First power up of the Plexus P/20 dual processor UNIX system

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In our second installment of the Plexus P/20 series, it's time to try to power-up this old machine and see if we can get it to show some signs of life. Machines like this can be complex, so without any documentation or information about it, I'll have to do a lot of figuring things out as I go.

Part 2: This part!

-- Links

Discord channel: (where we are discussing this machine and other stuff)

My Github Repo (with ROM dumps, technical information and images)

Plexus P/20 Brochure:

Plexus Unix:

MFM emulator:

Fujitsu Hard Drive Brochure:

Omti 5200 Manual:

Adrian's Digital Basement Merch store:

Adrian's Digital Basement ][ (Second Channel)

Support the channel on Patreon:

My GitHub repository:

-- Tools

Deoxit D5:

O-Ring Pick Set: (I use these to lift chips off boards)

Elenco Electronics LP-560 Logic Probe:

Hakko FR301 Desoldering Iron:

Rigol DS1054Z Four Channel Oscilloscope:

Head Worn Magnifying Goggles / Dual Lens Flip-In Head Magnifier:

TL866II Plus Chip Tester and EPROM programmer: (The MiniPro)

TS100 Soldering Iron:

EEVBlog 121GW Multimeter:

DSLogic Basic Logic Analyzer:

Magnetic Screw Holder:

Universal ZIP sockets: (clones, used on my ZIF-64 test machine)

RetroTink 2X Upconverter: (to hook up something like a C64 to HDMI)

Plato (Clone) Side Cutters: (order five)

Heat Sinks:

Little squeezy bottles: (available elsewhere too)

--- Instructional videos

My video on damage-free chip removal:

--- Music

Intro music and other tracks by:
Nathan Divino
@itsnathandivino

Adrian's Digital Basement

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HI Adrian, I have a Plexus 25 engineering manual that includes schematics and all sorts of technical information on that system. The P25 (from 1982) is a low end previous model of your P20 (1985) so, there is a high chance that the underlying hardware architecture would be similar enough to propel you towards the right path into a fully working hardware system. I also have both your P20 and the P25 sale brochures which seem to back up my claims. I also have a user manual for the P40. Let me know if you need them, and I can email you the corresponding digitalized documents to some address you provide me with.

pepepistola

Hi, my friend and I had a ton of Plexus machines; P/35's, P/40, P/60's, P/75, P/90 and and P/95's. I also had the complete Plexus tape library of over 5000 mag and cartridge tapes. I had a DEC TU/45 tape deck on my P/75 with the Pertec interface. Also had a Kennedy mag tape drive and eventually, we ended up with 2 Telex (can't remember the model) drives that were 800/1600/6250. We also had tons of manuals. I gave the P/75 to the Diablo Valley College back in the late 80's and the P/90 went to the Computer History Museum. We traded and sold a bunch of P/60's to an outfit in Colorado for cash and the 2 P/95's. My buddy Al, played around upgrading the P/60 from 12.5Mhz to 24.5. Couldn't get to 25. I had the source tapes for Unix SVR5.2, 5.3 and ended up porting 5.3 to my P/95. All I got left is a box of Plexus key fobs, LOL. Fun times, but I started on Linux in 1990 and been with the ever since.

tpkirkp

For a long time I've thought that if a person is truly an expert in something, like, really knowledgeable and accomplished, and also enthusiastic, then it doesn't matter what that thing is: listening to them talk about it is a joy. You're proof of this, Adrian, because I don't know the first thing about any of this stuff you're doing, but it's great fun to watch you do it.

angryscholar

Being a massive UNIX geek and an m68K fan, plus a UNIX system I've never heard of, this series is ticking a huge number of boxes for me. Thanks Adrian

digitalarchaeologist

This is bringing so many things up that I hadn't thought about in nearly 40 years...

johnmccartney

It is a cliff hanger I didn't even know I cared about this server until I got hooked into watching it. Please hurry and do part 3.

moogfooger

As much as I enjoy the higher-volume micros, there's something I find fascinating about these seemingly very well-built professional machines.

xTJ

Really loving this series. I have been in the oil and gas industry all my life. In my 20’s I was a unix admin for Sun and SGI for a US energy contractor. I had such fun playing with the hardware, reinstalling OS adding memory. It brought back so many great memories. Thank you. It’s unfortunate how they were ditched for PC architecture almost over night. However, for at least a few years we all had an old Sun or SGI box sitting under our desks switched off just in case we had to revert. All the best Alex.

MrAsBBB

I've been screaming at the screen for the last half hour "JUST PLUG IN THE HARD We might not be alive in another week.

angrydove

Wonderful diagnosis of a 'headless' UNIX (R) machine trying to work out if it is alive.

bouffman

oh no! a cliffhanger! can't wait to see it boot Unix

_hackwell

I like when you creating such long videos, this is better that all the discovery channels, and watch it even when sleeping

danieltaon

Not only does this system sound like an old diesel, the key switch needs to be in the "Start" position to warm up the glow plugs for a few seconds before going to "Run". 🙂

Jody_VESAR

Adrian's Saturday videos are the highlight of my tech YouTube week. Thanks Adrian!

the_beefy

Thanks for making these great videos. I have a PiDP-11 which comes with a number of vintage UNIX systems. One is System Vr1. I wanted to see a preview of what you might see once you get the real thing working. One thing I found is that the file system is quite fragile if you don't power it down correctly. Had to run the fsck program a lot. Have been compiling the Dhrystone benchmark to check performance.

ablebaker