Xerox Alto CRTs Needed a Tiny Lightbulb to Function

In the real world, components don’t work like we imagine they do. Wires have resistance, resistors have inductance, and capacitors have resistance. However, some designers like to take advantage of those imperfections, something our old friend [Ken Shirriff] noted when he was restoring the CRT of a Xerox Alto.

[Ken] tried to connect a Xerox monitor to the Alto and — since it was almost as old as the Alto — he wasn’t surprised that it didn’t work. What did surprise him, though, is that when he turned the monitor off, a perfect picture appeared for just a split second as the unit powered off. What could that mean?

Keep in mind this is a CRT device. So a perfect picture means you have vertical and horizontal sweep all at the right frequency. It also means you have high voltage and drive on the electron guns. If you are too young to remember all that, [Ken] covers the details in his post.

He found that the CRT grid voltage wasn’t present during operation. The voltage derived from the high voltage supply but, mysteriously, the high voltage was fine. There was a small lightbulb in the grid voltage circuit. A 28V device about like a flashlight bulb. It measured open and that turned out to be due to a broken lead. Repairing the broken lead to the bulb put the monitor back in operation.

On paper, a light bulb lights up when you put current through it. In real life, it is a bit more complicated. An incandescent filament starts off as almost a dead short and draws a lot of current for a very brief time. As the current flows, the filament gets hot and the resistance goes up. That reduces the current draw. This effect — known as inrush current — is the scourge of designers trying to turn on light bulbs with transistors or other electronic switches.

However, the unknown Xerox power supply designer used that effect as a current limiter. The short 600V pulses would hardly notice the light bulb but if too much current or time elapsed, the resistance of the bulb would rise preventing too much current from flowing for too long. With the bulb open, the negative brightness grid provided an impassible barrier to the electrons. Apparently, the brightness grid lost power a bit earlier than the rest of the circuit and with it out of the way — or perhaps, partially out of the way — the picture was fine until the rest of the circuit also lost power.

We looked at [Ken’s] efforts on this machine earlier this year. Light bulbs, by the way, aren’t the only thing that changes resistance in response to some stimulus. You might enjoy the 1972 commercial from Xerox touting the Alto’s ability to do advanced tasks like e-mail and printing.

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Get Down to the Die Level with this Internal Chip Repair

Usually, repairing a device entails replacing a defective IC with a new one. But if you’ve got young eyes and haven’t had caffeine in a week, you can also repair a defective chip package rather than replace it.

There’s no description of the incident that resulted in the pins of the QFP chip being ablated, but it looks like a physical insult like a tool dropped on the pins. [rasminoj]’s repair consisted of carefully grinding away the epoxy cap to expose the internal traces leading away from the die and soldering a flexible cable with the same pitch between the die and the PCB pads.

This isn’t just about [rasminoj]’s next-level soldering skills, although we’ll admit you’ve got to be pretty handy with a Hakko to get the results shown here. What we’re impressed with is the wherewithal to attempt a repair that requires digging into the chip casing in the first place. Most service techs would order a new board, or at best solder in a new chip. But given that the chip sports a Fanuc logo, our bet is that it’s a custom chip that would be unreasonably expensive to replace, if it’s even still in production. Where there’s a skill, there’s a way.

Need more die-level repairs? Check out this iPhone CPU repair, or this repair on a laser-decapped chip.

[via r/electronics]

Space Technology and Audio Tape to Store Art

[Blaine Murphy] has set out to store an archive of visual art on cassette tape. To do so he encodes images via Slow-Scan Television (SSTV), an analogue technology from the late 50s which encodes images in for radio transmission. If you are thinking ‘space race’ you are spot on, the first images of the far side of the moon reached us via SSTV and were transmitted by the soviet Luna 3 spacecraft.

Yes, this happened

Encoding images with 5os technology is only one part of this ongoing project. Storage and playback are handled by a 90s tape deck and the display unit is a contemporary Android phone. Combining several generations in one build comes with its own set of challenges, such as getting a working audio connection between the phone and the tape deck or repairing old consumer electronics. His project logs on this topic are solid contenders for ‘Fail Of The Week’ posts. For instance, making his own belts for the cassette deck was fascinating but a dead end.

The technological breadth of the project makes it more interesting with every turn. Set some time aside this weekend for an entertaining read.

Just a couple of years back ham radio operators had the opportunity to decode SSTV beamed down from the ISS when they commemorated [Yuri Gagarin’s] birthday. Now if the mechanical part of this project is what caught your interest, you’ll also want to look back on this MIDI sampler which used multiple cassette players.

Fix Everything and Get Your Own Flailing Arms Tube Man

The staple of used car dealerships that prompted Houston to ban all ‘attention getting devices’ is called an ‘air dancer’ and was invented in 1996. And now you can build your own, even if until now the space requirements kept you from doing so.

