White LED Turning Purple: Analyzing A Phosphor Failure

May 30, 2025 by Maya Posch 31 Comments

White LED bulbs are commonplace in households by now, mostly due to their low power usage and high reliability. Crank up the light output enough and you do however get high temperatures and corresponding interesting failure modes. An example is the one demonstrated by the [electronupdate] channel on YouTube with a Philips MR16 LED spot that had developed a distinct purple light output.

The crumbling phosphor coating on top of the now exposed LEDs. (Credit: electronupdate, YouTube)

After popping off the front to expose the PCB with the LED packages, the fault seemed to be due to the phosphor on one of the four LEDs flaking off, exposing the individual 405 nm LEDs underneath. Generally, white LEDs are just UV or 405 nm (‘blue’) LEDs that have a phosphor coating on top that converts the emitted wavelength into broad band visible (white) or another specific wavelength, so this failure mode makes perfect sense.

After putting the PCB under a microscope and having a look at the failed and the other LED packages the crumbled phosphor on not just the one package became obvious, as the remaining three showed clear cracks in the phosphor coating. Whether due to the heat in these high-intensity spot lamps or just age, clearly over time these white LED packages become just bare LEDs without the phosphor coating. Ideally you could dab on some fresh phosphor, but likely the fix is to replace these LED packages every few years until the power supply in the bulb gives up the ghost.

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The Cost Of A Cheap UPS Is 10 Hours And A Replacement PCB

May 29, 2025 by Maya Posch 26 Comments

Recently [Florin] was in the market for a basic uninterruptible power supply (UPS) to provide some peace of mind for the smart home equipment he had stashed around. Unfortunately, the cheap Serioux LD600LI unit he picked up left a bit to be desired, and required a bit of retrofitting.

To be fair, the issues that [Florin] ended up dealing with were less about the UPS’ capability to deal with these power issues, and more with the USB interface on the UPS. Initially the UPS seemed to communicate happily with HomeAssistant (HA) via Network UPS Tools over a generic USB protocol, after figuring out what device profile matched this re-branded generic UPS. That’s when HA began to constantly lose the connection with the UPS, risking its integration in the smart home setup.

The old and new USB-serial boards side by side. (Credit: VoltLog, YouTube)

After tearing down the UPS to see what was going on, [Florin] found that it used a fairly generic USB-serial adapter featuring the common Cypress CY7C63310 family of low-speed USB controller. Apparently the firmware on this controller was simply not up to the task or poorly implemented, so a replacement was needed.

The process and implementation is covered in detail in the video. It’s quite straightforward, taking the 9600 baud serial link from the UPS’ main board and using a Silabs CP2102N USB-to-UART controller to create a virtual serial port on the USB side. These conversion boards have to be fully isolated, of course, which is where the HopeRF CMT8120 dual-channel digital isolator comes into play.

After assembly it almost fully worked, except that a Sonoff Zigbee controller in the smart home setup used the same Silabs controller, with thus the same USB PID/VID combo. Fortunately in Silabs AN721 it’s described how you can use an alternate PID (0xEA63) which fixed this issue until the next device with a CP2102N is installed

As it turns out, the cost of a $40 UPS is actually 10 hours of work and $61 in parts, although one cannot put a value on all the lessons learned here.

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Washington Consumers Gain Right To Repair For Cellphones And More

May 28, 2025 by Maya Posch 30 Comments

Starting January 1st, 2026, Washington state’s new Right to Repair law will come into effect. It requires manufacturers to make tools, parts and documentation available for diagnostics and repair of ‘digital electronics’, including cellphones, computers and similar appliances. The relevant House Bill 1483 was signed into law last week after years of fighting to make it a reality.

A similar bill in Oregon faced strong resistance from companies like Apple, despite backing another Right to Repair bill in California. In the case of the Washington bill, there were positive noises from the side of Google and Microsoft, proclaiming themselves and their products to be in full compliance with such consumer laws.

Of course, the devil is always in the details, with Apple in particular being a good example how to technically comply with the letter of the law, while throwing up many (financial) roadblocks for anyone interested in obtaining said tools and components. Apple’s penchant part pairing is also a significant problem when it comes to repairing devices, even if these days it’s somewhat less annoying than it used to be — assuming you’re running iOS 18 or better.

That said, we always applaud these shifts in the right direction, where devices can actually be maintained and repaired without too much fuss, rather than e.g. cellphones being just disposable items that get tossed out after two years or less.

Thanks to [Robert Piston] for the tip.

