This 8-Bit Commodore PET Was Hard to Fix

Over on [Ken Shirriff]’s blog is a tricky Commodore PET repair: tracking down 6 1/2 bad chips. WARNING: contains 8-bit assembly code.

The Trinity of 1977 which started the personal computer revolution were the Apple II, the Commodore PET, and the TRS-80. In this project it’s a failing Commodore PET which is being restored.

In the video below the break you can see [Ken Shirriff] and [CuriousMarc] team up to crack this tough nut. Resolving the various issues required a whole heap of software and equipment. Most notably a Keysight DSOX3104T oscilloscope, a Retro Chip Tester Pro, an old Agilent 1670G logic analyzer (this thing is rocking a 3.5″ floppy disk drive!), an old Agilent 54622A oscilloscope (also rocking a floppy drive!), a Data I/O 29B Universal Programmer With UniPak 2 insert, and the disassembly software Ghidra.

In the end there were 6 (and a half) bad chips which needed to be discovered and then replaced. This project is a reminder that it’s nice to have the right tools for the job!

If you’re interested in the Commodore PET you might like to read A Tricky Commodore PET Repair And A Lesson About Assumptions or Tracking Satellites With A Commodore PET.

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hackaday.com/2026/01/06/this-8…

How Do PAL and NTSC Really Work?

Many projects on these pages do clever things with video. Whether it’s digital or analogue, it’s certain our community can push a humble microcontroller to the limit of its capability. But sometimes the terminology is a little casually applied, and in particular with video there’s an obvious example. We say “PAL”, or “NTSC” to refer to any composite video signal, and perhaps it’s time to delve beyond that into the colour systems those letters convey.

Know Your Sub-carriers From Your Sync Pulses

A close-up on a single line of composite video from a Raspberry Pi.

A video system of the type we’re used to is dot-sequential. It splits an image into pixels and transmits them sequentially, pixel by pixel and line by line. This is the same for an analogue video system as it is for many digital bitmap formats. In the case of a fully analogue TV system there is no individual pixel counting, instead the camera scans across each line in a continuous movement to generate an analogue waveform representing the intensity of light. If you add in a synchronisation pulse at the end of each line and another at the end of each frame you have a video signal.

But crucially it’s not a composite video signal, because it contains only luminance information. It’s a black-and-white image. The first broadcast TV systems as for example the British 405 line and American 525 line systems worked in exactly this way, with the addition of a separate carrier for their accompanying sound.

The story of the NTSC colour TV standard’s gestation in the late 1940s is well known, and the scale of their achievement remains impressive today. NTSC, and PAL after it, are both compatible standards, which means they transmit the colour information alongside that black-and-white video, such that it doesn’t interfere with the experience of a viewer watching on a black-and-white receiver. They do this by adding a sub-carrier modulated with the colour information, at a frequency high enough to minimise its visibility on-screen. for NTSC this is 3.578MHz, while for PAL it’s 4.433MHz. These frequencies are chosen to fall between harmonics of the line frequency. It’s this combined signal which can justifiably be called composite video, and in the past we’ve descended into some of the complexities of its waveform.

It’s Your SDR’s I and Q, But Sixty Years Earlier

Block diagram of an NTSC colour decoder as found in a typical 1960s American TV set. Color TV Servicing, Buchsbaum, Walter H, 1968.

An analogue colour TV camera produces three video signals, one for each of the red, green, and blue components of the picture. Should you combine all three you arrive at that black-and-white video waveform, referred to as the luminance, or as Y. The colour information is then reduced to two further signals by computing the difference between the red and the luminance, or R-Y, and the blue and the luminance, or B-Y. These are then phase modulated as I-Q vectors onto the colour sub-carrier in the same way as happens in a software-defined radio.

At the receiver end, the decoder isolates the sub-carrier, I-Q demodulates it, and then rebuilds the R, G, and B, with a summing matrix. To successfully I-Q demodulate the sub-carrier it’s necessary to have a phase synchronised crystal oscillator, this synchronisation is achieved by sending out a short burst of the colour sub-carrier on its own at the start of the line. The decoder has a phase-locked-loop in order to perform the synchronisation.

