transforming it into a more robust product in the process. Just don't try to use the nonexistent USB port that the Edimax firmware swears should be there!

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