Booting UNIX on the Plexus P/20 didn't go to plan

It's time to boot the Plexus P/20 into UNIX, or at least try to! In the previous parts I managed to dump the hard drive (for archival purposes) and dump the ROMs. In Part 2 I worked on making sure the power supplies were stable and working well enough to run the machine. Now it's time to actually try to boot this machine into UNIX and see if it works!
Part 1: • What is this rare mult...
Part 2: • First power up of the ...
Part 3: This part
Part 4: • We made some unbelieva...
-- Links
Plexus P/20 Discord channel at Usagi Electric:
/ discord (Plexus channel)
General Adrian's Digital Basement channel:
/ discord
My Github Repo (with ROM dumps and images)
github.com/mis...
Plexus P/20 Brochure:
www.bitsavers.o...
Plexus Unix:
www.bitsavers.o...
MFM emulator:
www.pdp8online...
Fujitsu Hard Drive Brochure:
archive.org/de...
Omti 5200 Manual:
oldcomputers.d...
Adrian's Digital Basement Merch store:
my-store-c82bd...
Adrian's Digital Basement ][ (Second Channel)
/ @adriansdigitalbasement2
Support the channel on Patreon:
/ adriansdigitalbasement
My GitHub repository:
github.com/mis...
-- Tools
Deoxit D5:
amzn.to/2VvOKy1
store.caig.com/...
O-Ring Pick Set: (I use these to lift chips off boards)
amzn.to/3a9x54J
Elenco Electronics LP-560 Logic Probe:
amzn.to/2VrT5lW
Hakko FR301 Desoldering Iron:
amzn.to/2ye6xC0
Rigol DS1054Z Four Channel Oscilloscope:
www.rigolna.co...
Head Worn Magnifying Goggles / Dual Lens Flip-In Head Magnifier:
amzn.to/3adRbuy
TL866II Plus Chip Tester and EPROM programmer: (The MiniPro)
amzn.to/2wG4tlP
www.aliexpress...
TS100 Soldering Iron:
amzn.to/2K36dJ5
www.ebay.com/i...
EEVBlog 121GW Multimeter:
www.eevblog.co...
DSLogic Basic Logic Analyzer:
amzn.to/2RDSDQw
www.ebay.com/i...
Magnetic Screw Holder:
amzn.to/3b8LOhG
www.harborfrei...
Universal ZIP sockets: (clones, used on my ZIF-64 test machine)
www.ebay.com/i...
RetroTink 2X Upconverter: (to hook up something like a C64 to HDMI)
www.retrotink.com/
Plato (Clone) Side Cutters: (order five)
www.ebay.com/i...
Heat Sinks:
www.aliexpress...
Little squeezy bottles: (available elsewhere too)
amzn.to/3b8LOOI
--- Instructional videos
My video on damage-free chip removal:
• How to remove chips wi...
--- Music
Intro music and other tracks by:
Nathan Divino
@itsnathandivino

[@UsagiElectric]

Heck yeah, let's go! I'm in love with this machine, and can't wait for future episodes!

[@samuelcolvin4994]

They really don't build them like that any more, I miss the old IBM and Zenith build quality, the days when your PC doubled as a bludgeoning weapon and anvil🤣

[@JCCyC]

When I first saw this series my first thought was "damn, this is Adrian's Centurion!"

[@bouffman88]

@@samuelcolvin4994 Do you miss having to lift the damn things? Sun workstations were pretty heavy too

[@MacRabbitPro]

Holy cow! About 30 years ago I wrote a converter software on windows for a company here in Germany to convert their documents written on their Unix host system with Q-One (!) into RTF so they could open the documents in Word on Windows. The file format of Q-One was very well documented, one large binder. So I have (well, I had) pretty good knowledge of the Q-One document file format. I never thought to hear or see of Q-One ever again in my life.

[@WDCallahan]

Q-office is the office management software from Quadratron! And Q-one was its word processor. I don't remember whatever happened to Quadratron Systems inc... Big in the 80s.

[@theParticleGod]

Do you know of anywhere with more information about these things? I can't find anything other than mentions in magazine articles and software that is compatible with the format from Q-one.

[@idahofur]

@@theParticleGod Very nice. I found a few articles from back in the day. When I got into computers one of the reason the white box computers took over was software piracy. Not that is didn't happen on other systems. A good example was Wordperfect for dos was all over the place. Oh and one article says one reason for down fall was missing the drive to Windows desktop driven products.

[@WDCallahan]

@@theParticleGod Unfortunately, no. Everything I knew went into that comment. I never even used it.

[@paul_boddie]

@@WDCallahan The Unix World issue (April 1985) that features the Plexus P/35 - the Z8000-based predecessor to the machine featured here - actually has an announcement for Quadratron's Q-Chart and Q-Graph. Reading some of these publications really helps to get some kind of feel for the technologies being used at that time.

