#0008: Repair and Analysis of USB Micro type-B cables

If you are anything like me you probably have a sizeable collection of broken Micro USB cables neatly spooled onto a hook, or into a bag. Alternatively, you may even have them tangled into a rat king in a box or drawer somewhere … that is if you are a barbarian. You know who you are. So in an effort to lighten my ‘Spares & Repairs’ bin short of throwing things away (perish the thought!). I though it’d be good to repair a few. I know crazy right?

How and where do Micro USB cables typically break?

In order to repair something, we must first asses the damage. Where is it and how much is there? Well, with regards to the generic male USB 2.0 type-A plug to male USB Micro type-B plug cable: the damage is predominantly focused in the male Micro USB plug. Please note I will be using the term ‘Micro USB plug’ as shorthand for ‘male USB Micro type-B plug’ throughout this article.

Initially, I used to get annoyed whenever a cable broke and rebuke the relatively delicate Micro USB plug as poorly designed. However, on reflection it is actually rather good that the weakest point in the pairing of the plug and socket: is in the plug and not the socket. Especially since after such incidents, the device socket tends to end up with little if no damage at all.

This is assuming that the majority of accidental breakages happen under certain conditions. These include: firstly, that the Micro USB plug is inserted into it’s respective socket on the device at the time. Whereupon it comes into acute mechanical stress by something akin a sudden impact (e.g. from a fall); or by a particularly vicious cable snag. This stress consequentially puts a lot of pressure on the connection between cable and device. Which in most cases causes the cable’s plug to give in before the device’s socket. Sometimes both are damaged if the impact is strong enough. However in a more typical scenario the plug breaks first, and in such a way as to leave the socket relatively unharmed.

Although my knee-jerk reaction is irritation whenever I perceive something as genuinely designed to break; I think in hindsight it is better that the cable’s plug is designed to break before the device’s socket. Since the cable is far easier (and consequently cheaper) to either replace or repair than the device would be. After doing some research, it seems that this is a conscious design decision (citation needed) and not one based on anti-consumer avarice, which (as a long time purchaser of consumer grade electronics) is the assumption that I have been conditioned to have in these types of scenarios. “Think Different”, Think Planned Obsolescence.

In this case, it is actually an iterative improvement on it’s predecessor: the Mini USB standard. Which suffered from port damage due to the shape and structural strength of the male plug, coupled with the fact that the retention and locking mechanism is located within the socket in the Mini USB standard. Whereas within the Micro USB standard, all such fragile and consequently breakable parts are located cable side. Having said that though, it still sucks when useful tools break so let’s try fixing them.

Structure of a male USB Micro type-B to male USB 2.0 type-A cable.

The male USB Micro type-B (or Micro USB) plug on average has typically four or five pads at it’s cable side and five interface pins that mate with it’s counterpart female socket. Please refer to the pin out diagram.

USB type-A:
Pin | Name | Wire Colour | Function
1 | VBUS | red | +5 volts supply
2 | D- | white | Data-
3 | D+ | green | Data+
4 | GND | black | Ground

USB Micro type-B:
Pin | Name | Wire Colour | Function
1 | VBUS | red | +5 volts supply
2 | D- | white | Data-
3 | D+ | green | Data+
4 | ID | no wire | ID pin for OTG functionality
5 | GND | black | Ground

Its simple really, pins 1 and 5 are used for power. Pin 1 supplies the +5 volts and pin 5 is it’s ground. Pins 2 and 3 are used for transmitting the data signals for communication. And finally, pin 4 is an identification pin, which is used for USB ‘On The Go’ functionality. It essentially tells the device that it is connected to, whether or not it is to act as a host system or a slave device when communicating with the device on the other end of the cable.

hyperlink: post_#0009:_Brief_guide_to_creating_a_USB_OTG_cable

Its a very similar setup with the male USB 2.0 type-A plug on the other side of this cable, except that it lacks an ID pin. Pin 1 is the V bus carrying +5 volts, pin 4 is the signal ground, and pins 2 and 3 are the negative and positive data pins respectively.

