Disassembling a “dumb phone”

May 16, 2023

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Flip phones and other “dumb phone” form factors are apparently “hot” with Gen Zers (and others) at the moment, so says mainstream media. There’s even a subreddit devoted to them. So too, apparently, are decades-old digital cameras (such as these beauties)…but that’s a topic to delve into more detail another day…

What’s a “dumb phone”, you say? Per the relevant Reddit wiki:

A “dumb phone” is a cellular phone with less or no “smart” features as a smart phone. It’s actually called a “feature phone” but it’s commonly referred to as a dumb phone because it’s seen as the opposite of a smart phone.

Dumb phones lack the advanced technology of smart phones and typically only have core tools like calling, text messaging, maybe a calendar or notes, and typically do without feature-rich apps like social media and maps.

One of my neighbors, who knows that I periodically donate mobile phones, computers and the like to local charities, brought over the other day a flip phone which had been collecting dust at her residence for a few years. It was a LG 442BG, a circa-2016 TracFone Wireless (a US prepaid cellular service provider)-tailored (i.e., carrier-locked) variant of the LG 440G shown here:

Glancing at it, I suggested that it probably wouldn’t be usable to a donation recipient since (due to its age) it likely relied on a 3G (or older) cellular network that the major carriers had already phased out. But, I told her, if my hunch was right, I’d welcome the opportunity to instead do a teardown on it for EDN. She agreed with my proposal, and I promised I’d do definitive research on the flip phone before putting it “under the knife”.

The situation was, it turns out, even more dire for the LG 442BG than I initially imagined. Not only was the flip phone 3G cellular network-based, but it was also GSM-based. I emphasize this point because, it turns out, CDMA-friendly (and GSM-unfriendly) Verizon had acquired TracFone Wireless in November 2021. Teardown it is, then!

I’ll begin with the obligatory set of outer box shots:

Look at the coverage map graphic at the top. See, I told you…GSM.

Uniquely identifying information greyed out for my neighbor’s privacy protection…

Opening the front flap:

provides us with even more overview information on the left side:

and the first glimpse of our patient on the right side:

Here it is out of the cardboard box, but still in its clear plastic sarcophagus, as usual, alongside a 0.75″ (19.1 mm) diameter U.S. penny for size comparison purposes (the phone’s un-flipped size is 3.85″ x 2.00″ x 0.73″, and its weight including the battery is 3.63 ounces):

Turn the sarcophagus around and you’ll encounter…a jumbled mess (in fairness to my neighbor, the result of its past use and subsequent re-storage):

The literature packet (along with a mysterious dark-color rectangular non-magnetic thing with a white backside sticker that I didn’t remove; I’m not sure what it’s for, and it doesn’t seem to be mentioned in the user manual) slides right out the top:

To get at the rest, I needed to crack open the sarcophagus (hey, I wonder if the mysterious rectangular thing was a shield for placement behind the RFID tag?):

Prepaid service card details again obscured for neighbor privacy:

and, of course, obligatory closeup shots of the “wall wart” specs and micro-USB connector:

Now for our patient. Front (folded-up) view first, of the mini-display and 1.3 Mpixel camera:

Right side (I think that hole toward the top of the phone was for an optional wrist “leash”, although I see no indication that one was actually ever included with the phone):

Left side (to the left/top of the phone is the up/down volume toggle, with the charger power input to it right/toward the bottom):

And (boring) back:

Finally, the hinged top:

And (again, boring) bottom:

Flip the phone open and the first thing you’ll likely notice is a sticker affixed to the keyboard with power on/off instructions. Apparently, my neighbor didn’t use the phone much (if at all)!

Speaking of phone usage (and fundamental operation), before beginning the teardown, I thought I’d see if it was still in working condition, including its charging capabilities:

and boot-up abilities:

That’s a big “yes” on both fronts, folks!

The battery compartment (if it exists) is often a fruitful first bet when figuring out how to get a device apart, so that’s where I focused my initial attention and efforts:

Look at the upper left corner of the phone, previously underneath the back battery cover, and you’ll see a small vertical plastic pin. The chassis cavity in which it’s located is also accessible by the previously mentioned hole at the top of the right side (when viewed from the front) of the phone.

