Restoring A Vintage Tube Tester To Its Former Glory

It can be difficult for modern eyes to make much sense of electronics from the 1960s or earlier. Between the point-to-point soldering, oddball components, and the familiar looking passives blown up to comical proportions like rejected props from “Honey, I Shrunk the Kids”, even experienced hardware hackers may find themselves struggling to understand what a circuit is doing. But that didn’t stop [Cat0Charmer] from taking the time to lovingly restore this Hickok Cardmatic KS-15874-L2 tube tester.

The good news was that the machine had nearly all of its original parts, down to the Hickok branded tubes in the power supply. Unfortunately it looks like a few heavy handed repairs were attempted over the years, with a nest of new wires and components intermixed with what [Cat0Charmer] actually wanted to keep. The before and after shots of individual sections of the machine are particularly enlightening, though again, don’t feel to bad if you still can’t make heads or tails of the cleaned up version.

Hiding new capacitors inside of the old ones.

As you’d expect for a machine of this age, many of the original components were way out of spec. Naturally the capacitors were shot, but even the carbon composition resistors were worthless after all these years; with some measuring 60% away from their original tolerances.

We particularly liked how [Cat0Charmer] hollowed out the old capacitors and installed the new modern ones inside of them, preserving the tester’s vintage look. This trick wasn’t always feasible, but where it was applied, it definitely looks better than seeing a modern capacitor adrift in a sea of 60’s hardware.

After undoing ham-fisted repairs, replacing the dud components, and installing some new old stock tubes, the tester sprung to life with renewed vigor. The previously inoperable internal neon lamps, used by the tester’s voltage regulation system, shone brightly thanks to all the ancillary repairs and changes that went on around them. With a DIY calibration cell built from the schematics in an old Navy manual, [Cat0Charmer] got the tester dialed in and ready for the next phase of its long and storied career.

We love seeing old hardware get restored. It not only keeps useful equipment out of the scrap heap, but because blending new and old technology invariably leads to the kind of innovative problem solving this community is built on.

Vintage HP-25 Calculator Gets Wireless Charging

[Jan Rychter] really likes his multiple HP-25C calculators, but the original battery pack design is crude and outdated. No problem — he whips up a replacement using Fusion 360 to design an enclosure, prints a few on his SLS 3D printer, and packs them with LiPo batteries and Qi/WPC wireless charging circuits.

In his blog post, he explains the goals and various design decisions and compromises that he made along the way. We like [Jan]’s frank honesty as he remarks on something we have all been guilty of at one time or another:

In the end, I went with design decisions which might not be optimal, but in this case (with low power requirements) provide acceptable performance. In other words, I winged it.

One problem which proved difficult to solve was how to provide a low battery indicator. Since low voltage on a LiPo is different from the original HP-25’s NiCad cells, it wasn’t straightforward, especially since [Jan] challenged himself to build this without using a microcontroller. He discovered that the HP-25’s internal low battery circuit was triggered by a voltage of 2.1 volts or lower.

In a really clever hack, [Jan] came up with the idea of using an MCU reset supervisor chip with a low voltage threshold of 3.0 volts, which corresponds with the low voltage threshold of the LiPo battery he is using. The reset signal from the supervisor chip then drives one of the pins of the TPS62740 programmable buck converter, changing its output from 2.5 volts to 2.1 volts.

This project is interesting on several levels — extending the life of a useful but end-of-life calculator, improving the original battery design and introducing new charging techniques not available in the early 1970s, and it is something that a hobbyist can afford to do in a home electronics lab. We do wonder, could such a modification could turn an HP-25 into an HP-25C?

We’ve written about battery pack replacement project before, including one for the Sony Discman and another for an electric drill. Let us know if you have any battery pack replacement success (or failure) stories in the comments below.

Spacewar! On PDP-11 Restoration

If you want to play the original Spacewar! but you don’t have a PDP-1 nearby, then you’re in luck — assuming you have a PDP-11, that is. [Mattis Lind] has successfully restored a PDP-11 port of the game from PDF scans of the source code, which was thought to have been lost to the trash bins of DECUS (Digital Equipment Computer Users’ Society). Fortunately, [Mattis] learned that [Bill Seiler], one of the original authors, had saved a printout of the assembly language. Using a combination of OCR and manual transcription to retrieve the code, [Mattis] took a deep dive into cleaning up the errors and solving a whole lot of system library and linking issues. Adding to the difficulty is that his PDP-11 is slightly different from the one used in 1974 when this port was written.