So, Why The PAL Delay Line?

A PAL decoder module from a 1970s ITT TV. The blue component in the middle is the delay line. Mister rf, CC BY-SA 4.0.

There in a few paragraphs, is the essence of NTSC colour television. How is PAL different? In essence, PAL is NTSC, with some improvements to correct phase errors in the resulting picture. PAL stands for Phase Alternate Line, and means that the phase of those I and Q modulated signals swaps every line. The decoder is similar to an NTSC one and indeed an NTSC decoder set to that 4.433MHz sub-carrier could do a job of decoding it, but a fully-kitted out PAL decoder includes a one-line delay line to cancel out phase differences between adjacent lines. Nowadays the whole thing is done in the digital domain in an integrated circuit that probably also decodes other standards such as the French SECAM, but back in the day a PAL decoder was a foot-square analogue board covered in juicy parts highly prized by the teenage me. Since it was under a Telefunken patent there were manufacturers, in particular those from Japan, who would try to make decoders that didn’t infringe on that IP. Their usual approach was to create two NTSC decoders, one for each phase-swapped line.

So if you use “NTSC” to mean “525-line” and “PAL” to mean “625-line”, then everyone will understand what you mean. But make sure you’re including that colour sub-carrier, or you might be misleading someone.

hackaday.com/2026/01/07/how-do…

The Rise and Fall of The In-Car Fax Machines

Once upon a time, a car phone was a great way to signal to the world that you were better than everybody else. It was a clear sign that you had money to burn, and implied that other people might actually consider it valuable to talk to you from time to time.

There was, however, a way to look even more important than the boastful car phone user. You just had to rock up to the parking lot with your very own in-car fax machine.

Dial It Up

Today, the fax machine is an arcane thing only popular in backwards doctor’s offices and much of Japan. We rely on email for sending documents from person A to person B, or fill out forms via dedicated online submission systems that put our details directly in to the necessary databases automatically. The idea of printing out a document, feeding it into a fax machine, and then having it replicated as a paper version at some remote location? It’s positively anachronistic, and far more work than simply using modern digital methods instead.

In 1990, Mercedes-Benz offered a fully-stocked mobile office in the S-Class. You got a phone, fax, and computer, all ready to be deployed from the back seat. Credit: Mercedes-Benz

Back in the early 90s though, the communications landscape looked very different. If you had a company executive out on the road, the one way you might reach them would be via their cell or car phone. That was all well and good if you wanted to talk, but if you needed some documents looked over or signed, you were out of luck.

Even if your company had jumped on the e-mail bandwagon, they weren’t going to be able to get online from a random truck stop carpark for another 20 years or so. Unless… they had a fax in the car! Then, you could simply send them a document via the regular old cellular phone network, their in-car fax would spit it out, and they could go over it and get it back to you as needed.

Of course, such a communications setup was considered pretty high end, with a price tag to match. You could get car phones on a wide range of models from the 1980s onwards, but faxes came along a little later, and were reserved for the very top-of-the-line machines.

Mercedes-Benz was one of the first automakers to offer a remote fax option in 1990, but you needed to be able to afford an S-Class to get it. With that said, you got quite the setup if you invested in the Büro-Kommunikationssystem package. It worked via Germany’s C-Netz analog cellular system, and combined both a car phone and an AEG Roadfax fax machine. The phone was installed in the backrest of one of the front seats, while the fax sat in the fold-down armrest in the rear. The assumption was that if you were important enough to have a fax in the car, you were also important enough to have someone else driving for you. You also got an AEG Olyport 40/20 laptop integrated into the back of the front seats, and it could even print to the fax machine or send data via the C-Netz connection.

BMW would go on to offer faxes in high-end 7 Series and limousine models. Credit: BMW

Not to be left out, BMW would also offer fax machines on certain premium 7 Series and L7 limousine models, though availability was very market-dependent. Some would stash a fax machine in the glove box, others would integrate it into the back rest of one of the front seats. Toyota was also keen to offer such facilities in its high-end models for the Japanese market. In the mid-90s, you could purchase a Toyota Celsior or Century with a fax machine secreted in the glove box. It even came with Toyota branding!

