Circuits, Necromancy, and Solder: Board Repair School, Part 1
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Circuits, Necromancy, and Solder: Board Repair School, Part 1

There is a moment, during a tricky fix or DIY project going even halfway right, when you feel like you can see more of the world. You can see how things fit together, how a system works, at a level most people don’t know. It’s empowering and it puts a smile on your face. Maybe it will even save you money someday.

I had one of those rare moments one day last month, staring through a microscope at a microchip smaller than a flake of sea salt. Heating it with 385ºC air from the nozzle in my left hand, the chip suddenly shifted, settling onto 64 microscopic balls of just-melted solder. I lifted the point of the tweezers in my other hand off the surface. With that, I had replaced the chip that regulates charging on an iPhone 6. A couple minutes later, I hooked the newly repaired board up to a screen, battery, and charging port. It worked.

Using a Tristar Tester device to confirm a board is working
A Tristar Tester confirming a successful charging chip replacement.

Replacing the Tristar chip on an iPhone board wasn’t the hardest thing I did at Jessa Jones’ week-long microsoldering and board repair class. But fixing that iPhone board made it all click—this was not something only gigantic companies can do. I was doing it.

This was not something only gigantic companies can do. I was doing it.

The logic board inside a smartphone (or tablet, or laptop, or any gadget) is a grid of flowing electrical channels. When the electricity can’t go where it needs to, you can find out where it’s blocked, and make it flow again. We can fix these things—even I can fix these things, a writer whose last real electrical training was the Science Olympiad in 7th grade. Not every phone can be fixed, nor is the effort or time worth it to everyone. But a lot more of these things could be fixed than we’re fixing now.

What follows is part one of a three-part diary of my week at “board school.” It won’t be strictly chronological, because there’s both repetition and backtracking in learning. This post will detail the major lessons I learned about how phones fail on an internal level, and how to diagnose them. Next week I’ll dive into the work of repairing all those faults, and after that, the business and politics of microsoldering and board repair.

Think Like a Physician, Not an Engineer

iPhone board with a chip removed, and a fingernail for scale
iPhone board with a chip removed, and a fingernail for scale. Each one of those bits with silver on its sides is a component that could fail—and be fixed.

There are almost certainly more circuit boards inside iPad Rehab then there are people in the town where it operates. Honeoye Falls is a 20-minute drive from Rochester in upstate New York. The village has 2,800 residents, five main roads, and one Walgreens. It’s a drab, gray, one-and-a-half hour drive on the Thruway for me from Buffalo, through the leafless trees of early February.

Most of the other eight people in this week’s course have flown in—from Georgia, Wisconsin, Pennsylvania, and North Carolina—save one from Rochester. Three of them already do “parts-level” work, replacing screens, batteries, and the like, and want to offer deeper repairs and data recovery. Three others are from the military, where they recover evidence from phones involved in criminal cases. The other two students don’t plan to microsolder full-time, but might make it a side gig. And then there’s me, the writer who, after hearing about the others’ experience, is wondering if he’s finally signed himself up for a story that proves he’s in way over his head.

We were asked to bring along broken devices. Most brought phones that seem to not boot up at all. Some had phones that booted but didn’t show an image, respond to touch, have audio—known as “boots but” cases in the shop. Me, I had a friend’s Pixel 2 whose display I seemingly killed during a battery swap, and a 2012 MacBook Air that intermittently beeps three times instead of booting.

We’ll probably save most, if not all, of these devices, Jessa tells us. We’re going to train ourselves to think like physicians instead of engineers. Engineer brains run the same tests on everything, testing and comparing each circuit on the board. Physician brains gather as much relevant history as possible, spot and separate symptoms, and know the most likely diseases and rare exceptions. Most of all, a physician intrudes only as much as is needed to get the patient back up again.

Jessa Jones, filming an introduction to microsoldering at iFixit’s offices in 2015

Jessa Jones is a well-known figure in board repair and data recovery circles. If she or her iPad Rehab staff can’t get a phone to boot again, they don’t make money. Unless the board is physically snapped or gouged, or the CPU or storage have serious damage, she can probably get a device to the passcode screen. Some devices are so damaged they might not be reliable for everyday use again, but the number of people who can get back their baby photos, business documents, or text messages from departed loved ones is much higher than you think.

There is, however, one unfixable problem: iCloud activation lock. Our class will bring a completely dead iPhone SE back after a drop in the lake, and jump-start an iPad Mini using two power supplies. But iCloud activation lock is an unbreakable curse if you don’t know the prior owner, and nothing in Jessa’s bag of a thousand tricks can bypass it. Realizing that is a weird moment of sobriety in a week full of defying expectations.

connecting a loose display and battery to an iPhone board
A student at iPad Rehab hooking up “known good” parts to an iPhone board to eliminate parts damage as a potential cause.

We start our training with Rule One of board repair: no device has a board problem until you’ve proven that all the other parts are working. Shops keep “known good” parts around for every phone they can. Before you yank the board out or heat up the soldering iron, you hook up a good screen, charging port, and battery, then see what works. Jessa handed each of us a loose iPhone 6 logic board to test this way. Watching the most expensive part of an iPhone shaken around in a plastic bin or dropped onto tables, seeing students pop screens and batteries on and off with their fingers—I’m convinced my face betrays my careful, step-by-step iFixit credentials.

