Hacker Tactic: Internal ESD Diode Probing

December 14, 2023 by Arya Voronova 15 Comments

Humans are walking high voltage generators, due to all the friction with our surroundings, wide variety of synthetic clothes, and the overall ever-present static charges. Our electronics are sensitive to electrostatic discharge (ESD), and often they’re sensitive in a way most infuriating – causing spurious errors and lockups. Is there a wacky error in your design that will repeat in the next batch, or did you just accidentally zap a GPIO? You wouldn’t know until you meticulously check the design, or maybe it’s possible for you to grab another board.

Thankfully, in modern-day Western climates and with modern tech, you are not likely to encounter ESD-caused problems, but they were way more prominent back in the day. For instance, older hackers will have stories of how FETs were more sensitive, and touching the gate pin mindlessly could kill the FET you’re working with. Now, we’ve fixed this problem, in large part because we have added ESD-protective diodes inside the active components most affected.

These diodes don’t just help against ESD – they’re a general safety measure for protecting IC and transistor pins, and they also might help avoid damaging IC pins if you mix. They also might lead to funny and unexpected results, like parts of your circuit powering when you don’t expect them to! However, there’s an awesome thing that not that many hackers know — they let you debug and repair your circuits in a way you might not have imagined.

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Putting The Magic Smoke Back Into A Dodgy Spectrum Analyzer

September 12, 2023 by Dan Maloney 3 Comments

The trouble with fixing electronics is that most devices are just black boxes — literally. Tear it down, look inside, but it usually doesn’t matter — all you see are black epoxy blobs, taunting you with the fact that one or more of them are dead with no external indication of the culprit.

Sometimes, though, you get lucky, as [FeedbackLoop] did with this Rigol spectrum analyzer fix. The instrument powered up and sort of worked, but the noise floor was unacceptably high. Even before opening it up, there was clearly a problem; in general, spectrum analyzers shouldn’t rattle. Upon teardown, it was clear that someone had been inside before and got reassembly wrong, with a loose fastener and some obviously shorted components to show for it. But while the scorched remains of components made a great place to start diagnosis, it doesn’t mean the fix was going to be easy.

Figuring out the values of the nuked components required a little detective work. The blast zone seemed to once hold a couple of resistors, a capacitor, a set of PIN diodes, and a couple of tiny inductors. Also nearby were a pair of chips, sadly with the markings lasered off. With some online snooping and a little bit of common sense, [FeedbackLoop] was able to come up with plausible values for most of these — even the chips, which turned out to be HMC221 RF switches.

Cleaning up the board was a bit of a chore — the shorted components left quite a crater in the board, which was filled with CA glue, and a bunch of missing pads. This called for some SMD soldering heroics, which sadly didn’t fix the noise problem. Replacing the two RF switches and the PIN diodes seemed to fix the problem, albeit at the cost of some loss. Sometimes, good enough is good enough.

This isn’t the first time [FeedbackLoop] has gotten lucky with choice test equipment in need of repairs — this memory module transplant on a scopemeter comes to mind.

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Arbitrary Waveforms On The Cheap

August 12, 2023 by Al Williams 26 Comments

A signal generator that can produce the usual sine, square, and triangle waves is handy and has been a staple of electronic benches for decades. Being able to craft custom signals opens up new horizons, but historically, these instruments were expensive. The price has come down, though, and [Rishin Goswami] made a 5 MHz 8-bit signal generator with 131K data points of arbitrary waveform for a low price: about $20. If you want to spend a bit more, you can improve the output DAC and op amps, but even that should cost well under $100, all in.

This is one of those projects that seems easy until you start digging into it. For example, storing some points and generating signals using any microcontroller isn’t a big deal. But minimizing jitter and maximizing speed with a conventional processor is difficult. That’s why [Rishin] uses a Raspberry Pi Pico. The programmable I/O units are perfect for generating waveform data fast and reliably. You can see the project go through its paces in the video below.

The Pi streams data to an 8-bit DAC. However, it would be easy to improve resolution with a different converter. The DAC0808 also limits the instrument’s sample rate. The processor could likely go much faster if it had a DAC accommodating higher speeds.