The project was not all software — [Mattis] also needed to make a pair of joysticks, which he made from a handful of items found on AliExpress. As you can see in the video below, he indeed got it all working. [Mattis] is no stranger to the PDP-11 world. We wrote about his PDP-11 restoration project back in 2015, a quest that took over 18 months.

Continue reading “Spacewar! On PDP-11 Restoration”

Original Game Boy Powered Up With GBA Motherboard

The Game Boy DMG-01 is about as iconic as a piece of consumer electronics can get, but let’s be honest, it hasn’t exactly aged well. While there’s certainly a number of games for the system that are still as entertaining in 2021 as they were in the 80s and 90s, the hardware itself is another story entirely. Having to squint at the unlit display, with its somewhat nauseating green tint, certainly takes away from the experience of hunting down Pokémon.

Which is precisely why [The Poor Student Hobbyist] decided to take an original Game Boy and replace its internals with more modern hardware in the form of a Game Boy Advance (GBA) SP motherboard and aftermarket IPS LCD panel. The backwards compatibility mode of the GBA allows him to play those classic Game Boy and Game Boy Color games from their original cartridges, while the IPS display brings them to life in a way never before possible.

Relocating the cartridge connector took several attempts.

Now on the surface, this might seem like a relatively simple project. After all, the GBA SP was much smaller than its predecessors, so there should be plenty of room inside the relatively cavernous DMG-01 case for the transplanted hardware. But [The Poor Student Hobbyist] made things quite a bit harder on himself by deciding early on that there would be no external signs that the Game Boy had been modified; beyond the wildly improved screen, anyway.

That meant deleting the GBA’s shoulder buttons, though since the goal was always to play older games that predated their addition to the system, that wasn’t really a problem. The GBA’s larger and wider screen is still intact, albeit hidden behind the Game Boy’s original bezel. It turns out the image isn’t exactly centered on the physical display, so [The Poor Student Hobbyist] came up with a 3D printed adapter to mount it with a slight offset. The adapter also allows the small tactile switch that controls the screen brightness to be mounted where the “Contrast” wheel used to go.

An incredible amount of thought and effort went into making the final result look as close to stock as possible, and luckily for us, [The Poor Student Hobbyist] did a phenomenal job of documenting it for others who might want to make similar modifications. Even if you’re not in the market for a rejuvenated Game Boy, it’s worth browsing through the build log to marvel at the passion that went into this project.

Some would argue [The Poor Student Hobbyist] should have just put a Raspberry Pi into a Game Boy case and be done with it, but where’s the fun in that? Sure it might have been a somewhat better Bitcoin miner, but there’s something to be said for playing classic games on real hardware.

Smashed Amiga 2000 Gets New Lease On Life

For most people, opening up a package and seeing that the Amiga 2000 you purchased on eBay had been smashed up by the delivery carrier would be a heartbreaking moment. But not [Drygol]. If you live and breathe vintage computer restorations like he does, finding your latest acquisition is in need of more repairs and upgrades than you originally anticipated is actually a bonus.

The first issue that needed sorting out was the broken case. This Amiga must have had one wild ride, as there were several nasty cracks in the front panel and whole chunks had been broken off. We’ve seen [Drygol] repair broken computer cases before, but it seems like each time he comes up with some new tricks to bring these massacred pieces of plastic back to like-new condition. In this case plastic welding is used to hold the parts together and fill in the gaps, and then brass mesh is added to the backside for strength. The joints are then sanded, filled in with polyester putty, and finally sprayed with custom color matched paint. While he was in the area, he also filled in a hole the previous owner had made for a toggle switch.

Then [Drygol] moved onto the internals. Some of the traces on the PCB had been corroded by a popped battery, a socket needed to be replaced, and as you might expect for a machine of this vintage, all of the electrolytic capacitors were suspect and needed to go. Finally, as the system didn’t have a power supply, he wired in a picoPSU. That got the 34 year old computer back up and running, and at this point, the machine was almost like new again. So naturally, it was time to start with the upgrades and modifications.

Case fan, video adapter, and picoPSU.

[Drygol] added an IDE interface and connected a CompactFlash adapter as the computer’s primary drive. For the secondary, he installed a GoTek floppy drive emulator that lets you replace a mountain of physical disks with a USB flash drive full of images. Between the two, all of the computer’s storage needs are met with nary a moving part.

