Adventures in Splicing an HDMI Cable
We just purchased our home here in Austin, Texas, and were super stoked to find out that the WHOLE house was wired for audio.
The downside was that once we built out shelves, mounted the TV, and set up all the equipment that the male adapter of the HDMI routed through the wall was – well… f@*kd.
I didn’t find any thorough, clear, and effective approaches of splicing an HDMI cable, so I’ve decided to log and then blog my efforts!
I originally set out to write a single, succinct-yet-thorough, fully-encompassing post. Problem is, I ramble on way too much, and tend to think a lot of the information I found out is useful to share.
I originally wrote this in 2014, and releasing it now in 2017 and would like to report that everything is still fully functional without any re-work. Also, I lost some of my images, which is why I never released this, but figured why not…
You also need a high level of patience, and an understanding that you might not get it the first try. There’s also a lot of pictures, because I wanted people to see what they were getting into, which I didn’t see a whole lot of nice pictures when researching.
My suggestion is to get all your tools ahead of time (see at the end of the list of tools I utilized); otherwise getting up and heading to your toolbox or, worse, the store will frustrate you and frustrate you to the point of getting sloppy. You can NOT get sloppy with this process.
Preparation of you cables is key. Clean stripping of wires and sheathing, and understanding the HDMI configuration is also very important. I’ll be giving a quick run-through, but will resource some links at the end of this post that will detail more information for you.
With all that said, I was able to accomplish this in two tries (spanning a total of 8-10 hours, in separate sittings). I suspect with what I know now, I could have actually been successful on my first attempt with a bit more patience.
Quick HDMI knowledge-dump
HDMI is very delicate in operation; all signals on all wires need to terminate at both ends cleanly, and all electrical currents need to be synchronized when they hit the termination point. Longer cables over 50ft will have “equalizers” in them that do exactly this, and an HDMI repeater will also synchronize before re-broadcasting the signal. That means do your damnedest to have all wires cut and soldered to near-exact lengths.
Here’s a few quick demonstrations of the HDMI connector, and the cabling bundles inside the HDMI sleeve:
HDMI Pin-Out, courtesy of HowStuffWorks.com
Another great Pin-Out showing bundling inside a cable, courtesy of cepro.com
An interesting aside, Pin 19 (Hot Plug Detect, or HPD) is 50% shorter than all other pins. This means that if your cable isn’t plugged in all the way (or the contact point is recessed in any excess) you’ll be sure to get HDMI handshake issues.
Around the bundle of cables is a braided shield (shown later in my dissection pictures) to avoid interference via a Faraday configuration. I’ve read by the leading manufacturers that this actually doesn’t do all that much in an HDMI cable, since there’s more shielding done internally. I’ve also seen a video of a guy stress-testing a cable, and it’s evident the shield is by far not the last resort of protecting the cable. Often times, a manufacturer will include every little shield concept (which will be detailed a bit more) as a “bonus level of shielding.” Don’t fall for this; the HDMI standard requires enough shielding to avoid most issues.
Underneath the braid, the entire set of cables is wrapped with aluminum foil tape as another global shield and more importantly a ground.
Each of the “groups” (a.k.a twisted pairs, or in some/most HDMI cables, twisted triplets; see the pin-out image provided for reference) include a positive, negative, and a drain wire.
The drain wire acts as an additional interference shield, and connects to the global aluminum shield and to the ends of the cable sheathing in the connectors’ molding.
Each group is then shielded by aluminum foiling, and a clear plastic sheathing. On shorter cables, the drain wire will be on the outside of the bundle, and on longer cables where shielding is even MORE important it will be along the positive/negative cables (as pictured above). I found in the splicing, it doesn’t matter how you do it, since it’s likely you’re splicing a short piece. If splicing a longer (think many many feet), I suggest going the twisted triplet route.