The reason the USB type-A plug lacks an ID pin is because any device that has a full sized female USB type-A port is already assumed to be the host system. Finding a peripheral device such as a keyboard (with the exception of USB pass-through), or mouse, or even a smart phone with a full sized female USB type-A socket is non-standard; as are the male USB type-A to male USB type-A cables needed for them.

The wikipedia.org article (“USB hardware”) mentioning this cable labels it as ‘proprietary, hazardous’. If I were to guess as to why that is, I’d say its because it allows the connection of two host systems (e.g. 2 personal computers), with no protocol to decide the role either system has to play. Additionally the input of power into a host system via it’s USB ports may cause damage (e.g. to it’s USB controller) because it may lack short circuit or input protection.

The Repair

Now that we have a basic understanding of the structure of the Micro USB plug and where the damage typically is. We can proceed to repair one.

Recommended tooling:

• soldering iron
• hot air station / heat-gun / lighter
• hot-glue gun
• precision knife
• third hand clamps (handy grips, etc.)
• testing adapters
• female USB type-A socket breakout board
• female micro USB type-B socket breakout board
• multimeter
• pliers

Consumables:

• hot-glue
• heat-shrink
• Micro USB male plug kit
• (lead-free or leaded) solder
• rosin flux
• electrical tape

P.P.E.:

• safety glasses
• light heat resistant gloves

The list above is just as a guide the the types of tools and consumables that you may need. Most of them are optional and are subject to personal preferences and circumstance.

Methods of repairing items

Most real world cable repairs I think broadly fall into one of the three categories or ‘methods’ I outline below. They all have advantages and disadvantages. Some allow for saving more time than money and other’s vice versa. Which ones are most appropriate to use will predominantly be based on the repair technician’s personal preference, available materials, and circumstances.

For example one could if one had two good candidate cables, splice them together into a working unit (i.e. method #1) using minimal tooling: just a knife to strip the wires, several unsoldered pig tail splices for the connections, and some electrical tape to isolate the USB wires from each other. And it would work fine. How long for? Who knows – but it will work for the moment and that may actually be enough. I give the example just to illustrate that things can be repaired a number of ways depending on either the person’s (in this case low) resources, and preferences; which can the run the gambit from the “just get it working for now” repair (shown above), to the perfectionist who wants a permanent repair that will outlast the product.

Method #1: splice two cables together

Probably the quickest method of repair involves simply splicing together two cables. This involves cutting the damaged parts off, then joining and soldering the four pairs of wires together according to their colouring. Red and red, green and green, white and white, black and black; and even sometimes the foil metal shielding if present. Simple. However, be mindful to first electrically isolate each of the four individual pairs, then cover over with a larger gauge heat shrink (for neatness) or electrical tape (for cheapness) to group everything together. I recommend a soldered Western Union splice as a method of joining the wires in the pairings. This is due to it’s relatively low profile and due to the mechanical strength of the resulting connection. Which means that in the case of any future tension on the cable such a sudden hard snag; chances are good that the new connection will not break. Nothing hurts my pride quite like having to repair one of my prior repairs. Consequently, I tend to do it properly the first time round.

hyperlink: post_#0003_Basic_techniques_for_connecting_wires

Now, there are obvious limitations to this method. The most pressing is that cables tend to get damaged in the same spot as each other. Especially when used in the same environment (or by the same people!), and in the same applications. So this method is not applicable in these cases. However in cases where it is applicable it is the shortest and easiest route to creating a reliable and viable cable. Primarily because it effectively bypasses the often finicky business of repairing the actual Micro USB plug.

Method #2: mend and make do (with salvaged spares)

So, like I mentioned above: most of these cables break at the same point. Namely, the male Micro USB plug. So unless you want to end up with a bunch of double ended (full size) male USB type-A cables. Splicing together the good ends of your broken cables isn’t going to do you much good.