[dina Amin] shows how to make one from a bunch of discarded hair dryers and stuff everybody is likely to find in his or her workshop. While the build as such is rather basic — these things are really simple devices after all — [dina Amin]’s project video takes us through the interesting detours that turn a build into a project. It touches on the topics of painting plastics, hardware repairs, diagnosing and fixing DC motors, and how hair dryers actually work. As an added bonus we get a good-looking solution for fixing that enclosure with the worn out threads. All that in five minutes flat.

And while you might not know if you need one, [dina Amin]’s wacky waving inflatable arm flailing arm tube man is pretty much guaranteed to work. Unlike this one.

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A Bit Of Mainstream Coverage For The Right To Repair

Here at Hackaday, we write for a community of readers who are inquisitive about the technology surrounding them. You wouldn’t be here if you had never taken a screwdriver to a piece of equipment to see what makes it work. We know that as well as delving inside and modifying devices being core to the hardware hacker mindset, so is repairing. If something we own breaks, we try to work out why it broke, and what we can do to fix it.

Unfortunately, we live in an age in which fixing the things we own is becoming ever harder. Manufacturers either want to sell us now hardware rather than see us repair what breaks, or wish to exercise total control over the maintenance of their products. They make them physically impossible to repair, for example by gluing together a cellphone, or they lock down easy-to-repair items with restrictive software, for example tractors upon which every replacement part must be logged on a central computer.

This has been a huge issue in our community for a long time now, but to the Man In The Street it barely matters. To the people who matter, those who could change or influence the situation, it’s not even on the radar. Which makes a piece in the British high-end weekly newspaper The Economist particularly interesting. Entitled “A ‘right to repair’ movement tools up“, it lays out the issues and introduces the Repair Association, a political lobby group that campaigns for “Right to repair” laws in the individual states of the USA.

You might now be asking why this is important, why are we telling you something you already know? The answer lies in the publication in which it appears. The Economist is aimed at politicians and influencers worldwide. In other words, when we here at Hackaday talk about the right to repair, we’re preaching to the choir. When they do it at the Economist, they’re preaching to the crowd who can make a difference. And that’s important.

You may recognise the tractors mentioned earlier as the iconic green-and-yellow John Deere. We’ve written about their DRM before.

Neon sign, All Electronics Service, Portland, Visitor7 [CC BY-SA 3.0].

LEGO Components Under X-Ray

[Nico71] works for a company that makes industrial CT scanners. These x-ray machines look inside a piece of equipment, allowing operators to verify assembly and to inspect for material integrity. It also allowed [Nico71] the opportunity to scan a LEGO servo he had lying around, and which no longer worked. The resulting images look fantastic, and really allow you to look into a closed system and pick apart how it works or why it’s not working. In this case, you can see one of the wires has been damaged.

[Nico71] plans to scan a bunch of LEGO components, comparing (for instance) official LEGO products with shanzhai knockoffs. Which is better constructed? It’s one thing to have thinner or cheaper plastic, or a lower grade of steel, but how is the part engineered?

We’ve covered a surprising amount of CT goodness on Hackaday, including this process for turning a CT scan into a 3D print and a post on improving a homebrew CT scanner. Continue reading “LEGO Components Under X-Ray”

Teletype Machine Resurrected

A teleprinter is, at its heart, an automatic typewriter.  It’s electrically controlled and has some smarts to be able to decode an incoming message and has something that will move the keys.   These printers have been in use since the late 1800’s and [AethericLtd] have refurbished an old 1930’s design and given it a bit of steampunk flair.

As is common with older mechanical devices that have been sitting for extended periods of time, the first thing this machine needed was a bath. The machine was separated into its three main parts and soaked in a degreasing solvent. The keyboard was the dirtiest, so it got an overnight soak. Since little of the mechanism was electrical, most of it could be submerged which helped with the cleaning.

The next step in the restoration was lubrication. In order to do a proper job, the manuals (which were available online) were consulted and synthetic motor oil used for lubrication. Once all the hundreds of parts were oiled, [AethericLtd] started working on the wiring. The original wiring in this machine was called Deltabeston – a type of wire by General Electric which uses asbestos insulation. To play it safe, that wire was left alone. The selector magnet required only 4 volts to pull up, but 4 volts wasn’t enough to run the machine. The power supply used was a 120 VDC, 200 mA supply through a 2 KΩ, 10 W resistor.

Once everything was back together and working, [AethericLtd] could take machine out and show it off. The website describes not only the restoration process but also the setup, how to connect to the machine and how to communicate with the machine. Great work! If you are interested in these machines, there have been a few Teleprinter projects on the site before: this one has been modified to connect to a modern modem, and this one prints out tweets.

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