A Tricky Commodore PET Repair And A Lesson About Assumptions

April 14, 2025 by Maya Posch 11 Comments

The PET opened, showing the motherboard. (Credit: Ken Shirriff)

An unavoidable part of old home computer systems and kin like the Commodore PET is that due to the age of their components they will develop issues that go far beyond what was covered in the official repair manual, not to mention require unconventional repairs. A case in point is the 2001 series Commodore PET that [Ken Shirriff] recently repaired.

The initial diagnosis was quite straightforward: it did turn on, but only displayed random symbols on the CRT, so obviously the ICs weren’t entirely happy, but at least the power supply and the basic display routines seemed to be more or less functional. Surely this meant that only a few bad ICs and maybe a few capacitors had to be replaced, and everything would be fully functional again.

Initially two bad MOS MPS6540 ROM chips had to be replaced with 2716 EPROMs using an adapter, but this did not fix the original symptom. After a logic analyzer session three bad RAM ICs were identified, which mostly fixed the display issue, aside from a quaint 2×2 checkerboard pattern and completely bizarre behavior upon running BASIC programs.

Using the logic analyzer capture the 6502 MPU was identified as writing to the wrong addresses. Ironically, this turned out to be due to a wrong byte in one of the replacement 2716 EPROMs as the used programmer wasn’t quite capable of hitting the right programming voltage. Using a better programmer fixed this, but on the next boot another RAM IC turned out to have failed, upping the total of failed silicon to four RAM & two ROM ICs, as pictured above, and teaching the important lesson to test replacement ROMs before you stick them into a system.

The ProStar: The Portable Gaming System And Laptop From 1995

April 13, 2025 by Maya Posch 5 Comments

Whilst recently perusing the fine wares for sale at the Vintage Computer Festival East, [Action Retro] ended up adopting a 1995 ProStar laptop. Unlike most laptops of the era, however, this one didn’t just have the typical trackpad and clicky mouse buttons, but also a D-pad and four suspiciously game controller looking buttons. This makes it rather like the 2002 Sony VAIO PCG-U subnotebook, or the 2018 GPD Win 2, except that inexplicably the manufacturer has opted to put these (serial-connected) game controls on the laptop’s palm rest.

Though branded ProStar, this laptop was manufactured by Clevo, who to this day produces generic laptops that are rebranded by everyone & their dog. This particular laptop is your typical (120 MHz) Pentium-based unit, with two additional PCBs for the D-pad and buttons wired into the mainboard.

Unlike the sleek and elegant VAIO PCG-U and successors, this Clevo laptop is a veritable brick, as was typical for the era, which makes the ergonomics of the game controls truly questionable. Although the controls totally work, as demonstrated in the video, you won’t be holding the laptop, meaning that using the D-pad with your thumb is basically impossible unless you perch the laptop on a stand.

We’re not sure what the Clevo designers were thinking when they dreamed up this beauty, but it definitely makes this laptop stand out from the crowd. As would you, if you were using this as a portable gaming system back in the late 90s.

Our own [Adam Fabio] was at VCF East this year as well, and was impressed by an expansive exhibit dedicated to Windows 95.

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Repairing Classic Sound Cards

April 12, 2025 by Jenny List 15 Comments

Sound hardware has been built into PC motherboards for so long now it’s difficult to remember the days when a sound card was an expensive add-on peripheral. By the mid to late 1990s they were affordable and ubiquitous enough to be everywhere, but three decades later some of them are starting to fail. [Necroware] takes us through the repair of a couple of Creative Labs Sound Blaster 16s, which were the card to have back then.

The video below is a relaxed look at typical problems afflicting second-hand cards with uncertain pasts. There’s a broken PCB trace on the first one, which receives a neat repair. The second one has a lot more wrong with it though, and reveals some surprises. We would have found the dead 74 series chips, but we’re not so sure we’d have immediately suspected a resistor network as the culprit.

Watching these cards become sought-after in the 2020s is a little painful for those of us who were there at the time, because it’s certain we won’t be the only ones who cleared out a pile of old ISA cards back in the 2000s. If you find one today and don’t have an ISA slot, worry not, because you can still interface it via your LPC bus.

