Heathkit IM-13 VTVM Repair

If you are under a certain age, you might not know the initialism VTVM. It stands for vacuum tube voltmeter. At first glance, you might just think that was shorthand for “old voltmeter” but, in fact, a VTVM filled a vital role in the old days of measuring instruments. [The Radio Mechanic] takes us inside a Heathkit IM-13 that needed some loving, and for its day it was an impressive little instrument.

Today, our meters almost always have a FET front end and probably uses a MOSFET. That means the voltage measurement probes don’t really connect to the meter at all. In a properly working MOSFET, the DC resistance between the gate and the rest of the circuit is practically infinite. It is more likely that a very large resistor (like 10 megaohms) is setting the input impedance because the gate by itself could pick up electrostatic voltage that might destroy the device. A high resistance like that is great when you make measurements because it is very unlikely to disturb the circuit you are trying to measure and it leads to more accurate measurements.

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Mystery HP Gear Teardown

What’s round, has what looks like a vacuum tube in the center, and was made in the 1950s by HP? We don’t know either, but [The Signal Path] restored one and shows us this mystery instrument in a recent video that you can see below. We aren’t going to spoil the surprise over what the device is, but we will share that he does reveal what it is very early in the video, so there’s not much of a tease.

We will, however, give you a few hints. Looking at it, you can guess that it is meant for high voltage use and, in fact, it is rated for up to 25 kV. We’ll also drop the hint that it is made for use with AC, not DC. The shape of the plug at the end of the wire is also a clue, we think.

There isn’t much inside the unusual round case (another clue, by the way), but there are some vintage parts we haven’t seen in quite awhile. One last clue: Why is there a metal rod and ball sticking out of one side of the device?

Honestly, the insides are a bit underwhelming so unlike some teardown videos we’ve seen, the real star of this video is the unusual device more so than its inner workings. If you have a hankering for a more sophisticated HP exploration, check out the HP3458A repair we covered earlier. Or go old school and peek inside an HP 150A.

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The HP3458A: King Of Multimeters For Three Decades

[Marco] looks at a lot of meters. However, he considers the HP3458A the best even though they were introduced more than 30 years earlier in 1989. Someone donated one to [Marco] but it presented some error messages on startup and exhibited erratic behavior, so he had some repairs to do.

The error codes hinted there were issues with the multislope analog to digital converter and that’s what sets the meter apart, according to [Marco]. The meter has 8.5 digits, so a normal conversion stage won’t cut it.

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Electronic Covid Test Tear Down Shows Frustrating Example Of 1-Time-Use Waste

The latest video from [TheSignalPath] is a result of his purchase of a home COVID-19 test. He found an electronic version that connects to your cell phone and displays the results on the phone. The device is an antigen test and, internally, works like the home tests that show the results using lines similar to a pregnancy test. So, somehow, the phone version reads the lines and communicates with the phone. But how? That’s the point of the video, which you can see below.

In a traditional test, there’s a control line that has to appear to show that the test was done correctly. Then a line under that indicates detection of the virus. The circuit board inside the electronic test has a plastic unit onboard that contains a similar strip and has optical sensors for both the reference line and the detection line. Since it is essentially an optical device — there are some lenses in the strip assembly that look like they are detecting the dye as it moves through the strip with LEDs onboard to shed light on the situation.

Under the microscope, the CPU is a typical Bluetooth-capable ARM chip from Nordic. The board did power up, but the device is made to only operate once because of the test strip. The video notes — and we agree — it seems wasteful to create an entire Bluetooth-enabled microcontroller board with optical components just to read a strip one time that is pretty easy to read to start with. We’ll stick with the simple test strip. Still, it is interesting to see the insides.

If you want to read more about antigen tests, we covered that. We also talked about PCR testing.

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Valve Reluctantly Shows How To Mod The Steam Deck

As the narrator in this official instructional video from Valve reminds the viewer several times, the gaming company would really rather you not open up your brand new Steam Deck and start poking around. They can’t guarantee that their software will function should you start changing the hardware, and since there’s no source for replacement parts yet anyway, there’s not much you can do in the way of repairs.

That said, Valve does believe you have the right to take apart your own device, and has produced the video below as an aid to those who are willing risk damaging their new system by opening it up. Specifically, the video goes over how to replace the most likely wear items on the handheld, namely the thumb sticks and the SSD. It seems inevitable that the stock thumb sticks will wear down after a couple years of hard use, so we’re glad to see they are easily removable modules. As for the SSD, it stands to reason that users would want to swap it out for faster and higher capacity models as they become available in the coming years.

Sooner or later, these are going to need to be replaced.

Now to be clear, we appreciate Valve making this video, and would love to see other manufacturers be so forthcoming. But we have to admit that some of its messaging does seem a bit heavy handed. The narrators admonition that users who open their Steam Deck are literally taking their lives into their own hands due to the danger of potentially rupturing the system’s lithium-ion battery is a bit hyperbolic for our tastes. The constant reminders of how badly you could bungle the job just comes off as overly preachy, though to be fair, we probably aren’t the intended audience.

Outside of its obvious gaming functions, we’re excited too see what the community can do with the Steam Deck. With official reference material like this, perhaps we’ll even start seeing some hardware modifications before too long. Though we wouldn’t blame you for hitting the Mute button halfway through.

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Sinclair Pocket TV Teardown

A pocket-sized TV is not a big deal today. But in 1983, cramming a CRT into your pocket was quite a feat. Clive Sinclair’s TV80 or FTV1 did it with a very unique CRT and [Dubious Engineering] has a teardown video to show us how it was done.

A conventional CRT has an electron gun behind the screen which is why monitors that use them are typically pretty thick. The TV80’s tube has the electron gun to the side to save space. It also uses a fresnel lens to enlarge the tiny image.

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Shortwave Radio Picks Up Sideband

With the push to having most of a radio receiver as part of a PC, it might seem odd to have a standalone communication receiver, but [OM0ET] reviews the latest one he picked up, an ATS25. Inside isn’t much: a battery, a speaker, an encoder, and a Si4732 that provides the RF muscle.

It appears the receiver is pretty broadband which could be a problem. [OM0ET] suggests adding selectivity in the antenna or adding an extra board to use as a bandpass filter.

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