Remember my earlier missing “wrist leash” (aka, “strap” or “lanyard”) comment? My theory is that the thin-thread end of the leash goes through the hole and loops around the pin. Here’s a visual example of what I’m talking about:

Enough of the asides…let’s get that battery outta there:

Specs and such are clearly visible:

as is the now-uncovered full-size SIM (remember folks, this phone dates from 2016).

Let’s remove that too (numerical code on SIM once again greyed out for phone-donor privacy):

You may have already noticed the six screws exposed on the backside after I removed the battery cover: one in each corner, and one midway on each side. Guess what’s next?

Another quick aside: going forward, I’m going to refer to this half of the phone-when-flipped-open, containing the keypad, microphone, battery, SIM and presumably also the primary PCB, as the “body”, and the other half, containing the displays, the camera and speaker, as the “flip”. After removing the six screws holding them together, the two halves of the body case separated fairly easily, although there were still plenty of plastic clips to…unclip…

Let’s first look more closely at the inside of the back half of the body:

In the upper right is the haptic (aka, vibration) motor, whose electrical contacts press-connect against the PCB (if you look closely at the one-earlier two-halves photo, you can see exactly where). To its left is a metal-and-foam assembly which, I believe, serves only a mechanical purpose: to hold the rectangular connector connected to the PCB (again, reference the earlier photo) in place. And between and above them, what’s that stamped into the plastic? “LG440G”? But I thought this was the “LG442BG” ;-). A firmware-based cellular carrier “lock” in the latter case, I suspect, is the sole difference between them. Finally, note the two flexible “pins” in the lower right, which are seemingly connected to a thin metal assemblage below and extending to either side of them, and which also press-connect to contacts on the PCB. Read on for my theories as to what this is.

Now let’s look at the insides of the other half of the body:

There’s not a lot that we haven’t already seen, thanks to the voluminous battery cavity, and/or already mentioned by press-connect association. The battery contacts at upper left are now fully visible, and what’s that down at the bottom of the phone? It’s the electret microphone (again, folks, this is a 2016 design)!

Next step: detach that flex PCB-terminating connector.

And with it disconnected, we can now pop the PCB right out:

Comparatively boring (aside from our first glimpse at the “action-packed” portion of the electret microphone) PCB frontside first:

whose array of switches mate up with the backsides of the phone’s keypad buttons (note, again, the “LG400G” reference):

Now for the “action-packed” backside.

The Faraday cage popped right off:

leaving me momentarily delusional that I might be able to subsequently reassemble the phone in mechanically intact and fully functional form.

Faraday Cage closeups first:

And now, what you’re all really interested in:

In the upper left corner are two chips I can’t ID, although their proximity to the battery contacts has me suspecting they’ve got something to do with battery charging and/or system power generation (reader insight is as always welcomed). The larger, lighter one to the left has the following markings:

001A
F627
2RP

while the slightly smaller and slightly darker sibling to its right is adorned with the following faint topside stamp (discerned to the best of my old, tired eyes’ abilities):

TI66AFYZI
TRA2058D3

The IC in the upper right corner is easier to ID; it’s Broadcom’s BCM2070 Bluetooth 2.1 + EDR (enhanced data rate) single-chip baseband processor and 2.4-GHz transceiver. No Wi-Fi support to be found anywhere; did I mention that this is a 2016-era design? And where’s the Bluetooth antenna? I can’t discern a PCB-embedded one, which is the common approach nowadays. Instead, I suspect it’s that bottom-of-phone, two-pin-fed assemblage I mentioned earlier.

In the next “row” is, at left, a Fidelix multi-chip module marked FMN2SD1SBK-50IA and containing, this handy online guide tells me:

2 Gbits of NAND flash memory with a x16 system interface and
1 Gbit of 200 MHz DDR SDRAM, again x16,

with both memories running at 1.8V and operating across a -40°C to 85°C temperature range. Below it is the larger Qualcomm QSC6270 single-chip HSDPA/WCDMA and GSM/GPRS/EDGE single-chip controller, integrating (among other things) a radio transceiver, baseband modem and multimedia processor, along with power management functionality. Although Qualcomm is mostly known for its CDMA “chops”, it clearly also was a supplier “player” in the GSM realm.

To the right of the Fidelix-plus-Qualcomm IC cluster, and to the left of the micro-USB connector, is another IC I can’t seem to ID, marked:

17 3F
D2M

Ideas, anyone? Also note, BTW, the two volume-control switches above the micro-USB port.