I get over my precious view of silicon by day two, aided by a teachable moment. I asked Jessa, holding a loose board in her hand while monitoring its voltage intake, if we should ever be concerned about, you know, shocks, or accidentally shorting something, or oils on your hands.

Jessa spun her chair around and lifted the still-connected board to eye level. “See this charge port?” She licked it. “It’s only a few volts, Kevin. Do you wear shoes with soles? Do you stand in a tub of water while you’re working? It’s fine.”

Jessa will spend a good portion of the week disabusing me of various notions I’ve picked up in my career writing about technology. She didn’t tread lightly on anyone’s ego, and quickly honed in on the issues each of us brought to class from our lives or careers. Case in point: only two days into class, she diagnosed most of my soldering and diagnosis issues as “a moderate to severe case of Overthinking-It-itis.” It was one of the most strangely kind and encouraging ways I’ve ever been completely owned.1

“See this charge port?” She licked it. “It’s only a few volts, Kevin.”

Shot from behind of Jessa Jones teaching her board repair class
View from the author’s chair as Jessa Jones examines a water-damaged board under a microscope.

The hands-on portion of our repair journey begins with learning how to read a board with our eyes. Peer closely and you’ll see wires, ports and their pins, pathways that connect to the board’s metal (ground), and “vias,” sub-surface wires that connect to the pads underneath each chip. Most importantly, we learn about the different kinds of solder: the lead-free kind factories use, the standard lead/tin most people use, and the high-end bismuth/tin stuff.

This introduces one of many paradoxes in responsible electronics. Manufacturers largely dropped lead solder in the mid-2000s. At the scale they produce devices, going lead-free makes a big difference for the earth. Lead-free solder, however, is more brittle. Using consumer-grade lead/tin solder actually improves the strength of the connections on a board. And you’re using very, very little of it; Jessa has been working from the same used spool she bought on eBay her whole career. “Companies make their environmental impact by going lead-free. We’ll make ours by making devices last as long as possible,” she told us.

Boards and wires and solder are the precursors to learning about the working bits of the board they connect. On day two, we learn about capacitors, resistors, transistors, filters, chokes, diodes, buck and boost converters, mosfets, and coils. Using a multimeter, mostly in diode mode, with the red probe on ground, you poke at components and look for three key failure readings:

  • Open (or “broken open,” as Jessa prefers), when a component fails and leaves the circuit incomplete. The multimeter reads “OL” (“open loop” or “overload”). The circuit has no continuity, and has nearly infinite resistance to the ground.
  • Short, an unintended connection, usually to ground. The multimeter reads “0.0,” because there is no resistance between the probe on ground and what you’re poking—it’s already going to ground.
  • A resistance reading hugely different from the typical resistance readings on your schematic or crowdsourced diagrams (more on those in just a bit).
Testing an iPhone's logic board with a multimeter
Testing an iPhone’s display port connectors with a multimeter (and a port-testing connection tool just out of frame)

It’s a lot to absorb, but there is good news: that’s basically all the required reading for Microsoldering 101. The reason your phone dies when you drop it, bend it, dunk it in water, or charge it with unstable power is because one of those board components is short, open, disconnected, or damaged in some weird way.

The Usual Suspects

How do you know which component died on a seemingly dead phone, when there are hundreds and hundreds of the little buggers? If you’re experienced, you might have a good guess before the screen comes off.

Certain thin filters tend to burn out when a lazy technician connects a screen with the battery still plugged in. Water tends to invade phones in familiar places, like near the SIM card slot on the “water resistant” iPhone X. The iPhone 6 and 7 bend more than others, causing tiny solder ball connections beneath chips to crack or come loose, leading to “Touch disease” on the iPhone 6/Plus and frequent audio IC issues with the iPhone 7/Plus. Any time there have been prior repair attempts or parts swaps, by a tech or DIY, you check for “long screw damage.” At a board repair shop, these esoteric issues are as common as a scratchy throat at an emergency care clinic.

What happens if you don’t recognize the problem from the symptoms? You run some tests and examine the board. One easy test is plugging a cable attached to a USB ammeter into the phone and watch as it boots up. Just from watching the amperage ascend, loop, or get stuck at an unusually low level, you can tell a lot about the phone’s state: booting, stuck in DFU mode, “brain dead” from CPU or storage damage, and so on.

Now that you know the phone’s general condition, it’s time to pull out the board and look for the problem. There are three main tests:

  • Visual: Look at the board under a microscope. Which parts are corroded, burned, have cracked or dull solder? Or, you know, missing?
  • Heat: Give the board power for a moment, and see which components become exceptionally hot much faster than their surroundings.
  • Brute force: Test every component through every related circuit, physically removing them as you go, if needed.