In all the cables I’ve cut open so far (a whopping count of 7 /s), I found the negative wires in all groups are the exact same color (in my case, they were white in every cable I cut open, but that doesn’t matter), and the positive conductor wires were all uniquely colored (I’ll touch on the topic more in the mapping section).
I’ll get into troubleshooting near the end. Stay tuned!
Assessing the situation
Simply put, the HDMI tip was bent and partially broken off. After trying every wiggling tactic in the book, I decided it just wasn’t going to work.
It’s never as simple as it appears… Ever…
Stepping back, I quickly realized I had a serious case of Hanlon’s Razor going on (derived from the previous owner’s installation technique), with a serious case of Finagle’s Law (very similar to Murphy’s Law). The ends weren’t terminated with face plates for HDMI in/output; which would have at best been a LOT simpler to replace, and limited possibilities of damaged parts.
“Why don’t you just get a new cable?” you might ask. Well, mostly because I’m cheap… or broke, you decide (we did just buy a house, after all).
But the labor required in our house was more than the average. First off, the house is two stories, so to go from the first floor, to the attic, back down to the first floor was going to prove to be EXTREMELY difficult, if possible to find anyone to do it at all. Secondly, short of easy routing, we’d need to start cutting a channel out of the drywall from start to finish, as there’s foam insulation in the walls (think Great Stuff type foam; it’s sprayed in and hardens). This increased labor immensely, since there would have to hand scraping a channel for wiring (and if I’m going to do it right, a conduit) the entire path. Not to mention the walls are smooth (no textures), so repair has to be perfect, or it’s glaringly obvious.
Also, I’m partially a glutton for punishment via odd experiments and projects.
Now that I got that out of the way, let’s just get right down to the nitty gritty.
First, a few shots of the damage at hand:
This is the end that would have gone into the receiver, underneath the stairs, a good 45-50ft in a direct line (which of course you know it isn’t routed that way). So it has to be much longer. The gold-plated HDMI connector pulled off rather easily, and exposed the pins you see.
What’s not so obvious here, is that I’m actually holding it upside down, and the pins showing are the bottom row (odd numbered pins, which we’ll get to in a bit) and the top row of pins actually broke off and were left inside the connector (outlined in red).
Mapping your HDMI cables
If you’re familiar with electrical, Ethernet, and other well-known (long-lived) types of cabling, there’s typically a standard of colors for internal wiring.
Unfortunately, this is not the case with HDMI. In fact, the running “joke” (read: mega-annoyance) is that every manufacturer’s HDMI cable is a snowflake. No two are [intentionally] alike (with exception of matching manufacturer and cable “model”). With that said, the first thing to do is to map both cables.
Since I had cut the broken end off, and had spare HDMI cables laying around, I cut a perfectly working cable and began to strip both cable ends.
Some shots of dissecting the cable:
Notes and Quick Tips
The biggest thing to note is I opted to delete the braid, and foil. This was simply because on a broken end, it got in the way while I was figuring everything out.
DO NOT DELETE THE BRAID AND FOIL on final pieces. The foil is critical to proper shielding and the braid helps avoid re-bundling issues at the end of your project.
This also goes for the internal twisted pairs/triplets.
To keep these items out of the way, slide down the braid, and fold back the foil, and use masking tape to hold it down.
To avoid the tape from being too sticky, and potentially ripping the foil later, tape it to your clothing a few times to reduce the stickiness. If necessary, apply a clean piece of masking tape around the “de-stickified” piece to ensure it won’t pop off while you’re working (this keeps the foil staying down, without adhering to the foil itself too well – you don’t want it to rip!).
I only had a wire stripper that supported “down” to 22AWG wire. This was fine for the twisted triplets in the original cable, but the other wires, and ALL the wires in my replacement cable were at least 26AWG; really small. The first time I attempted, I stripped the wires I could with the wire stripper, and then used a lighter to melt the enamel off the smaller wires. This worked, but I’m a wuss, and the plastic burned the hell out of me. The second time around, I took time to practice with a wire cutter to perfect getting the wire sheathing off perfectly, every time. I suggest you learn this, as it not only sped up the whole stripping process, but your wires won’t have any residue, allowing solder to later bond better.
