A few months ago my 11-year-old Samsung TV developed an interesting fault where whenever I turned it on it would have a lot of trouble achieving a stable audio and video signal. It would show a distorted picture, often accompanied by unpleasant noise, and then reboot after a few seconds having apparently detected that things weren't right.
At first, one cycle was enough and then it work work. In the following months it started to require two reboots, then three, and by the time I started looking into the possibility of repair it would sometimes take maybe 15 minutes of rebooting before it would stabilize.
Fortunately, this is apparently a common fault with this model of television and the solution is documented in several forums online. (Unfortunately I waited a couple months from doing my initial research to attempting the repair, so by the time I got there I'd lost track of exactly where I got the information originally.)
Perhaps due to the age of this television, it's easy to take the back off and access the boards inside.
There are two obvious circuit boards inside. The brown one on the left seems to be the main power supply board and it also contains the relays that I can hear click when turning the TV on and off. There are several power cables leaving that board to various other parts of the television, one of which goes to the green board on the right which is the main logic board for the television.
This particular fault concerns two components on the logic board: an MP2363 step-down regulator and a supporting 47uF tantalum capacitor connected to it. I didn't perform any detailed troubleshooting because a solution was already well documented: replace both of these components.
The two parts in question are placed on the bottom side of the logic board, so I removed the board and flipped it over on my workbench to identify them.
Replacing the Faulty Parts
I ordered replacements for these two components on DigiKey: 1589-1366-ND for the regulator and and 718-2050-1-ND for the capacitor. The main task here, then, was to remove those to components from the board and put the new components in their place.
The usual way to do this is to use a hot air rework station, which is essentially a specialized heat gun used to reflow the solder holding those components so that they can be safely removed.
Unfortunately, I don't yet have a hot air rework station in my toolkit. When I work with surface-mount components in my own projects I just solder them by hand using my soldering iron.
However, by coincidence I had recently learned about Chipquik SMD-1 solder alloy, which is an unusual formulation of solder that is designed to remain molten for much longer than everyday solder wire, so that the user can mix the alloy in with the existing solder to keep the solder on all of the package connectors molten long enough to easily remove the part with tweezers.
For my first attempt with it I did a bit of rework on an old project PCB I had, and it worked well. After I thought I had the hang of it, I then tried the Chipquik alloy on the tantalum capacitor. This didn't go quite as smoothly as I hoped, mostly because I was a little clumsy in how I applied the alloy and ended up with far too much for the size of the component.
However, after some cleanup with solder wick I was eventually able to get the capacitor off. I then moved on to the regulator, which was a tricker proposition due to it being an 8-pin SOIC package with a hidden surprise under it.
What I didn't realize at this point — though in retrospect I should've expected it — was that the regultor package had a thermal pad underneath that was also soldered to the board. Although I was able to remove a lot of the solder on the eight package pins, there was no way to get the Chipquik alloy under the chip to detach the thermal pad.
Unfortunately I realized what was going on too late: while attempting to remove that chip I inadvertently broke it in half, leaving the bottom of the package still attached to the board. Sadly I didn't get that part on video, because in the process I accidentally knocked the board out of the view of my video microscope!
After some head-scratching I remembered that I recently took delivery of a REFLO Air after backing the crowdfunding campaign some time ago. This tool incorporates a heat gun, though it's designed for relatively low-temperature soldering and so ultimately I ended up using a combination of the REFLO Air and my soldering iron to remove the remants of the chip and expose the pad underneath.
After this unexpected diversion I had now been spending a lot longer on this than I intended and so I didn't have the presence of mind to take photos or video of the remaining steps. However, having now got familiar with the REFLO Air I placed the replacement regulator and capacitor using solder paste and hot air rather than my soldering iron, which was surprisingly effective once I got the hang of applying the solder paste to the pads using a toothpick.
After getting both of the replacement components attached I put the board back into the TV, crossed my fingers, and turned it on. Sadly, on the first try the logic board didn't seem to be powering up at all, and the power supply board kept power-cycling it every 10 seconds or so presumably noticing that it was not functioning as expected.
After some further probing with my multimeter I noticed that at least one of the regulator pins hadn't made a good connection with the board: consistent solder paste application takes practice! I supplemented it with a bit more and reflowed it one more time and then... it worked!
On Repairing Stuff
I've been pretty frustrated in recent years by how impractical it has become to make repairs to consumer electronics stuff, and thus how much e-waste is produced by the disposal of a device as soon as even one part of it malfunctions.
The drive to make our handheld devices smaller and smaller makes hand-rework increasingly impractical, but I was pleased in this case to find that this TV seemed to be designed for this sort of repair work: the back of the TV was easy to remove, all of the boards were easy to detach and reattach from one another using board-to-board connectors, and the boards themselves were easy to remove.
I'm not sure if today's "smart TVs" are still so easy to repair, but I sure hope so: TVs don't need to be so compact, and so there's room to design them for repair. Connectors and mounting hardware add cost though, and these modern TVs seem to be sold on very tight profit margins. On the plus side, hopefully repairing my old TV will allow me to defer purchasing a smart TV for at least a few more years.