Repairing A Self-Destructing SRS DG535 Digital Delay Generator

January 7, 2026 by Maya Posch No comments

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.

Faraday Effects Emerging From The Optical Magnetic Field

January 6, 2026 by Maya Posch 14 Comments

As an electromagnetic radiation phenomenon, it’s perhaps not so surprising that light is affected by a magnetic field. This Faraday effect (FE) has been used since its discovery by [Michael Faraday] in 1845 for a wide range of applications, allowing for the manipulation of light’s polarization, something which is very useful in the field of optics, for remote sensing and spintronics. Despite this being such a well-known property of EM radiation a recent study claims to have made a new discovery here, with what they claim is about the ‘optical magnetic field’.

Their central claim is that it is not just the electrical component that contributes to the FE, but also the magnetic one, due to Zeeman energy that expresses itself from the magnetic component as a form of inverse FE. Based on their experimental findings they estimate that it contributes to the final measured FE by about 17% at a wavelength of 800 nm.

While definitely a very niche physics paper, and with no immediate implications, if independently confirmed it could deepen our understanding of the Faraday effect, and how to use it in future technologies.

The Many Questions And Challenges With DIY Hydroelectric Generators

January 6, 2026 by Maya Posch 58 Comments

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.

Continue reading “The Many Questions And Challenges With DIY Hydroelectric Generators” →

The Use Of Ultrasound To Take On Cancerous Tumors

January 6, 2026 by Maya Posch 31 Comments

As areas of uncontrolled cell growth, cancerous growth form a major problem for a multi-celled organism like us humans. Thus before they can begin to affect our long-term prospects of a continued existence, eradicating these cells-gone-wrong is essential. Unfortunately, doing so without affecting healthy cells significantly is tough. Treatments such as chemotherapy are correspondingly rough on the body, while radiation therapy is a lot more directed. Perhaps one of the more fascinating treatments involves ultrasound, with the IEEE Spectrum magazine recently covering one company providing histotripsy equipment.

Diagram showing how HIFU can be used to destroy tissue in the body. An acoustic lens is used to focus sound to a small point in the body. (Credit: James Ross McLaughlan, Wikimedia)

Ultrasound has found many applications in the medical field far beyond imaging, with therapeutic ultrasound by itself covering a variety of methods to perform actions within the body without breaking the skin. By using high-energy ultrasound, everything from kidney stones to fat cells and cancerous cells can be accurately targeted and destroyed. For liver tumors the application of so-called histotropsy has become quite common, allowing certain types of tumors to be ablated non-invasively after which the body can handle the clean-up.

Histotropsy is a form of high-intensify focused ultrasound (HIFU) that uses either continuous or pulsed waves to achieve the desired effect, with the HIFU transducer equipped with an acoustic lens to establish a focal point. In the case of histotripsy cavitation is induced at this focal point that ends up destroying the local tissue. Beyond liver tumors the expectation is that other tumors will soon be treated in a similar manner, which could be good news for especially solid tumors.

Along with new approaches like CAR T cell immunotherapy, the prospects for cancer becoming a very treatable set of diseases would seem to be brighter than ever.

How Advanced Autopilots Make Airplanes Safer When Humans Go AWOL

January 6, 2026 by Maya Posch 21 Comments

It’s a cliché in movies that whenever an airplane’s pilots are incapacitated, some distraught crew member queries the self-loading freight if any of them know how to fly a plane. For small airplanes we picture a hapless passenger taking over the controls so that a heroic traffic controller can talk them through the landing procedure and save the day.

Back in reality, there have been zero cases of large airliners being controlled by passengers in this fashion, while it has happened a few times in small craft, but with variable results. And in each of these cases, another person in the two- to six-seater aircraft was present to take over from the pilot, which may not always be the case.

To provide a more reliable backup, a range of automated systems have been proposed and implemented. Recently, the Garmin Emergency Autoland system got its first real use: the Beechcraft B200 Super King Air landed safely with two conscious pilots on board, but they let the Autoland do it’s thing due to the “complexity” of the situation.

Continue reading “How Advanced Autopilots Make Airplanes Safer When Humans Go AWOL” →

Powering On A 1985 Photophone CP220 Videoconference System

January 6, 2026 by Maya Posch 9 Comments

The concept of remote video calls has been worked on since Bell’s phone company began pitching upgrading from telegrams to real-time voice calls. It wasn’t until the era of digital video and real-time video compression that commercial solutions became feasible, with the 1985 Image Data Corporation Photophone CP220 being an early example. The CP220 is also exceedingly rare due to costing around $25,000 USD when adjusted to inflation. This makes the teardown and repair on the [SpaceTime Junction] channel a rather unique experience.

Perhaps the coolest part of the device is that the manual is integrated into the firmware, allowing you to browse through it on the monochrome CRT. Unfortunately after working fine for a while the device released the magic smoke, courtesy of the usual Rifa capacitors doing their thing. This is why a full teardown was necessary, resulting in the PSU being dug out and having said capacitors swapped.

After this deal the device powered on again, happily accepting a video input and saving screenshots to the floppy drive before it was replaced with a FDD emulator running FlashFloppy firmware. Unfortunately no video call was attempted, probably because of the missing camera and having to set up a suitable POTS landline for the built-in modem. Hopefully we’ll see that in an upcoming video to see what we common folk were missing out on back in the day.

Continue reading “Powering On A 1985 Photophone CP220 Videoconference System” →

Close-Up Look Reveals That Raindrops Are More Erosive Than Assumed

January 5, 2026 by Maya Posch 18 Comments

Whenever it rains, people generally don’t look too closely at what the drops do exactly when they hit a surface. We generally assume that stuff will get wet and depending on the slope of the surface it’ll run off downhill at some point, probably in a nice, neat flow. Of course, reality doesn’t work that way, as Swiss researchers recently found when they pointed high-speed cameras at simulated raindrops. Their findings were published recently in Applied Physical Sciences, which is sadly paywalled, but the summary article over at phys.org provides some details, including a video.

The researchers set up a 1.2 meter long dry silicate sand surface with a 30° slope on which the drops were released. In the top image you can see two stills of the result, with the full video showing the drops turning into either peanut- or doughnut-shaped forms that gathered significant amounts of sand grains. These grains mix with the water, allowing a single drop to erode significant amounts of material from a slope, more than was previously assumed in existing soil erosion models.

Beyond erosion, these findings also offer insights for similar dynamics in other fields, all thanks to a group of researchers who got curious during a rainy walk and decided to take a closer look.