I’ll get into it more later, but give yourself enough exposed wire (with sheathing, not the copper wiring itself) to be able to slide on heat shrink later. You want to 100% avoid any unintentional contact!
Now on to the actual mapping
Because the tip of the original HDMI cable broke off, I was lucky enough to be able to simply create a circuit with my multimeter to figure out which cable mapped to which pin.
You really only need to map the positive wires in the 4 groups, and the rest of the various wires not in the groups. From my experience, the negative wires in the groups are always the same color, but either way, when you know the positive wire, the only other two are the negative and the drain wire. The drain wire should always be bare, so try not to damage the ends too badly when handling it.
The other various wires will likely not be similar colors to the other HDMI cable you’re using, so be sure to label things clearly. I opted to use a text editor to maintain the color mapping, and loaded it on my phone while I was doing the actual solder work.
On the new HDMI cable, you won’t have the pins exposed (hell, maybe in the original you won’t either), so you’ll have to fashion a shorting wire. I had some spare 28AWG wire laying around from my previous console modding days, so I stripped the ends of a good length (around 7-8 inches).
Wrapping an exposed end of the wire around one of the probes of the multi-meter, and having the other end of the wire pushed into the HDMI connector. If you look closely, the perimeter of the connector has little holes that give access to the pins without damaging them (see pictures to see correct placement), which makes it easy to isolate which pin you’re detecting.
At this point, you should have at least 11 wires identified per HDMI cable. The remaining 8 wires are the negative and drain wires per the 4 groups.
Getting to Work!
If you’re following along, we should have carefully and methodically mapped out the wire colors to pin numbers, and prepared the cables for soldering.
The following portions are going to mostly be tips and tricks for how I managed to pull this off.
As stated in the first post, in the preface – you MUST have patience!
Be sure to have everything ready – it’s super annoying to be in the middle of your project, to find out you need ONE more thing.
In my situation, the cable was coming out underneath the stairwell. Luckily, there was enough length to pull it a few feet out of the hull where I installed media shelves for my equipment. This allowed me to fabricate a “workstation,” and count my blessings I wasn’t doing this upside down under the stairs! I had a cheap little glass/metal patio table that was the perfect height, and I knew it would be hard for me to damage it.
The longer and heavier the cable, the more it will be a huge pain to work with; it will want to twist, fall, and tug on your solder connections. There’s actually a simple way to avoid a lot of issues. I simply taped the cable down to my work table with enough slack that I could manipulate the cable if I desired, but it wouldn’t pull back on me and cause turmoil.
I quickly realized it’s probably easiest to work with the groups first (they naturally want to bend/face/twist together since they’re shielded together). I later found out they are also the most fragile (the shield termination has to be perfect). To help organize and keep things out of the way, I taped the four groups together using the same de-stickify technique I mentioned in the earlier posts. Then I grabbed ALL the wires I wasn’t currently working on, and folded them back and taped them to the main cable sheathing. You might overlap tape from your foil, so be sure it’s not super sticky on the other tape piece or you’ll be fighting it later.
These last few tips are more preparation, but will improve chance of success when going through the solder process:
- On both cables, attempt to strip the wires exactly the same length. See more in the tips under the Process section.
- Tinning the wires before starting can make things a lot easier, instead of working in close quarters. I would do this next time for sure, because it’s quite a job to manage tinning and not breaking another solder connection.
- Don’t pre-cut heat shrink tubes – when you get closer to the end, you end up wanting to use less and less to avoid over-bulking the cable.
- DO remember to get and cut an outer heat shrink tube. I went with a 1/2″, which was mostly appropriate for my size cable. As I completed and was finishing up, it was SUPER hard to squeeze it over the work to the other side. I was constantly worried I would rip the tube, but it worked out. Has a nice tight squeeze, and can barely tell it’s modified.