This is just a proof-of-concept, so don’t expect fancy GUIs or the ability to import spreadsheets. You control the device from a command-line-like interface. Still, a good example of how to take advantage of the Pi’s hardware. We took a shot at a similar device nearly a decade ago. Those programmable I/O blocks are finding uses in some surprising applications.

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USB-C Cable Tester Is Compact And Affordable

August 11, 2023 by Chris Lott 32 Comments

We’ve all been bitten before by USB cables which were flaky, built for only charging, or just plain broken. With the increased conductor count and complexity of USB Type C, there are many more ways your cable can disappoint you. Over in Austria, [Peter Traunmüller] aka [petl] has designed the C2C caberQU USB C cable tester. This small PCB tester checks every wire on the cable, including the shield, and both connector orientations. He also makes a version for testing USB A to C cables (see video below the break).

Automatic cable testers are often associated with factory production, where you want to test a large quantity of cables quickly and automatically, and are priced accordingly. But this project makes it affordable and easy for anyone to test single cables in a home lab or small office.

The tester only checks for basic continuity, but that should solve a majority of USB-C cable problems. All the documentation for this tester is available on the project’s GitHub repository, including Gerbers, schematics, and mechanical details. Or if you’d rather buy one pre-made, [petl] has put them up for sale on Tindie. Continue reading “USB-C Cable Tester Is Compact And Affordable” →

The Crystal (High Voltage) Method

June 13, 2023 by Al Williams 11 Comments

Do high voltages affect the resonant frequency of a crystal? Honestly, we never thought about it, but [Joe] did and decided to risk his analyzer to find out. He started with some decidedly old-school crystals like you might have found in a 1960-era Novice rig. Since the crystal is piezoelectric, he wondered if using a high DC voltage to bend the crystal to move the frequency to create a variable crystal oscillator (sometimes called a VXO).

He created a rig to block DC away from the network analyzer and then feed voltage directly across the crystal. The voltage was from an ESD tester that provides over 1000 volts.

Getting a crystal to change much in frequency is difficult, which is why they are useful. So we weren’t surprised that even at very high voltages, the effect wasn’t very large. It did change the frequency, but it just wasn’t very much.

At one point, it looked like he might have killed the test equipment. There was a time when letting the smoke out of a network analyzer would have been a costly mistake, but these days the cost isn’t that prohibitive. In the end, this experiment probably doesn’t produce any practical results. Still, it is interesting, and we always enjoy watching anything that gives us more intuition about the behavior of circuits or, in this case, circuit elements.

If you need a refresher on crystal oscillators, we can help. There are other ways to modify a crystal’s frequency, of course.

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Own More Than One ‘Scope? You’ve Got Nothing On This Guy!

May 24, 2023 by Jenny List 18 Comments

We’re guessing that quite a few of our readers have a surprising amount of redundant test gear, and we ourselves have to admit that more than one instrument adorns our benches. But we are mere dilettantes, amateurs if you will, compared to [Volke Kloke]. He’s got 350 of them in his average American home, and we have to say, among them are some beauties.

The linked newspaper article is sometimes frustratingly light on the details, but fortunately he has a website all of his own where we can all get immersed in the details. Of particular interest is an instrument which doesn’t even have a CRT, the General Radio 338 string oscillograph used a mirror drum to catch a standing wave in a tungsten wire, but there are plenty more. Is your first ‘scope among them?

As we now live in the age of cheap digital ‘scopes, at any surplus sale you’ll see plenty of CRT-based instruments going for relative pennies. Of those, the more recent and high-end ones are still extremely useful instruments, and it’s not just misty-eyed reminiscing to say that they remain a worthy addition to any bench.

Want to know about early ‘scope tech? We’ve taken a look before.

A Tale Of Two Pulse Modulators

May 8, 2023 by Al Williams 7 Comments

In the realm of test equipment, there are a number of items that you don’t know you need until you need one. That’s probably the case with the HP11720A pulse modulator. [Tom] acquired two of these even though, by his own admission, he had “no need for these things.” We’d like to say we don’t get that, but — alas — we do.

The good news, though, is he used one of them to measure the quality of some coax cable and shared the exercise with us in the post and a video, which you can watch below. The device can generate pulses with extremely fast rise and fall times (under 10 nanoseconds) at frequencies from 2 to 18 GHz. These were often used in pulsed radar applications and probably cost quite a bit more new than [Tom] shelled out for them.

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