Korean Multifunction Counter Teardown

July 7, 2024 by Al Williams 5 Comments

[Thomas Scherrer] likes to tear down old test equipment, and often, we remember the devices he opens up or — at least — we’ve heard of them. However, this time, he’s got a Hung Chang HC-F100 multifunction counter, which is a vintage 1986 instrument that can reach 100 MHz.

Inside, the product is clearly a child of its time period. There’s a transformer for the linear supply, through-hole components, and an Intersil frequency counter on a chip. Everything is easy to get to and large enough to see.

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Everyone Needs A 1950s Signal Generator In Their Life

July 2, 2024 by Jenny List 8 Comments

At Hackaday, we comb the world of tech in search of good things to bring you. Today’s search brought up something very familiar, [Jazzy Jane] has an Advance E1 tube signal generator, the same model as the unit on the shelf above where this is being written. It’s new to her, so she’s giving it a teardown and fixing any safety issues before powering it on.

For a 70+ year old unit, the quality of these instruments was such that they remain useful and reliable to this day. Unsurprisingly a few things need looking at, such as an aged mains lead and a pair of filter caps in the power supply which haven’t aged well. These parts failed on the E1 here too, and while she’s taking the time to order appropriate replacements we have to admit to being cheapskates and robbing parts with an appropriate working voltage for ours from a nearby PC power supply.

Where this one becomes rather interesting is in an extra switch and socket. It’s a wafer switch with a load of capacitors, and the best guess is it provides some adjustability for the inbuilt audio oscillator which had a fixed frequency on stock models. This is part one of a series though, so we’re looking forward to finding out its purpose in the next installment. Take a look at the video below the break, and if that’s not enough, we seem to have had more than one piece of vintage British test equipment here of late.

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A Vintage AC Bridge Teardown

June 30, 2024 by Jenny List 2 Comments

If you ever encounter a British engineer of a certain age, the chances are that even if they use a modern DMM they’ll have a big boxy multimeter in their possession. This is the famous Avo 8, in its day the analogue multimeter to have. Of course it wasn’t the only AVO product, and [Thomas Scherrer OZ2CPU] is here with another black box sporting an AVO logo. This one’s an AC bridge, one of a series of models manufactured from the 1930s through to the late 1940s, and he treats us to a teardown and restoration of it.

Most readers will probably be familiar with the operation of a DC Wheatstone Bridge in which two resistances can be compared, and an AC bridge is the same idea but using an AC source. A component under test is attached to one set of terminals while one with a known value is put on the other, and the device can then be adjusted for a minimum reading on its meter to achieve a state of balance. The amount by which it is adjusted can then be used as a measure of the difference between the two parts, and thus the value of an unknown part can be deduced.

In the case of this AVO the AC is the 50Hz (remembering that this is a British instrument) mains frequency, and the reading from the bridge is taken via a single tube amplifier to a rectifier circuit and the meter. Inside it’s a treasure trove of vintage parts with an electrolytic capacitor that looks as though it might not be original, with a selenium rectifier and a copper oxide signal diode in particular catching our eye. This last part is responsible for some reading anomalies, but after cleaning and lubricating all the switches and bringing up the voltage gently, he’s rewarded with a working bridge. You can see the whole story in the video below the break.

Test equipment from this era is huge, so perhaps not all of you have the space for something like this. Some of us have been known to own other AVO products though.

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TDS 744A Scope Teardown Fixes Dodgy Channel

June 13, 2024 by Maya Posch 1 Comment

There are a lot of oscilloscopes from around the 1990s which are still very much desirable today, such as the Tektronix TDS 744A which [DiodesGoneWild] got his grubby mitts on. This is a 500 MHz, 4-channel scope, with a capture rate of 500 MS/s (4 channels) to 2 GS/s (1 channel). It also has a color display and even comes with a high-density (1.44 MB) floppy drive. Unfortunately this particular unit was having trouble with its fourth channel, and its NuColor display had degraded, something that’s all too common with this type of hybrid CRT/LCD (LCCS) technology.