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The Jupiter Ace Remembered

April 11, 2025 by Al Williams 11 Comments

It is hard to imagine that it has been more than four decades since two of the original designers of the Sinclair ZX Spectrum broke off to market the Jupiter Ace. [Nemanja Trifunovic] remembers the tiny computer in a recent post, and we always love to recall the old computers that used TVs for screens and audio tape recorders for mass storage.

One thing we always loved about the Jupiter Ace is that while most computers of the era had Basic as their native tongue, the Ace used Forth. As the post points out, while this may have given it great geek cred, it didn’t do much for sales, and the little machine was history within a year. However, the post also proposes that Forth wasn’t the real reason for the machine’s lack of commercial success.

Why did they pick Forth? Why not? It is efficient and interactive. The only real disadvantage was that Basic was more familiar to more people. Books and magazines of the day showed Basic, not Forth. But, according to the post, the real reason for its early demise was that it was already using outdated hardware from day one.

The Ace provided only 3K of RAM and did not offer color graphics. While this may sound laughable today, it wasn’t totally out of the question in 1978. Unfortunately, the Ace debuted in 1982. There were options that offered much more for just a little less. There is also the argument that as users became less technical, they just wanted to load pre-programmed tapes or cartridges and didn’t really care what language was running the computer.

Maybe, but we did and we can’t help but imagine a future where Forth was the language of choice for personal computers. Given how few of these were made, we see a lot of projects around them or, at least, replicas. Of course, these days that can be as simple as a single chip.

A New Mechanical Keyboard For An Old Computer

April 10, 2025 by Bryan Cockfield 9 Comments

As computers age, a dedicated few work towards keeping some of the more interesting ones running. This is often a losing battle of sorts, as the relentless march of time comes for us all, human and machine alike. So as fewer and fewer of these machines remain new methods are needed to keep them running as best they can. [CallousCoder] demonstrates a way of building up a new keyboard for a Commodore 64 which both preserves the original look and feel of the retro computer but also adds some modern touches.

One of the main design differences between many computers of the 80s and modern computers is that the keyboard was often built in to the case of the computer itself. For this project, that means a custom 3D printed plate that can attach to the points where the original keyboard would have been mounted inside the case of the Commodore. [CallousCoder] is using a print from [Wolfgang] to get this done, and with the plate printed and a PCB for the keys it was time to start soldering. The keyboard uses modern switches and assembles like most modern keyboards do, with the exception of the unique layout for some of the C64 keys including a latching shift key, is fairly recognizable for anyone who has put together a mechanical keyboard before.

[CallousCoder] is using the original keycaps from a Commodore 64, so there is an additional step of adding a small adapter between the new switches and the old keycaps. But with that done and some amount of configuring, he has a modern keyboard that looks like the original. If you’re more a fan of the original hardware, though, you can always take an original C64 keyboard and convert it to USB to use it on your modern machines instead.

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ASCII To Mainframe

April 8, 2025 by Al Williams 11 Comments

IBM mainframes are known for very unusual terminals. But IBM made many different things, including the IBM 3151 ASCII terminal, which uses a cartridge to emulate a VT220 terminal. [Norbert Keher] has one and explains in great detail how to connect it to a mainframe.

It had the 3151 personality cartridge for emulating multiple IBM and DEC terminals. However, the terminal would not start until he unplugged it. The old CRT was burned in with messages from an IBM 3745, which helped him work out some of the configuration.

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The Computers Of EPCOT

April 8, 2025 by Al Williams 8 Comments

Even if you aren’t a Disney fan, you probably know about EPCOT — Experimental Prototype Community of Tomorrow — a Disney attraction that promised a glimpse of the future. [ErnieTech] takes a glimpse at the UNIVAC computer that ran the operation in the 1980s. A lot of schools had UNIVAC 1100-series computers back in those days, so while you don’t hear as much about them as, say, IBM 360s, there are hordes of people who have used the 1100s, even if they don’t remember it.

EPCOT opened in 1982, and the UNIVAC not only ran the attraction but was also visible as part of the exhibit’s ambiance. They even used the Pepper’s Ghost illusion to superimpose a little man on top of the equipment.

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