Microelectronics | System Design Assembled Machines

Synopsis

I assembled two machines from hardware components that I designed over time.

I wanted two systems because I had a couple of PCBs left from each project. And second to that, I wanted to cover the entire '90s decade in terms of computing performance.

Disclaimer: I reserve the right to change these designs or implementations without further notice. These are entirely hobby do-it-yourself projects and I am not responsible for any damage made by any possible mistake in any version or revision of the schematics or PCB layouts of the computer cards involved in these projects.

This page is work in progress.
I am still adding text and images, time permits.

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Laudatur ab his, culpatur ab illis. This project consists of multiple individual sub-projects, all of them provided as-is and not for commercial purposes. It reflects my experimental work in microcomputer system design and should be treated as such. I release the schematic diagrams and circuit board layouts to the public for educational purposes. I did all this at my own expense and in my free time. If you like my work, please consider making a donation. It helps me continue these kind of projects.

Machine #01: 80386DX / 33 MHz or TX486DLC / 40 MHz

This was the dream that started it all. This is what I had in mind when I started working on all these individual x86 system design projects.

Components

This machine is made with the following components.

Known Issues

Unfortunately, there are some issues that I haven't had time to address yet.

  • Floppy disk drives do not work -- suspecting DMA problems some controllers don't work while some others do
  • Digitized sound effects do not work -- suspecting DMA problems

In the meantime, I tested multiple ISA floppy controller cards based on the Intel 82077AA or National Semiconductor PC8477BV integrated circuits. None work with this computer. The floppies will seek but will not read or write data. Every floppy access is terminated by a Drive Not Ready error. I even tried an Adaptec AHA-1542CF SCSI adapter that also implements a floppy disk drive controller. That doesn't work either. However, other generic ISA floppy disk drive controller cards work for some reason. I will have to investigate this issue.

Assembly and Pictures

I chose an unbranded AT tower case from the mid-90s decade. It was very dirty, and the plastic acquired a yellowish tint. I might try to retrobright it at some point in time. I quickly converted the case to accept an ATX power supply. In fact, the conversion had nothing to do with the case itself. I have just removed a small retainer metal C-clip from the power button internals. Now, the button acts like a momentary action switch, and it is able to pulse the ATX power-on circuit on the system backplane.

The power button assembly includes an LED, originally green. I replaced it with a three-leaded bi-color LED, as required by the system backplane. When idling, the yellow (GaAsP/GaP, 588 nm) LED chip slowly fades in and out. While the system is powered on, the green (GaP, 568 nm) LED chip is lit. I rewired the LED and terminated the cables with a 3-pin connector that fits the appropriate pin header on the backplane.

These are the two floppy disk drives that I am using with this computer. The front faces are gray. Thus, they don't match the color scheme of the case. But I don't really care about that, given how scarce these floppy disk drives are. Both units are part of the real floppy disk drive series, with a decent build quality and high reliability.

The 1.44 Mb 3½" floppy disk drive is model MP-F17W-02 SMM, made by Sony in 1993. This is the underside. I particularly like the disk motor construction and the heavy duty magnetic shield on top of the motor coils. This unit has an amber front LED.

The 2.88 Mb 3½" floppy disk drive is model MP-F40W-15 SMM, made by Sony in 1993. Again, same construction style on the underside. This unit has a green front LED.

Two CF cards are installed in a dual CF to IDE adapter in a master-slave configuration. This adapter is available in 2½" form factor. I am using a 2½" to 3½" metal adapter that is further installed in a 5¼" adapter.

Here are the two 40 Mb IDE storage devices. These are Seagate ST-351A/X stepper motor hard disk drives. These hard disk drives are not connected to the machine on a daily basis. I am using them only for nostalgia purposes and experimental software that needs to access magnetic drives only. I would've liked the front covers to be computer-grade beige. But they do look retro nonetheless.

This is how the computer looks like.

Although a 7-segment speed display is present, unfortunately, this case does not have a turbo button. It would've been pretty useful for older MS-DOS games that require slower CPU speeds. In addition, the speed display would've switched numbers on the fly. I am thinking about adding a turbo button on the back of the case. It doesn't matter that it is going to be difficult to toggle as I won't be using this function that frequently.