Ultimately, the in-car fax would be a relatively short-lived option in the luxury vehicle space, for several reasons. For one thing, it only became practical to offer an in-car fax in the mid-80s, when cellular networks started rolling out across major cities around the world.

By the mid-2000s, digital cell networks were taking over, and by the end of that decade, mobile internet access was trivial. It would thus become far more practical to use e-mail rather than a paper-based fax machine jammed into a car. Beyond the march of technology, the in-car fax was never going to be a particularly common selection on the options list. Only a handful of people ever really had a real need to fax documents on the go. Compared to the car phone, which was widely useful to almost anyone, it had a much smaller install base. Fax options were never widely taken up by the market, and had all but disappeared by 2010.

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The Toyota Celsior offered a nice healthy-sized fax machine in the 1990s, but it did take up the entire glove box.

These days, you could easily recreate a car-based fax-type experience. All you’d need would be a small printer and scanner, ideally combined into a single device, and a single-board computer with a cellular data connection. This would allow you to send and receive paper documents to just about anyone with an Internet connection. However, we’ve never seen such a build in the wild, because the world simply doesn’t run on paper anymore. The in-car fax was thus a technological curio, destined only to survive for maybe a decade or so in which it had any real utility whatsoever. Such is life!

An RP2040 Powered ADS-B Receiver

If you’ve ever heard the sound of an aircraft passing overhead and looked at an online plane tracker to try and figure out what it was, then you’ve interacted with ADS-B. It’s a protocol designed to enable easier aircraft monitoring, and it just so happens you can decode it yourself with the right hardware and software — which is how [John McNelly] came to develop ADSBee, an open source ADS-B receiver based around an RP2040.

ADS-B uses on–off keying (OOK) at 1 Mbps, and operates at 1090 MHz. This might seem like a rather difficult protocol to decode on a microcontroller, but the RP2040’s PIO is up to the task. All it takes is a bit of optimization, and a some basic RF components to amplify and digitize the signals.

However, not all aircraft utilize the 1090 MHz ADS-B implementation, and instead use a related protocol called UAT. Operating at 978 MHz, a second receiver is needed for decoding UAT traffic data, which is where the CC1312 comes into play. ADSBee may even be the first open source implementation of a UAT decoder!

What’s quite impressive is the various form factors the module is available in. Ranging from small solder-down modules to weatherproof outdoor base stations, nearly every potential need for an ADS-B receiver is covered. With POE or ESP32 S3 options available, there is no shortage of networking options either!

ADSBees have been placed in numerous locations, ranging from base stations to drones. One user even built out a tiny flight display cluster complete with traffic indicators into an FPV drone.

This isn’t the first time we have seen ADS-B receivers used by drone enthusiasts, but this is certainly the most feature rich and complete receiver we have come across.

hackaday.com/2026/01/07/an-rp2…

Repairing a Self-Destructing SRS DG535 Digital Delay Generator

There’s a lot of laboratory equipment out there that the casual hobbyist will never need to use, but that doesn’t mean you wouldn’t snap it up if the price is right. That’s what happened when [Tom Verbeure] saw a 1980s digital delay generator at a flea market for $40. Not only is it an excellent way to learn something about these devices, but it also provides a fascinating opportunity to troubleshoot and hopefully fix it. Such was also the case with this Stanford Research Systems (SRS) DG535 that turned out to be not only broken, but even features an apparently previously triggered self-destruct feature.

These devices are pretty basic, with this specimen incorporating a Z80 MPU in addition to digital and analog components to provide a programmable delay with 12.5 nanosecond resolution on its output channels after the input trigger is sensed. For that reason it was little surprise that the problem with the device was with its supply rails, of which a few were dead or out of spec, along with a burned-out trace.

Where the self-destruct feature comes into play is with the use of current boosting resistors around its linear regulators. Although these provide a current boost over what the regulator can provide, their disadvantages include a tendency towards destruction whenever the load on the supply rail decreases. This could for example occur when you’re debugging an issue and leave some of the PCBs disconnected.