So what now? Well first things first. We need to understand the extent of the damage itself. When you examine a broken Micro USB plug. If the metal outer shielding of the plug is present, then chances are that the metal plug itself is bent out of alignment by a fair few degrees across it’s broader sides. In this configuration, the state of the plug’s internal pins is unknown; or more to the point: it is unknown as to whether there is continuity across the pins (i.e. are they snapped or broken). By using a pair of pliers you can carefully correct the angle of the plug. I recommend doing this slowly before trying any other fixes. It needs to be slow, in order to give the delicate internal pins time to bend back into alignment. If the cable works after this, then that means that the internal pins were merely bent and not broken; and it also means that the repair is effectively done.

Alternatively, if after angle correction there is no continuity across the cable. Either by buzzing it out using various adapters and a multimeter — or just by plugging it into (hopefully inexpensive) devices and seeing if the devices recognise each other. Then it is time for a more invasive solution. I stipulate ‘inexpensive’ because many devices with USB ports don’t have adequate protection in cases of hard shorts to ground. It’d be pretty disheartening if a person, for example killed that USB 3.0 port on a their wiz bang gaming rig, because the wires were accidentally soldered incorrectly or shorted on that cheap shit cable they were trying to mend. I doubt that would actually happen, but better safe than sorry.

With a sharp knife, slice into the rubber or plastic sides of the plug. Create a broad slice from where the metal Micro USB plug’s base is (or was), all the way across the plug housing and up close to the strain relief. Peel back the rubber or carefully pry open the plastic to reveal the base of the Micro USB plug. Here you should be able to see where the four wires (for a data cable) or two wires (for a power cable) connect to the Micro USB plug’s base internal section.

This area of the cable: where cable meets Micro USB plug; tends to be either injection moulded with plastic or rubber, or filled with a type of hot glue. It is very easy to do more damage to the plug trying to get to it, then the damage that caused the cable to become inoperable in the first place. So if you intend to repair the Micro USB plug (rather than replace it), I advise proceeding with caution here.

Once you have made it to the base of the Micro USB plug. You many notice that the metal outer shield of the Micro USB is sometimes removable. If yours is, then it should be held in by a clip of some sort. Unclip it. Continue carefully dissembling the plug until you find the fault. In my case the internal pins broke as the plug was bent. I could try to re-solder them together or I could replace the Micro USB base with one from either another plug or a spares kit. Since this is the ‘mend and make do’ method, let’s say I went through the tedium of realigning the tiny pins and soldering them – and without melting their plastic housing or shorting them together no less … What I actually did was just replace the plug base with a known good one, for time and reliability.

Reassemble the plug. Then fill in any cavities you may have carved out on your way in, with hot glue. Close the cable head up, then wrap it in electrical tape. Done.

The strength of this method is that you can repair the cable without necessarily having to purchase additional parts. However the disadvantages are that it is very time consuming and finicky work. Work that could ultimately leave you with a plug that is structurally even weaker than the one you started with. So it may soon break again if not handled with care going forwards.

Make sure to do a through continuity test before pressing this cable back into service. Especially when it comes to testing for shorts across the pins. This includes pin 4, which depending on the testing adapter socket you are using, might be inaccessible. In this case I used to use crocodile-clip leads and needles as probes to test the pins on the exposed male plug without a female adapter. Although, I actually recommend just purchasing (or creating) a female Micro USB socket breakout board. It makes life so much easier than faffing about with a bunch of random low quality adapters or needles … which is what I used to do, and don’t really recommend. But sometimes you have to just use the tools in front of you.

Method #3: use a spares kit

This is probably the simplest actual repair after splicing two appropriate cables together. This method involves using a kit to replace the entire Micro USB plug assembly, including the strain relief. After cutting off and discarding the Micro USB head, remove the outer insulation of the cable, strip the the USB wires within and tin them. If the outer insulation is a fabric braid type, then melt the tip of the insulation with heat to stop it from unravelling.

