A Simple Display Repair - and Why It’s Not Economical

17 Aug 2025 - tsp
Last update 17 Aug 2025
Reading time 7 mins

Recently, I repaired a 4K UHD AOC monitor. But this article isn’t about that particular model - it’s about what the experience always reveals: repairing modern electronics is often technically simple, but economically irrational. Let’s dive into why.

The Repair: One Capacitor, Less than One Hour

The issue? One of the most common and classic ones in todays displays and TVs - as well as many other appliances: a swollen low-ESR capacitor on the power supply PCB. Specifically, a 47µF 50V electrolytic capacitor, sitting right at the heart of the switching MOSFET stage in a standard flyback converter circuit. These capacitors are commonly used for smoothing the output of high-frequency switching regulators or supplying bootstrap voltage to the gate drivers, and they’re exposed to substantial ripple current and heat. A degraded low-ESR capacitor in this location causes ripple instability, reduced voltage stability, and ultimately failure to boot the display.

The power supply PCB. The defective 47µF 50V capacitor is marked in red. It sits right next to the switching MOSFETs.

These capacitors are often placed very close to the switching MOSFETs, which are required for high-frequency switching in the range of tens to hundreds of kilohertz - sometimes even in the megahertz range. This enables the use of compact flyback transformers, reducing transformer material usage, improving efficiency, and minimizing energy losses. Due to electromagnetic compatibility (EMC/EMV) regulations - which are in place for valid reasons - these capacitors must be positioned physically close to the MOSFETs to suppress high-frequency noise and reduce radiated emissions. Consequently, they endure substantial thermal stress from both the MOSFETs and the switching process itself, which accelerates aging and increases failure rates.

There is a common rumor that manufacturers place these capacitors so close to heat sources on purpose to reduce product lifetime - what some people call “planned obsolescence”. But this placement is not a conspiracy; it’s a technical necessity driven by physics. In fact, manufacturers typically use capacitors rated for high temperatures (105°C or more), and when high-quality components are chosen, they are often rated for up to 50.000 hours of operation at those elevated temperatures. But nevertheless after extended periods of operation they dry out - sometimes they pop up open releasing the magic smoke, sometimes they ignite and sometimes they just show a bulge and have massively increased

internal resistance and massively decreased capacitance. Or they short out.

The removed capacitor. The bulge is a classic symptom of internal degradation due to heat and ripple stress.

Once identified, the fix is trivial. Desoldering the part took less than 30 seconds. Soldering a new one, likewise. Cost? Less than a cent per part, assuming you buy a pack of 100 for 0.13 Eur for the whole pack.

The Real Work: Getting In

The challenge for this particular device wasn’t electrical. It was mechanical. The monitor had zero visible screws. Disassembly involved carefully “popping” open the plastic bezel without damaging the device - a process filled with uncertainty unless you know exactly where the internal hooks are and how they’re oriented (this is where teardown videos on YouTube usually help - there hasn’t been one for this device and I forgot to make a video - again). Trial and error usually leaves visible damage or breaks the housing.

Then came the glue. Internal parts were held with adhesive in places where pulling too hard risks tearing cables. This added hours of disassembly time. Only after reaching the power supply PCB could I spot the bulged capacitor - and even then, the markings were partially unreadable. Understanding the circuit confirmed it was a low-ESR 47µF 50V cap.

The capacitor has been removed. Only the footprint remains.

A view from the underside of the power supply PCB — often more beautiful than expected!

After unsoldering it turned out the capacitor only had a capacitance of 17µF at this moment and a extremly high series resistance. Note that when you are doing this more often with power supplies it’s a good idea to just change all electrolyte capacitors when you are already repairing something. Just build up a good stock of low ESR capacitors and the most common parts. Do not go cheap though - cheap capacitors die magnitudes faster. And never use general capacitors in place of low ESR ones.

The new capacitor installed. A high-quality low-ESR model rated for 105°C, expected to last tens of thousands of hours.

The new capacitor installed. A high-quality low-ESR model rated for 105°C, expected to last tens of thousands of hours.

Ordering replacements added four days of wait time.

Reassembly: Tape, Not Screws

Rebuilding the monitor was quick. Conductive tape holds most parts together, not screws. Final testing took less than five minutes, and the monitor worked perfectly again. Note that the usage of conductive tape is not optional. This completes the grounding of the panel as well as the EMV shielding.

The reassembled monitor. Most internal components are held in place with conductive tape instead of screws.

So Why Is This Not Done Professionally?

Because even though it’s simple it’s not economical. Here’s the breakdown:

That’s without front office workers that handle your turn in, no shipping, no carrying around. Just the plain repair. The price of a new 4K UHD monitor? Around 300–600€, depending on specs.

So unless the repair is done by a hobbyist for personal use, it’s uneconomical. Even worse: You have of course no warranty on the device any more after such an repair - and if the repaired device causes damage (say, a fire), your insurance (when residing in European countries) most likely will not cover it due to the unofficial repair. They will not even care about the repair being done correctly or not, it’s just the unauthorized repair that counts.

Repair is Easy. But the System Is Broken.

This repair highlights how simple many electronics repairs still are from a technical perspective - it was the most typical fault in today monitors and TV sets - about en-par with shorted or opened background illumination LEDs that are about as simple to diagnose and change (the ominous blinking screen effect). For skilled individuals, fixing such issues can be quick, cheap, and rewarding. However, the overall economic picture is another story: high labor costs, lack of warranty after repair, logistical hurdles, and complex disassembly processes make these repairs unattractive on a professional scale.

Still, developing basic repair skills can be incredibly valuable on a personal level. Even just the ability to identify and replace a faulty capacitor can save hundreds of euros. As we move further into a technology-driven world, making such skills more accessible — and perhaps reconsidering who is legally allowed to perform them - might help reduce unnecessary waste and ease the financial burden for individuals.

Useful Utilities

The following section contains a list of useful utilities for debugging and repairing products like the mentioned display.

Note: The following link are affiliate links. This pages author profits from qualified purchases

This article is tagged:

Data protection policy

Dipl.-Ing. Thomas Spielauer, Wien (webcomplains389t48957@tspi.at)

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