Finally, the bottom row. Left-to-right, there’s first a two-Avago (previously Agilent, before that HP, now Broadcom…phew!) chip clique, both wireless power amplifiers, an A5502 for UMTS Band 2, and an A5505 for Band 5. In the middle is another “mystery IC” with these markings:

SP1
QJC65

And at right is an RF Micro Devices RF3194 quad-band GSM power amp module (with a way-cool wireless-themed logo in one corner).

I “could” have stopped here, and maybe even gotten the phone back together in one piece (with no extra pieces) and fully functional to boot (both figuratively and literally). But that flex PCB dangling from the “flip” case taunted me; I really wanted to see what was on the other end of it, specifically that awe-inspiring 1.3 Mpixel camera (I jest). So, I pressed on. See the screw holding a metal piece in place in the upper left corner next to the aforementioned “leash” pin?

Let’s remove ‘em both:

This step admittedly didn’t seem to do much, at least as far as getting inside the “flip” was concerned, although I suspect that the bracket’s tension in its original location had acted to hold the hinge in place (keep reading for more on this). In the midst of the removal process however, I inadvertently dislodged the keypad from its mooring:

Along with the rubber piece on the side that activated the volume switches:

Initial attempts to separate the two halves of the flip via the seam between them were spectacularly unsuccessful; something other than just plastic tabs was holding them together:

In search of screws, I first turned my attention to the plastic piece on the front that surrounded (and protected) the LCD along with encircling the camera:

I got it most of the way off before it began to crack (a preparatory heat gun exposure to loosen the adhesive would have, in retrospect, been wise):

After all that, I found no screws underneath…

…although before proceeding, here’s a closer peek at that camera…

Next, I thought I’d tackle the hinge. I was pleasantly surprised to find that it (and the flip connected to it) now popped off the body fairly easily. One end was spring-loaded:

and the other, I suspect, had been normally held in place by that mysterious metal piece I’d earlier removed:

Here are some more shots of both the hinge (including that flex PCB that continued to taunt me) and the housing that both ends fit into.

Unfortunately, that exercise didn’t get me inside any further (via the seam segment on that end) either:

A bit frustrated, I put the flip aside for a bit, a short-term break which, from past experience, I suspected would be long-term productive. Indeed, it was. When I returned to it, I noticed two round indent suspects in the bottom corners of the large LCD, which I’d bet at least some of you already noted in previous pictures, and which, when I (“enthusiastically”, I admit) popped them off, revealed screw heads underneath:

Progress, finally, but only partially; the case’s other end was still being somehow held together:

In search of what I suspected were two more screws, I peeled off the protective plastic from the other side of the flip:

A-ha!

With the remaining screws removed, the two halves of the flip case finally (easily) separated:

Looks from the inside stamp that LG reused the outer flip case piece from the B460 flip phone:

We now can see where the flex PCB ends up: at a PCB-based connector where its signals subdivide to control the camera module as well as to drive both of the flip’s displays (the smaller outer one is shown here). Also note the metal assembly surrounding the PCB, which (I’m guessing) holds it in place and protects it, as well as providing additional rigidity to the entire flip assembly. Also note the speaker at bottom.

In order to contemplate the larger inner LCD more completely visually:

it’s necessary to first lift the internals out of the flip case surroundings, thankfully an easily accomplished task.

Here’s the flip case shell, now absent its contents:

An overview picture of the new-unobscured large-LCD circuitry side (I have no idea whose finger- and palm-prints are all over that screen ):

and small-LCD circuitry side:

In closing, here are some closeups of the small LCD itself:

the camera assembly above it (I’m guessing that what’s in between the sensor-and-lens assembly and the merged-signals connector I mentioned earlier is an ISP chip):

and the speaker:

And that’s all he wrote (nearly 2,700 words in…yikes!). While I conceptually miss flips, “candy bars” and other highly pocketable form factors, all I need to do is briefly ponder how much comparative time I spend doing various data-centric things on my smartphones versus…y’know…making and taking voice calls…to acquiesce that a large-screen (but still pocketable) form factor is more feasible, practically speaking, for me. What about you? Let me know your thoughts on this, and/or anything I’ve covered in this teardown, in the comments.

—Brian Dipert is the Editor-in-Chief of the Edge AI and Vision Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the company’s online newsletter.

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