Reconditioning A Vintage CRT Tube

May 27, 2025 by Jenny List 27 Comments

Plenty of readers will be familiar with CRT televisions, not least because many of us use them with retrocomputers and consoles. But perhaps fewer will have worked with CRTs themselves as components, and of those, fewer still will be familiar with the earlier generation of tubes. In the first few decades of color TV the tubes were so-called delta gun because their three electron guns were arranged in a triangular form. [Colorvac] has put up a video in which they demonstrate the reconditioning of one of these tubes from a late-1960s Nordmende TV.

The tube in question isn’t one of the earlier “roundies” you would find on an American color TV from the ’50s or early ’60s, instead it’s one of the first generation of rectangular (ish) screens. It’s got an under-performing blue gun, so they’re replacing the electron gun assembly. Cutting the neck of the tube, bonding a new neck extension, and sealing in a new gun assembly is not for the faint-hearted, and it’s clear they have both the specialist machinery and the experience required for the job. Finally we see the reconditioned tube put back into the chassis, and are treated to a demonstration of converging the three beams.

For those of us who cut our teeth on these devices, it’s fascinating.

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Trashed Sound System Lives To Rock Another Day

May 22, 2025 by Bryan Cockfield 6 Comments

Plenty of consumer goods, from passenger vehicles to toys to electronics, get tossed out prematurely for all kinds of reasons. Repairable damage, market trends, planned obsolescence, and bad design can all lead to an early sunset on something that might still have some useful life in it. This was certainly the case for a sound system that [Bill] found — despite a set of good speakers, the poor design of the hardware combined with some damage was enough for the owner to toss it. But [Bill] took up the challenge to get it back in working order again.

The main problem with this unit is that of design. It relies on a remote control to turn it on and operate everything, and if that breaks or is lost, the entire unit won’t even power on. Tracing the remote back to the control board reveals a 15-pin connector, and some other audio sleuths online have a few ways of using this port to control the system without the remote.

[Bill] found a few mistakes that needed to be corrected, and was eventually able to get an ESP8266 (and eventually an ESP32) to control the unit thanks largely to the fact that it communicates using a slightly modified I2C protocol.

There were a few pieces of physical damage to correct, too. First, the AC power cable had been cut off which was simple enough to replace, but [Bill] also found that a power connector inside the unit was loose as well. With that taken care of he has a perfectly functional and remarkably inexpensive sound system ready for movies or music. There are some other options available for getting a set of speakers blasting tunes again as well, like building the amplifier for them from scratch from the get-go.

We can see the internal pads from an integrated circuit where the epoxy has been ground away.

When Repairs Go Inside Integrated Circuits

May 20, 2025 by John Elliot V 36 Comments

What can you do if your circuit repair diagnosis indicates an open circuit within an integrated circuit (IC)? Your IC got too hot and internal wiring has come loose. You could replace the IC, sure. But what if the IC contains encryption secrets? Then you would be forced to grind back the epoxy and fix those open circuits yourself. That is, if you’re skilled enough!

In this video our hacker [YCS] fixes a Mercedes-Benz encryption chip from an electronic car key. First, the black epoxy surface is polished off, all the way back to the PCB with a very fine gradient. As the gold threads begin to be visible we need to slow down and be very careful.

The repair job is to reconnect the PCB points with the silicon body inside the chip. The PCB joints aren’t as delicate and precious as the silicon body points, those are the riskiest part. If you make a mistake with those then repair will be impossible. Then you tin the pads using solder for the PCB points and pure tin and hot air for the silicon body points.

Once that’s done you can use fine silver wire to join the points. If testing indicates success then you can complete the job with glue to hold the new wiring in place. Everything is easy when you know how!

Does repair work get more dangerous and fiddly than this? Well, sometimes.

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Studying QR Code Degradation

May 13, 2025 by Jenny List 30 Comments

It’s fair to say that QR codes are a technology that has finally come of age. A decade or more ago they were a little over-hyped and sometimes used in inappropriate or pointless ways, but now they are an accepted and useful part of life.

They’re not without their faults though, one of which is that despite four increasingly redundant levels of error correction, there comes a point at which a degraded QR code can no longer be read. [HumanQR] is soliciting these broken QR codes for research purposes and inclusion in an eventual open-source database, and they’ll even have a shot at repairing your submissions for you.

It’s a problem inherent to all digital media, that once the limit of whatever error correction they contain has been reached, they arrive at a cliff-edge at which they go immediately from readability to non readability. The example given in the linked article is a locator tag on a stray cat, it had been rubbed away in part. Improving its contrast, sharply defining its edges, and improving the definition of its fiducials was able to revive it, we hope leading to the cat being returned home.

The idea is that by studying enough damaged codes it should be possible to identify the means by which they become degraded, and perhaps come up with a way to inform some repair software. Meanwhile if you are interested, you might want to learn more about how they work, the hard way.