The Rarest IBM PC Clone in the World!

The Centurion is one of my all time favorite minicomputers, but did you know, they also made an IBM PC Clone? Well, they almost shouldn’t have. The story of this thing is absolutely bonkers, and the story of how it got here is just as bonkers. So, tag along as dig in deep with a history lesson, and then try to get this old PC back up and running!

The BIOS has been uploaded here:

If you want to know more about the Centurion, the wiki is full of just about everything we know:

Also, we now have some epic shirts for sale!

Come join us on Discord!

Intro Music adapted from: Artist:
The Runaway Five Title:

Thanks for watching!

Chapters
0:00 This is not Doug Demuro
0:31 Brief history of Centurion
2:50 Why does the EDS PC even exist?
4:44 How did it get here?
11:11 Cleaning up the monitor
12:42 Does the monitor even work?
15:18 Let’s dig into the PC itself
17:51 A closer look at the motherboard and cards
25:27 Putting it back together and turning the switch
26:49 Let the troubleshooting nightmare begin
31:35 Will it boot?
32:56 I hate foam and foil keyboard with a passion
36:41 All clean and back together, will it get to DOS?
39:29 Plugging the Centurion into the Centurion
42:25 Kitties!

[rkinca]

As a 31-year EDS veteran, this was a great trip down Memory Lane. Actually used one of these for quite a while at EDS. They were actually pretty reliable. Thanks for the deep dive on both the history and the machine itself.

[AsbestosMuffins]

such a funny flex to build an entire PC to just get a better price

[michaeldibrino]

My father was a tv repair man. I remember he used to press a service button inside the set to reduce the picture to a single horizontal line. He would then adjust the color controls to get a pure white color balance.

[johnnywarren]

David, words cannot describe how pleased i am that my uncle chose you to become the caretaker and story teller of Centurion Computer. Your excitement and enthusiasm for both the hardware and the people behind the scenes is truely amazing. Thank you for being the man that you are, and continuing share with the world, the time of Centurion Computer.

Looking forward to meeting you someday. 😮

[RonLauzon]

I worked for EDS back in 1987-1997. At my first position, they had several EDS PCs. I never knew they were more than just a cheap clone.

[kurtsvids]

10 years at EDS. My first job at the company was working for the Tech Products Division in Warren, Michigan. I repaired these as well as IBM PC Machines. There were quite a few of them in the organization. The failure rate on these machines was high and our client, General Motors, hated them. They were happy to replace them with IBM machines. Glad to see that you could get one working. No such thing as a ram tester in those days. You would just populate one bank with 64K of known good chips and add banks until one failed, and then swap chips in the bank one at a time to find the culprit. One PC could take all day to fix, but they did give us overtime!

[byteram]

12:19 Those modules are called thick film hybrid modules. The resistors are the black strips printed onto the ceramic substrate.

[BlackEpyon]

The horizontal line test is reminiscent of the "beam find" function on analog oscilloscopes. That's a freaking amazing monitor! Just for the convenience of not having to open it up to tweak the settings!
Also, just an FYI, those POST cards will verify that you've got voltage on the rails, but you're not likely to generate any usable codes on a PC/XT class machine. Still useful to get one though if you're delving into the vintage PC usagi-hole.

[DarkestVampire]

Usagi upload: This is a good day

Usagi uploads a video about an IBM clone: HOLY SHIT WHAT I NEED TO WATCH THAT

[BlackEpyon]

RAM errors are a PITA to diagnose on these early PCs. One of my XT machines was giving RAM errors, but the RAM chips themselves were perfectly fine. Turned out the issue was a single bad NAND gate that wasn't properly switching the active banks, but I had to reverse-engineer a quarter of the motherboard in order to find where the common link was. Replaced that 74x00, and it's worked perfectly ever since.

[derekloudon]

I find your channel very nostalgic (I am 75) and I love your enthusiasm! Keep going please!

[toddbu-WKL]

This episode is AMAZING! Not only for for the fact of the Centurion clone, and the history for why it was made, but what impresses me the most comes at the very end where David hooks up the PC as a second data terminal to the Centurion mini and logs in. I ABSOLUTELY LOVE the simplicity and capability of a remote terminal using serial data transfer. There is nothing that beats the fact that you can take a dumb display device and hook it to a smart computing device with three wires (and maybe a little FSK action in between) and do a lot of real work. To this day, I still spend most of my day working in a terminal window. The RS-232 connection has been replaced by SSH, but otherwise things are functionally equivalent. I never think twice about whether the computer that I'm connected to is a VM running on the same laptop as my terminal emulator, or is a computer in another room near me, or is in a data center on the other side of the planet. And if Elon Musk has his way, that computer might someday be located in a colony on Mars, though I suspect that latency might become an issue at that point. 🙂

[michaelrogers]

I know this is a silly thing to notice on a video like this but your appreciation for the person who helped you with the floppy and the troubleshooting, the way you showed genuine appreciation for another man feels rare. Like I don't see men be so genuine often towards other men and it was really cool. Also, great video- I know nothing about old computers like this but it's still my favorite type of entertainment.

[shantohuq]

When you disconnect one input of an AND gate (like the SN74LS08), it effectively becomes a buffer. by cutting one leg of the AND gate, you’ve transformed it into a buffer.

[mycosys]

The SASI adapter is on the graphics card to allow you to connect a SCSI/SASI Graphics Digitiser tablet ;)

[oldnepalihippie]

As someone who worked on the IBM 5150 back in the day, it was so awesome to watch this video today, in 2024. I remember all the chips, and how easy it was to tear apart and customize to any hobbyist desire. Makes me think of WoZ as well, and his protestations when things went non-standard. But I am glad I worked in the PC-Compatible era of tech, it was a wild ride... ALBIET at a much much slowwwweeeer pace than today.

[Krivulda]

That sound of the HDD is very healthy, it's what ST-238R is supposed to sound like ;)

[alyssonrowan]

The cut leg on a TTL chip used to be a fairly common feature - either a retrofit option was added or else it was part of a retroFIX for some error on the motherboard - quite often a RAM configuration or system clock add-in. Yes, the maths coprocessor was an 8087

RGB Monitors Inc. Nice monitors for the time! The horizontal line is for vertical centering of both the display AND convergence on the three electron guns.

SCSI/SASI port on the display card - I came across this in a couple of systems - apparently it was for frame capture to an additional device, and for fast frame loading from the same. I *think* I have also seen it used for light pen on a drawing system (that needed the maths co-pro installed).

PC/3278 IBM Terminal emulator - I used to see a lot of these when the real terminals became an additional obstruction on the desk and being able to switch over to the mainframe when required was seen as a boon.

Hard drive controller - that one should be able to handle MFM drives as well as RLL drives (Jumper selection?) All of my WD controllers back then could handle FM, MFM and RLL drives plus (according the the manuals) several proprietary formats.

Bad RAM. One bit is enough to stall POST. How many times have I tried to find the bad chip.

[bobweiss]

The "flat line" mode in the test switch is likely the same as the "service" switch on a color TV. Used for setting up the CRT bias/screen controls to adjust the greyscale. You adjust the RGB screen controls to get a white/grey line, and the CRT bias to make the line barely visible.

[tommythorn]

Didn’t feel long at all. Congrats and thanks for sharing