Unsurprisingly, this issue caused the same charred trace to reignite during [Tom]’s first repair attempt, but after working up the courage over the subsequent 18 months the second repair attempt went much better, also helped by the presence of the mostly correct original board schematics.

Ultimately the fixes were relatively modest, involving replacing a discrete diode bridge with an integrated one, fixing the -9 V rail with a bodge wire, and replacing the LCD with its busted AC-powered backlight with a modern one with a LED backlight. Fortunately running the 5 V rail at 7 V for a while seemed to have caused no readily observable damage, nor did flipping connectors because of SRS’ inconsistent ‘standards’ for its connector orientations.

Sadly, when [Tom] emailed SRS to inquire about obtaining an updated schematic for this unit — which is currently still being sold new for $4,495 — he merely got told to send his unit in for repair.

hackaday.com/2026/01/07/repair…

🔴 COLLOQUIO TECNICO
– Zero Trust
– MITRE ATT&CK
– EDR, XDR, SIEM
– “Come fermeresti un APT russo con accesso persistente?”
– “Spiegaci il tuo modello di threat hunting”

⚔️ Sangue. Sudore. PowerPoint.

🟢 LAVORO DOPO L’ASSUNZIONE
– “Puoi resettare la password di Mario?”
– “La stampante non va, è sicuramente un attacco hacker”
– “Apri questo PDF arrivato da un dominio .ru, è urgente”
– “Ah, noi non facciamo patching in produzione”

🧸 Costruire castelli… sul legacy.

💀 Benvenuto nella cybersecurity reale, quella italiana!

Dove difendi infrastrutture critiche
…con budget da giocattoli
…e policy scritte nel 2009.

Quindi, siate seri

#redhotcyber #cybersecurity #hacking #hacker #infosec #infosecurity #quotes #meme #comica #vignette #citazioni #cybersec #sicurezzainformatica #malware #awareness #meme #memetime

The Many Questions and Challenges with DIY Hydroelectric Generators

The concept of building your own hydroelectric generator seems simple at face value: use gravity to impart as much force as possible onto a turbine, which spins a generator, thus generating electricity. If you’re like the bloke over at [FarmCraft101] trying to DIY this with your farm pond and a lot of PVC pipes, you may have some significantly more in-depth questions, especially pertaining to what kind of generator to use. This and other questions, some of which were raised after the previous video in which the first prototype generator was assembled, are answered in this follow-up video.

When you DIY such a hydroelectric system, you have a number of options when it comes to just the turbine design alone, with the Kaplan-style turbine being one of the most straightforward ones – especially if you use a fixed pitch instead of adjustable – but you can go pretty far in the weeds with alternatives. As for the sharp drop-off after the turbine in the used design, the technical term is a draft tube, which is actually more efficient in this kind of low head, high flow hydroelectric dam situation.

After getting his money back for the unusable ‘3 kW’ generator, there were three options left: try an EBay special, get a purpose-built one from a US company, or rewind an alternator stator for higher voltage output than the standard 12/24V. Ultimately option four was chosen, as in ‘all of the above’, so that comparison is coming up in a future video.

There were also questions from viewers about why he opted to rectify the AC power from the generator and use DC transmission to the nearest farm building. The main reason is efficiency, as DC transmission lines lack the skin effect losses. The other is that the grid-tie inverter that he plans to use needs DC input anyway. Not having to deal with AC transmission issues like losses and reactive power shenanigans is a major plus here.

Once the three new generator versions are being tested it will be interesting to see how they perform. One thing with the Kaplan-style turbine is that too fast RPM induces cavitation, which will erode the propeller pretty quickly. Generally car alternators require a pretty fast RPM, so that may not work out too well. There is also the question of the DC voltage generated, as for DC transmission you want to have as high a voltage as possible to reduce the current.

The purpose-built generator he purchased tops out at 48V, which is quite low. The goal is to have at least 230 VAC before rectification, so a step-up transformer may be needed. Unfortunately three-phase transformers are pretty pricy again, making the rewound alternator seem less crazy. The wild card here is perhaps whether the EBay-purchased generator is a diamond in the rough and works out of the box as hoped.

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hackaday.com/2026/01/06/the-ma…