- Be ready with the flux. I used a tin foil square, and squeezed some out for quick access, to be applied by toothpick. If you use a paste instead of a gel, I suggest you scoop some out. Remember, you’ll be working with two cables that will be bound by 19 cables in the end – you won’t be able to simply place the end of the wire in your paste.
- I used a cardboard box on its side as a makeshift table next to me, where I put my flux pad, various shrink tube sizes, dykes, and inside I placed some foil to put the heat gun on and out of the way when not used. Point is, it’s best to keep items close and easy to swap when working on a small project with lots of needed parts like this one.
- Be cool, calm, and collected. Frustration and distraction will cause you to get sloppy and things won’t work. I jammed to 90’s rock to keep my inner-Chi.
- Also have proper lighting. I had a pink, light pink, and a purple cable that under dim lighting looked identical. I actually got it wrong early on, and caught it later when I realized it was too dark with 2 more wires left and turned a light on.
The process isn’t really any different if you’ve ever soldered, but I’ll give the simple steps here:
- Apply flux to both tips of wires.
- Tin wires with solder; let cool.
- Measure enough heat shrink to cover the exposed tips, and cut. Slide over working wire set.
- For this project, don’t shrink these 100% when applying; just enough to stick. You’ll be reheating the work area quite often due to the close proximity of the 19 wires; you don’t want to over heat and melt it, or make it brittle and break apart quickly.
- Solder first/positive wires together.
- Heat Shrink with gun.
- Twist secondary/negative wire around first as best as you can.
- Solder second wire.
- Heat shrink second wire.
- Depending on configuration, apply foil first, OR wrap drain wire around the sheathed wires. I don’t think it matters in the end, as one of my wires was configured to wrap outside the foil, while the other wrapped inside the foil. I opted to wrap inside to make foiling easier.
- Foiling process is simply ripping a sheet of aluminum foil, and carefully wrapping the foil around the group of wires. You want both ends of the foil to firmly touch the original shielding from both of the original cables.
- Once firmly in place, wrap well with scotch tape
- Heat scotch tape with gun, and it will apply a protective sheathing around the foil and group of wires.
- Rinse and repeat for the rest of the 3 groups.
- Wires 13-19
- Simply solder matching wire configurations and heat shrink.
Tips and Troubleshooting
When starting the solder process for each wire, be sure to overlap the wires. You don’t want just the tips to connect, but a good solid connection. This correlates to the first tip in the Preparation section. With the tips cut identical length on both wires, you can ensure that a 100% overlap of the adjoining wire tips will give you identical length in all connections, creating a heterogeneous-in-length wire – WHICH IS CRUCIAL!
Wrapping this up
On my first attempt, I botched the foil sheathing and got absolutely nothing. Took me many hours, I’d estimate 3.
On my 2nd attempt (yeah, another ~3 hours), I was getting a few weird results, that seemed random:
- No video
- Video on for a second, then flicker off for a few seconds
- Video displaying in weird colors, then look like a video freeze
- Decent video, but a line going through it
Obviously this is bad… All that effort! Fret not! Before I did my final shrink tube around the whole ordeal, I started jiggling wires. I narrowed it down to a single group of wires, and easily took of the cellophane/tape and foil. After some inspection, I realized that it would only really stay on if I used a scrap piece of aluminum foil to shield the cable as best I could. I then knew my shielding job wasn’t done well on that group. I reapplied the shielding, being sure to get some extra foil shoved into the sheathing for a good contact to the original foil shield, and reapplied the scotch tape sheath.
After 20 minutes of playing a video, I determined the cable was good and cleaned up shop. Gave everything a once-more with the heat gun, then slipped the outer tube over, and shrank that.
As mentioned before, it’s been working for 3 years without any issue!