When the chance arrived to buy a mechanical keyboard for not a lot, naturally, [Hales] jumped at it. Then it started having odd intermittent problems with some keys appearing stuck, which led to a teardown and some fault finding. The culprit was a white LED — but why this was the case is a fascinating story.
Stripping it down there didn’t seem to be an obvious culprit, but eventually, the trail led to a lack of diodes in the matrix. This keyboard had an extremely clever yet rather cursed design in which it used LEDs as both illumination and as a diode in the keyboard matrix circuit, and the faulty LED had a reverse breakdown condition that could be triggered under certain operational conditions.
More unexpectedly, it would sometimes hold on to its reverse breakdown state even after power off. Just when you think you understand a component’s properties, there’s always room for surprise. And we can safely say we’ve learned something about the design of cheaper keyboards in reading the account. It’s clear that when it comes to ‘boards, it’s best to take no chances.
Many of us will have found dusty forgotten pieces of electronics and nursed them back to health, but we were captivated by [Don]’s tale of electronic revival. Instead of perhaps a forgotten computer or television, his barn find was a Heathkit linear amplifier for radio amateurs. In that huge box underneath an impressive layer of grime were a pair of huge tubes, along with all the power supply components to give them the 2 kV they need. It should have been good for a kilowatt when new, can it be made to go on air again?
Perhaps understandably with such an old device, after cleaning away the dust of ages he replaced the power supply circuitry with new parts and PCBs. A linear amplifier is surprisingly simple, but because of the voltages and power concerned there’s a need to treat its power circuits with respect. On first power-up the filaments work and the rails come up, so when given some RF drive it comes alive. Coupled with a case restoration you’d never know how dreadful a state it had been in.
The microcomputer revolution of the 1970s and 1980s turned computers from expensive machines aimed at professionals into consumer products found in the average household. But there always remained a market for professional users, who bought equipment that was so far ahead of consumer gear it seemed to belong in a different decade. While a home computer enthusiast in 1981 might fork out a few hundred dollars for an 8-bit machine with 64 KB of memory, a professional could already buy a 32-bit workstation with 2.8 megabytes of RAM for the price of a brand-new sports car. [Tech Tangents] got his hands on one of those machines, an HP Series 200 9863C from 1981, and managed to get it up and running.
The machine came in more-or-less working condition. The display cable turned out to be dodgy, but since it was just a straight-through sub-D cable it was easily replaced. Similarly, the two 5.25″ floppy drives were standard Tandon TM100-2As which [Tech Tangents] had some experience in repairing, although these specific units merely needed a thorough cleaning to remove forty years’ worth of dust. Continue reading “Repairing A $25,000 HP Workstation To Run Pac-Man“→
We’ve heard a ton of stories over the years about abandoned technology — useful widgets, often cloud-based, that attracted an early and enthusiastic following, only to have the company behind the tech go bankrupt or decide to end operations for business reasons, which effectively bricks hundreds or perhaps millions of otherwise still-usable devices. Now imagine that happening to your brain.
[Markus Möllmann-Bohle] doesn’t have to imagine it, because he’s living it. [Markus] suffers from chronic cluster headaches, an often debilitating condition that leaves a person with intractable pain. Having lived with these headaches since 1987, and treating them with medications with varying degrees of success, [Markus] was finally delivered from his personal hell by a sphenopalatine ganglion (SPG) neuromodulator. The device consists of an unpowered stimulator implanted under the cheekbone that’s wired into the SPG, a bundle of nerves that supply the sinuses, nasal mucosa, tear glands, and many other structures in the face.
To reverse a cluster headache, [Markus] applies an external transmitter to the side of his face, which powers the implant and directs it to stimulate the SPG with low-frequency impulses, which interferes with a reflex loop that causes the symptoms associated with a cluster headache. [Markus] has been using the implant for years, but now its manufacturer has rolled up operations, leaving him with a transmitter in need of maintenance and the possibility of facing his debilitating headaches once again.
The video below shows [Markus]’s workaround, which essentially amounts to opening up the device and swapping in a new LiPo battery pack. [Markus], an electrical engineer by training, admits it’s not exactly a major hack, but it’s keeping him going for now. But he’s clearly worried because eventually, something will happen to that transmitter that’s beyond his skills to repair.