Next up, slide on heat shrink (for cable bend relief), and then the Micro USB plug housing. This stage is probably easiest to forget. I can’t count the number of times, I have made a really nice soldered connection, only to undo it because I didn’t remember to slide on heat shrink beforehand. It’s funny, it only really happens on the more permanent joints, like the Western Union splice. I think its because I tend to be too preoccupied with making a good strong connection, that consequently: these types of things tend to slip my mind at the time. So take your time and do things methodically.

Just as an aside: heat shrink, in my opinion makes a good form of bend relief for a cable because it makes the cable a little stiffer along the length leading into the plug. This gives it resistance to bending to extreme angles, or allowing repetitive bend or flex damage to concentrate on a singular point on the cable. As for strain relief for the solder joints on the plug base: adding heat shrink to the cable does little. Id est it doesn’t prevent tugging force on the cable from exerting strain on the soldered connections between the cable’s wires and the Micro USB base’s pads. I’d carefully tie the cable end into a loose overhand knot (if it is of a thin enough gauge to do this), making sure not to cause any acute stress points in the wires as a result. This knot will act as a stopper against the insides of the Micro USB plug’s plastic housing. I am not sure whether or not this is generally advisable protocol, I am just stating what I tend to do. The loose knot offers some resistance to a tugging force as it tightens against the hole in the plastic housing. This in turn relieves the solder joints of some of the strain. Alternatively, filling the Micro USB plug’s housing with hot glue will also act as a decent form of (tugging) strain relief for the solder joints. These two methods do this by redirecting the pulling force away from the solder joints and into the housing and general superstructure of the plug.

Moving on. Now with everything in place, solder the USB wires to their respective pads on the Micro USB plug base. This includes the cable’s outer conductive shielding if present. In order to know which pads correspond to which pins: refer to any user guides or datasheets that may have been shipped with your spares kit. Alternatively test the continuity of the pads to the pins using a multimeter and a female Micro USB breakout board.

To connect the cable’s shielding: roll the loose strands into a cord. You may need to wrap this cord with another wire to extend it enough to reach the Micro USB plug’s outer metal housing. Which is a little further away than the USB solder pads on the example kit I have. I needed this extension to the shielding cord because when I cut the cable, it made all the internal wires and strands equal in length, so an extension was necessary in my case. After scratching off the finish on the part of the Micro USB plug’s metal housing that you intend to solder onto. Apply a small patch of electrical tape to insulate the USB wires from the shielding connection. Next, solder the shielding cord to the metal housing. You may need to apply solder to the twisted shielding cord to harden it and fuse the extension if necessary.

Now. Isolate the internal USB wires from each other, by injecting hot glue over and between the four wires. I use the electrical tape from before as a backing for this. I chose to have the adhesive side facing the USB wires, because I intended to wrap it around them at this stage. After this, pull the heat shrink into position then apply heat. Pull the plastic housing over the plug base and align the plug so that it is straight. I used the plastic cap to set the plug’s position. Once satisfied with the plug’s position within it’s plastic enclosure; remove the plastic alignment cap again and inject hot glue to fill any cavities between the plug base and the enclosure. Reapply the alignment cap. Then carefully apply some heat to the now closed plastic housing to make the hot glue within the enclosure melt into all the crevices and hold the alignment cap on. Be careful here because using too much heat can easily damage the plastic enclosure and alignment cap. Once that is done you are effectively finished.

Testing Phase

Although I tend to test at each discrete stage of a repair, for things such as bridged connections between pins or for consistent continuity across connections. I also recommend a final testing phase where we test the resistance of each wire using a USB 2.0 type-A female breakout board and a USB Micro type-B breakout board; or whatever the appropriate boards for the cable you are testing are.