The discolored beige case contrasts well with the black front covers of the storage devices, creating an industrial-looking PC. I initially wanted to search for a floppy disk drive that matched the color of the case. But I gave up quickly since it's hard to find new-old-stock MP-F17W-02 (or related) drives in beige color. However, I might investigate at some point whether a beige front face from a newer MPF 920 drive will fit the old ones.

In the end, I configured the jumpers on the speed indicator to show 40 MHz.

This gray tone on the floppy disk drives reminds me of early Hewlett-Packard Vectra desktop PCs.

And before you ask, no, I don't actually use the EIZO screen in that position. It is quasi-defective and it's pending restoration.

Machine #02: Pentium MMX / 233 MHz

Playing DOOM, Quake, Duke Nukem 3D, Terminal Velocity, and the like, requires a faster CPU. In addition, I wanted to remember the Windows 98 experience. Since an 80386 CPU is out of discussion and the effort of building a 486 CPU-based SBMC is not worth it, I chose an industrial Pentium SBC on a 16-bit ISA card.

Components

This machine is made with the following components.

Known Issues

This machine also has some issues that I haven't found a resolution for.

  • Floppy disk drives do not work -- no idea what is causing this behavior

Assembly and Pictures

The case is an InWin IW-Q500 full tower case that I found dirt cheap at the local flea market. Of course, I had to clean it thoroughly, an operation which took quite some time. But this case is spacious enough for an experimental DIY computer that will have multiple storage devices and a lot of individual ISA cards.

As before, I replaced the single-color green power indicator LED with the same type of bi-color LED (yellow, 588 nm and green, 568 nm). I rewired the LED and installed the required 3-pin connector to the backplane.

The 1.44 Mb 3½" floppy disk drive is model MP-F17W-02, made by Sony in 1993. Again, this one of the real floppy disk drives with a decent build quality and high reliability. Similar to the other floppy disk drives that I am using with the 80386-based computer, the front face is gray. As a particularity, this drive is made in Japan. The other two FDDs are made in Malaysia. There are no visible quality differences between them.

This is the underside. The same construction style as shown above. This unit has an amber front LED.

This CD-ROM is a four-speed SCSI drive made by Toshiba in 1996. The exact model is XM-5401B. It has a gray front face that matches the floppy disk drive.

Human Interface Devices

Since I don't have that much space on my desk, I decided to use only one CRT monitor, one keyboard, and a single mouse to control both machines. Thus, I sourced a very cheap KVM switch from eBay. After some quick maintenance involving replacing old electrolytic capacitors, I had a working unit. Unfortunately, the switch came without connection cables. These proved to be more expensive than the switch itself.

These are the HID peripherals that I am using with my retro computers.

  • AOC 17" Flat Screen CRT Color Monitor
  • BTC 53 Series AT Keyboard
  • Microsoft Optical Mouse, connected to the KVM Switch via USB-PS/2 adapter

I also have a very nice 17" EIZO CRT monitor (pictured above). It developed a defect around the year 2019. The display has a reddish tint that appears a couple of minutes after power is applied. I hope I will be able to fix this issue at some point. Until then, I won't use it.

And in order to enhance my early '90s computer experience, I also have a Hewlett-Packard monochrome VGA monitor that I use from time to time. I'm thinking about sourcing a switchable VGA splitter so that I can connect three monitors and select which one to use. However, this requires a lot of space (that I don't have) on my desk. I'll think about it the next time I restructure the room.

Conclusions and Reflections

It took me a long time (in fact, in the order of years) to build these projects. Even though I designed the schematics and PCBs for all the projects in less than one year, I acquired the required knowledge during many years of hard-working, learning, experimenting, reverse engineering and analysis. I also started raising funds for these projects a long time ago as I knew it was not going to be cheap. However, if I were to build these machines with existing retro hardware components, including shipping costs and possibly import duties, the price tag would probably be almost on par with the DIY hardware. But then there wouldn't have been the fun part.

(2024-edit) It's been three years since I built these computers. Since then, I have done a lot of programming and played loads of games.

Copyright © 2004- Alexandru Groza
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