There’s cause for hope, though, as the intellectual property of the original implant company has been purchased by an outfit called Realeve, with the intention to continue support. That would be a lifesaver for [Markus] and everyone relying on this technology to live a normal life, so here’s hoping there’s no need for future hacking heroics. But as the video below details, there is a lot of neurotechnology out there, and the potential for having that bricked by a corporate decision has to be terrifying to the people who depend on them. Continue reading “Hacking Headaches: Keeping A Neurostimulator Working”→
[CuriousMarc] is back with more vintage HP hardware repair. This time it’s the HP 5245L, a digital nixie-display frequency counter from 1963. This unit is old enough to be entirely made of discrete components, but has a real trick up its sleeve, with add-on components pushing the frequency range all the way up to 18 GHz. But this poor machine was in rough shape. There were previous repair attempts, some of which had to be re-fixed with proper components. When it hit [Marc]’s shop, the oscillator was working, as well as the frequency divider, but the device wasn’t counting, and the reference frequencies weren’t testing good at the front of the machine. There were some of the usual suspects, like blown transistors. But things got really interesting when one of the boards had a couple of tarnished transistors, and a handful of nice shiny new ones — but maybe not all the right transistors. Continue reading “Do Not Attempt Disassembly: Analog Wizardry In A 1960s Counter”→
Last time we talked about a video that purported to do plastic welding, we mentioned that the process wasn’t really plastic welding as we understood it. Judging by the comments, many people agreed, but it was still an interesting technique. Now [Inventor 101] has a video about plastic repair that also talks about welding, although — again, we aren’t sure all of the techniques qualify.
That’s not to say there aren’t some clever ideas, though. There are several variations on a theme, but the basic idea is to use a bolt or something similar in a soldering iron, metal reinforcement from things like wires and staples, and donor plastic from a zip tie. While we don’t think the nylon in a typical zip tie is the best way to repair anything other than nylon, if you were repairing something 3D printed, you could easily swap out the tie for filament of the same material, which — we think — would bond better.
Having acquired some piece of old electronic equipment, be it a computer, radio, or some test gear, the temptation is there to plug it in as soon as you’ve lugged it into the ‘shop. Don’t be so hasty. Those power supplies and analog circuits often have a number of old aluminium electrolytic capacitors of unknown condition, and bad things can happen if they suddenly get powered back up again. After a visual inspection, to remove and replace any with obvious signs of leakage and corrosion, those remaining may still not be up to their job, with the oxide layers damaged over time when sat idle, they can exhibit lower than spec capacitance, voltage rating or even be a dead short circuit. [TechTangents] presents for us a guide to detecting and reforming these suspect capacitors to hopefully bring them, safely, back to service once more.
Capacitor failure modes are plentiful
When manufactured, the capacitors are slowly brought up to operating voltage, before final encapsulation, which allows the thin oxide layer to form on the anode contact plate, this is an electrically driven chemical process whereby a portion of the electrolyte is decomposed to provide the needed oxygen ions. When operating normally, with a DC bias applied to the plates, this oxidation process — referred to as ‘self-healing’ — continues slowly, maintaining the integrity of the oxide film, and slowly consuming the electrolyte, which will eventually run dry and be unable to sustain the insulating oxide layer.
If left to sit un-powered for too long, the anodic oxide layer will decay, resulting in reduced operating voltage. When powered up, the reforming process will restart, but this will be in an uncontrolled environment, resulting in a lot of excess heat and gases being vented. It all depends on how thin the oxide layer got and if holes have started to form. That is, if there is any electrolyte left to react – it may already be far too late to rescue.
If the oxide layer is sufficiently depleted, the capacitor will start to conduct, with a resultant self-heating and runaway thermal decomposition. They can explode violently, which is why there are score marks at the top of the can to act as a weak point, where the contents can burst through. A bit like that ‘egg’ scene in Aliens!
Yucky leaky capacitor. Replace these! and clean-up that conductive goo too.
The ‘safe’ way to reform old capacitors is to physically remove them from the equipment, and apply a low, controlled voltage below the rated value to keep the bias current at a low value, perhaps just 2 mA. Slowly, the voltage can be increased to push the current back up to the initial forming level, so long as the current doesn’t go too high, and the temperature is within sensible bounds. The process ends when the applied voltage is at the rated value and the current has dropped off to low leakage values.
A word of warning though, as the ESR of the reformed caps could be a little higher than design, which will result in higher operating temperature and potentially increased ripple current in power supply applications.