You might be asking, “How can you see which components get hot?” Thank you for asking, because the answer is awesome. Using a phone-mounted thermal camera, you can see a white-hot component stand out on a board that is still just-booted blue. A cheaper approach is to hit it with freeze spray and then watch which short/hot component visibly melts its coating before everything around it. Cheaper still, but probably inadvisable: hold the board against your face, like Jessa would sometimes do when she was first starting out.

Looking closely at a thermal camera hovering over an iPhone board
Using a thermal imaging camera to spot the hot short-circuited on a phone board.

By this point, you might know which bit on the board is acting up, but not what that bit does, or what else is on the same circuit. Not even Jessa knows every capacitor from memory. This is when you turn to giant PDFs you’re not supposed to have, and some sketchy Chinese  software.

Schematics and Software that Fell Off a Truck

Schematics are a diagram of every component on the board and the electrical lines running between them. Good schematics are PDF files that are fully text-searchable, so you can follow, say, a USB_VBUS_DETECT line you think is acting up from the battery to the USB controller chip, with a stop at a resistor along the way. It sounds complicated, but the work is mostly Control/Command+F searches and interpreting naming schemes.

Some companies, like Samsung, will sell you schematics. Apple does not sell or offer schematics outside its production chain. But people find them, and repair shops that do board repair rely on them. If a Right to Repair bill became law, companies would have to share schematics with repair shops trying to fix their devices. For now, they’re a murky area all repair techs must muddle through.

Part of a backlight driver diagram inside an iPhone schematic. You can see a BGA-style chip named U1502, the voltage on a line leading to it (PP1V8 = 1.8 volts), and lines running to “AP,” the application processor, or CPU. Other components in the circuit include a coil (the rounded hills at L1503), a diode (right-facing triangle above the chip), and capacitors (two parallel lines, shortly above an inverted triangle of ground).

Schematics can answer your questions about what each little bit is, what it does, its normal resistance and voltage, and more. But actually working with a giant PDF schematic by itself can be frustrating. You have to flip between multiple pages to follow a single circuit, and the naming schemes are not optimized for a layperson’s comprehension.

That’s where board view software comes in. Board view apps are a convenient organizing layer built on top of schematics. They make finding a component and tracing the circuit it’s on more like playing SimCity than finding a drain in a sewer diagram. From an overhead view of the board, you can click or name search for the component where you suspect problems, and everything else connected to that component gets highlighted.

Jessa, like most board techs, uses ZXWTEAM, a.k.a. Zillion x Work. The name is an earnest pitch that your repair shop will have a zillion times more work if you use it. The app is not user-friendly and triggers anti-virus warnings on many computers. The authentication servers are in China and it’s hard to buy in the U.S. (though Jessa sells licenses). We don’t sell it on iFixit because our lawyer told us not to. But it’s essential for anyone doing board repair.

What We’re Really Learning

Unlike most college courses, Jessa’s board repair school made it clear why you had to learn the theory and science behind board repair before you start dragging a hot iron across the board. Practically, it saves you time in figuring out what the problem part is, and keeps you from doing unnecessary work. But it also reconfigured my understanding of what a “broken” device means. The majority of consumer gadgets that stop working are almost never entirely “broke.” Their electricity isn’t flowing, and something needs replacing, removing, or reconnecting to make it flow again.

That might not sound revelatory to anyone who’s spent a lot of time researching the devices they use to send emoji and check the weather. But it’s been a momentous journey for me. Since smartphones and tablets arrived in my life, my relationship with them has gone through a Galaxy-Brain-style evolution:

  • “This phone’s battery is dead, time to get a new one”
  • “Maybe a shop can replace the screen or battery”
  • “Actually, I can replace the screen or battery”
  • “Okay, but this phone suddenly stopped booting, so now I need a new one”

The next and final stage, well, that’s what this class was: you can fix the brains of a phone, too. Because the brains are just tiny wires. If you have the equipment to look at tiny things, you can make the tiny changes necessary. You also have to care enough to do so.

One of the cases a student brought in was iPhone 6 that had been through hell. The backlight was dead, neither speaker worked, the Audio IC chip seemed to have failed, and some other chip was just gone. The phone had already been to Apple and back, and two other repair techs had tried their hands at it. But Jessa discovered what every previous tech had missed: a resistor, right by the CPU, that was faulty.

Resistors are tough and rarely fail, but when they do, they leave a line open. Pulling a replacement from a donor board, Jessa patched it in. She peeled off the screen’s original backlight, held the display against her microscope light, then plugged it in.

An iPhone screen lit up by a microscope camera

The Apple logo appeared. The passcode screen came up. The class cheered. I wrote in my notebook: “I am a convert now. That was legitimate necromancy.” I no longer felt like I was in over my head, but instead like I had just joined some secret society. 

Next week, we’ll detail how you pull off fixes like that: heat, solder, flux, shiny little chip balls, and the other stuff of actual board repair. Spoiler alert: you might find out that manipulating tiny things looks easy when Jessa does it (Me? Not so much).

[1]: Sources for the accuracy of this statement include: my second-grade teacher’s handwriting assessment; my eighth-grade wrestling coach; every editor who has read something I had more than one hour to write; my wife, regarding her request to pick up “some fruit” at the grocery store.