Starting with a teardown of the unit to inspect the guts, there was no obvious damage on the PCBs, nor on the acquisition board which would explain the weird DC offset on the fourth channel. After cleaning and inspecting the capture module and putting the unit back together, the bias seen on channel four seemed to disappear. A reminder that the best problems are the ones that solve themselves. As for the NuColor display, this uses a monochrome CRT (which works fine) and an LCD with color filters. It’s the latter which seems degraded on this unit, with a repair still being planned.

We covered NuColor-based devices before, which offer super-sharp details that are hard to capture even with modern-day LCDs, never mind the ones of the 90s. Fixing these NuColor displays can be easy-ish sometimes, as [JVG] found when tearing apart a very similar Tektronix TDX-524A which required a power supply fix and the removal of goopy gel between the CRT and LCD to restore it.

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Schematic of the Pi Pico wireup, showing the various outputs that the firmware will generate on the GPIOs

A Scope Test Tool You Can Build With Just A Pico

May 31, 2024 by Arya Voronova 24 Comments

Ever wanted to see how well your oscilloscope adheres to its stated capabilities? What if you buy a new scope and need a quick way to test it lest one of its channels its broken, like [Paul Wasserman] had happen to him? Now you only need a Pi Pico and a few extra components to make a scope test board with a large variety of signals it can output, thanks to [Paul]’s Sig Gen Pi Pico firmware.

Despite the name it’s not a signal generator as we know it, as it’s not flexible in the signals it generates. Instead, it creates a dozen signals at more or less the same time — from square waves of various frequencies and duty cycles, to a PWM-driven DAC driving eight different waveforms, to Manchester-encoded data I2C/SPI/UART transfers for all your protocol decoder testing.

Everything is open source under the BSD 3-Clause license, and there’s even two PDFs with documentation and a user manual, not to mention the waveform screenshots for your own reference.

It’s seriously impressive how many features [Paul] has fit into a single firmware. Thanks to his work, whenever you have some test equipment in need of being tested, just grab your Pico and a few passive components.

Non Contact Scope Probe Costs Nearly Nothing

May 6, 2024 by Al Williams 2 Comments

[IMSAI Guy] wants you to build a non-contact scope probe. The cost? Assuming you have a bit of wire and a regular scope probe, it won’t cost you anything. Why do you want such a thing? You can see what he does with it in the video below.

The probe is really just a coil with little slip-over coils that grab it. You can stick it on and remove it just as easily, so you don’t have to sacrifice the probe for normal use. It won’t give you high-accuracy readings, but if you want to sniff around a circuit without directly connecting to it, it will do the trick. If you are too lazy to make a coil, you can even clip a ground lead to the probe tip, although that won’t work quite as well.

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80s Function Generator Is Both Beauty And Beast

April 23, 2024 by Tom Nardi 13 Comments

You know how the saying goes — they don’t make them like this anymore. It’s arguably true of pretty much any electronic device given the way technology changes over time, though whether or not it’s objectively a bad thing is going to vary from case to case.

As a practical example, take a look at the insides of this 80’s vintage HP 3314A function generator shared on the EEV Blog Forum by [D Straney].

With multiple PCBs stacked on top of each other, it’s hard to imagine that more components could possibly be crammed into it. One board in particular appears to be an entire Motorola 6800 computer, something which today would likely be replaced with a single microcontroller.

Which is actually why [D Straney] shared this with us in the first place. After seeing our recent post about a modern waveform generator that’s basically an empty box thanks to its modern components, they thought this would be a nice example of the opposite extreme.

So, is it a good or a bad thing that test equipment isn’t made this way anymore? Well, it’s hard to argue with the improved capabilities, smaller footprint, and reduced cost of most modern gear. But damn is the inside of this HP 3314A gorgeous. As one of the commenters on the page put it, hardware from this era was really a work of art.