The reason why I do this is to make sure that all the lines are of appropriate conductivity. In other words there aren’t any spikes in resistance in any of the lines that may cause problems when in use. This is especially true for data lines, where resistance will damage signal integrity. Although it is also important for power lines in use-cases involving higher current draws (around 2-3 Amps), such as those used in ‘fast chargers’. If there is sufficient resistance on the VBUS here it will retard the device’s ability to draw power across the cable.

Examples of improvised testing adapters

It’s generally good protocol to have a control test for comparison when testing your repaired cable(s). In this case I used a Samsung brand, model: U2 APCBU10BBE data cable that came new with a smart phone purchase. Please note: the control cable used here is not designed for higher current draws, it’s device needed a maximum of around 700mA to 1 amp when charging.

(Control) Samsung (U2 APCBU10BBE) data cable:
VBUS: 0.2 ohms
D-: 0.3 ohms
D+: 0.3 ohms
GND: 0.4 ohms
Shielding: none
Cable length (approx.): 1 meter

(Testing) Repaired w/kit yellow cable:
VBUS: 0.2 ohms
D-: 0.3 ohms
D+: 0.5 ohms
GND: 0.6 ohms
Shielding: 0.1 ohms
Cable length (approx.): 1 meter

(Testing) Repaired w/spares red braid (‘fast charge’) cable:
VBUS: 0.2 ohms
D-: 0.3 ohms
D+: 0.2 ohms
GND: 0.1 ohms
Shielding: none
Cable length (approx.): 2 meters

As you can see, they tested close enough that I feel that the cables that we repaired are of an appropriate quality, at least for me to have enough confidence to press them into service. Alternatively instead of using a control test for comparison, if you manage to find a datasheet for a particular cable you wish to replicate. The data from the datasheet can be used as a target instead. I just found it easier to see how my everyday cable fairs, then try to ape it’s stats. Consequently I do not have a concrete idea of what the resistance tolerances and acceptable margins are for these cables to maintain signal integrity while in use. But I am confident from the comparisons with the control cable that we are within them.

However, if say a cable tested (pulling numbers from my … hat) 15 ohms on a data line. I would inspect the repair, if it seems fine: then the problem could be with the cable itself. For example: such as in a wire where many of it’s hidden internal strands have broken due to repeated localised flex damage. So all the current is having to pass through just a few strands at that point, causing an invisible bottleneck. This should have been tested for at the initial stages of a repair when the cable was first cut and the wires exposed. But still, finding this fault at this stage, allows you to make the informed decision on how to go forwards, either demote it to a power only cable (and mark it as such), scrap it for parts, or find and fix the newly discovered fault.

Eventually, once you reach a stage where you are confident in a cable’s performance, the repair is truly complete and it is now ready to use. Done. This time for real. Thank you for reading.

References / Sources / Further Reading:

https://en.wikibooks.org/wiki/Serial_Programming/USB#What_is_USB?
https://en.wikipedia.org/wiki/USB
https://en.wikipedia.org/wiki/USB_hardware
https://en.wikipedia.org/wiki/USB_On-The-Go
https://en.wikipedia.org/wiki/USB_(Communications)#Signaling_state
https://www.ifixit.com/Guide/Micro-USB+Port+Replacement/73401
https://www.portplugs.com/how-to-repair-a-loose-micro-usb-port/
https://www.youtube.com/watch?v=36CKsP9YQ1E [why does USB keep changing – NostalgiaNerd]
https://goughlui.com/2014/10/01/usb-cable-resistance-why-your-phonetablet-might-be-charging-slow/
https://www.mschoeffler.de/2017/10/29/tutorial-how-to-repair-broken-usb-cables-micro-usb-including-data-transfer/
https://www.mouser.com/pdfdocs/HiroseZX62Datasheet24200011.pdf
https://www.howtogeek.com/670644/what-is-fast-charging-and-how-does-it-work/