The emulator was given its own 3D printed front panel to fit with the Amiga’s visual style, and he also printed out a holder for the RGB4ALL S-Video/Composite adapter installed on the rear of the machine. To help keep all this new gear cool, he finished things off with a new case fan.

Some will no doubt complain about the addition of the extra gadgetry, but to those people, we suggest you just focus on the phenomenal case restoration work. While you might not agree with all of the modifications [Drygol] makes, there’s no question that you can learn something by going through his considerable body of work.

Restored Dreamcast Is A SEGA Fan’s Dream Come True

[Bren Sutton] has been a long time fan of SEGA’s Dreamcast, eagerly snapping one up right around its October 1999 European release. But after years of neglect and a somewhat questionable paint job a decade or so back, he decided it was time to spruce his old friend up. He could have just cleaned the machine and been done with it, but he took the opportunity to revamp the console’s internals with both practical and cosmetic trickery.

The first step was getting the system looking a bit fresher. Removing the silver metallic paint he applied in his youth with a rattle can wasn’t going so well, so he ended up buying a broken donor console on eBay so he’d have a new shell to work with. The donor was yellowed with age, but a coating of peroxide cream and a few hours under a cheap UV light got it whitened up nicely. Now that he had a fresh new case, [Bren] turned his attention to the internal components.

Those who might be plugged into the active Dreamcast homebrew scene may already know that several upgrade modules exist for SEGA’s last home game console. One of the most popular replaces the optical drive with an SD card filled with your favorite game ISOs. You can also get a modern high efficiency power supply, as well as a board that replaces the original soldered-on clock battery with a slot that fits a CR2032. [Bren] threw them all in, ensuring several more years of gaming bliss.

But he wasn’t done yet. He also wanted to add some visual flair to his new and improved console. After some consideration, he gingerly cut the logo out of the Dreamcast’s lid, and installed an Adafruit CLUE board underneath it. With a few carefully crafted GIFs installed onto the CircuitPython-powered board, the console now has a gorgeous fully animated logo that you can see in the video after the break.

[Bren] could have really taken his console to the next level by doubling its available RAM to an eye-watering 32 MB, but considering the limited software support for that particularly bodacious modification, we’ll let it slide. Continue reading “Restored Dreamcast Is A SEGA Fan’s Dream Come True”

A Deep Dive Into The Chemistry Of Retrobright

Considerable effort is often required to rejuvenate the yellowed and grungy plastic cases of retrocomputing gear. One generally does well to know their enemy in order to fight it, though, which is where this guide to the chemistry of plastic yellowing and whitening (PDF) comes in handy.

“The Retrobright Mystery” was written and sent in to us by [Caden Xu], a high school student who also goes by the alias [Saltypretzel]. The paper begins with an excellent description of the chemistry of plastic yellowing. We had always heard that the yellowing in ABS, or acrylonitrile-butadiene-styrene, the plastic most commonly used for cases back in the day, was primarily caused by brominated compounds added to the plastic as flame retardants. It turns out that’s only a minor contributor, with the bulk of yellowing occurring thanks to a complex chain of reactions starting with free radicals liberated from the butadiene copolymer through a reaction requiring oxygen and energy.

Reactive radicals from the decomposing synthetic rubber, added to ABS to increase its flexibility, unroll the benzene ring in styrene copolymers to form a conjugated compound called 2-hydroxymuconic acid. The alternating double and single bonds in this compound tend to absorb light towards the blue end of the spectrum strongly, so the accumulation of 2-HMA in the plastic over time thus makes it reflect more and more yellow and red wavelengths, giving aged ABS its unhealthy bronze glow.

Luckily, just as ketchup smears and grass stains, both rich in conjugated compounds like lycopene and chlorophyll, can be bleached out of existence, so too can yellowed plastics. [Caden] notes that Retrobright, which contains a powerful dose of hydrogen peroxide, does its whitening trick by breaking the UV-absorbing double bonds in 2-HMA. There’s little that can be done about the embrittlement of the ABS caused by the breakdown of butadiene copolymers, but at least it’ll look good.

We found this guide quite comprehensive and instructive, and it should only help retrocomputing fans in their restoration efforts. For those less interested in the chemistry, [Bob Baddeley] published an overview of the yellowing of plastic and manufacturing steps to avoid it, and we covered the more practical considerations of Retrobright treatment too.