[@stevethepocket]

Quadratron is the most 1980s business software name I've ever heard.

[@diamondsmasher]

Adrian, you NEED to get this working again just so we can see why woody would spend such an inordinate amount of time playing “robots” 😊

[@docnele]

Woody was probably the boss to those other users ;P

[@yesterdaysrose5446]

My guess is that I think "robots" is basically the same game as bsdgames "robots". Yeah I can see why people got obsessed with it.

[@dmacpher]

@@yesterdaysrose5446chase!

[@Felice_Enellen]

@@docnele That or he was the night security guard. ;)

[@KillroyWasHere86]

I bet Woody was the office legend.

[@Alcarods]

LOVE that Usagi is helping out! I follow you both regularly, i had a feeling this Plexus would be right up his alley in obscurity!

[@afberglund2764]

Perhaps a bit too modern but Usagi knows all there is to know about bauds and bits.

[@scottlarson1548]

David bought that old Centurion mainframe from the 1970s which no one had heard of and within weeks he found people who had actually worked on the thing.

[@Eremon1]

I used to be a network tech in the 90's up into the early 2000's. Many would be surprised at just how many really old computer systems/networks that are not only still up and running, but are the very core of a lot of the infrastructure around us. Many of the warehouses I've worked in over the years have really old inventory software suites that were so old they needed to source older machines just to be able to continue to run their outdated software. Some of the older stuff is far more robust than stuff built today.

[@wishusknight3009]

Most firms i have come across like that have virtualized much of it. Such as banks and trust companies.

[@timballam3675]

Have to agree, there are a lot of "old" machines running on old PC based systems with ISA interface cards that can't be virtulised. When a machine is hundreds of thousands if not millions to replace sourcing replacement computer parts is getting to be a bit of an art!

[@wishusknight3009]

@@timballam3675 I help out a fab here that still uses a 286 to drive their CnC. The interface card is fussy enough that it seems to only work in specific types of Epson industrial systems. I don't know what makes them so special but there you go. When their original system died, I tried for some time to get something to work, I had an Equity II in my collection that _sort of_ worked. But it was not quite stable enough. The machine had some accuracy issues on it. Luckily I did find another machine of the same type. However it cost many thousands of dollars as the seller knew what he had. It was crazy.

[@KameraShy]

"Outdated software" is in the eyes of the beholder - usually consultants trying to sell new software. Functions like inventory management are well established so the underlying software would generally not need to change.

[@Eremon1]

@@KameraShy In my experience, more often that not, companies continue to use older software because of the sheer expense of changing over. New commercial software itself isn't cheap. Then the cost of the equipment/installation and finally all the time for training to learn new system. It's quite an ordeal.

[@Paul13013]

Old Unix systems used to use a 1/60th of a second pulses from the power supply to switch tasks. If there is an issue with the reset circuit, there might also be an issue with this pulse train. So you might need to troubleshoot the power supply to make sure it's working correctly.

[@sundhaug92]

Yeah I'd check for a 60hz as well as checking the clock-signal from the crystal

[@CharlesBundy-z9n]

Not certain how old we are talking, but for a 68K era machine it would most likely be via programmable timer (for async firing of process scheduler) or derived from the cpu clock for sync firing of process scheduler. I’m not certain what would be coming from or to the PSU.

[@chrisdickens4862]

Fascinating

[@jeffbraxton2893]

Agree. A triggered measurement approach may be necessary versus a "rolling" display on the test gear, as there could be something non-nominal occurring in what appears to be "steady" to the human eye in real time. People tend to rush past characterizing power behavior with a logging/recording monitor when a power supply is suspect, which does take some time-perhaps hours of just the power supply "cooking away" - just ask any C=64 "classic" user that sacrificed one or more ICs due to chaotic legacy power supply behavior! (The overheat condition on the power supply might have been noticed without the motherboards, et al. attached using such an approach.) I am willing to bet that being sufficiently zoomed in on the 5v and 12v plots might reveal "dirty" power spikes even though they look "good" zoomed out.

[@freedomlinux]

Not that it matters much, at 16:12 setting /dev/tty4 to 1200 baud suggests it was connected to a modem. In the late 80s, modem speeds of 1200 and 2400 were common, and 9600 would have been fairly new.

[@gumbykevbo]

Entered comments to say this. In 1986 we had mostly moved beyond acoustic couplers, but it was still all bell-standard FSK. In the early 80's I recall seeing a terminal on a DEC system that was still running at 300 baud. in that era, 1200 baud would have been considered conservative/reliable.

[@AmEv7fam]

Remote access via a dedicated telephone line makes sense. A modem, in the classic sense, is little more than a serial line over a phone line.

[@kpanic23]

Probably been used for uucp…

[@ganswijk]

I was thinking it was a printer, because they were slow too back then, but a modem makes more sense.

[@freedomlinux]

@@ganswijk Good point. I was also considering if it would be a printer, but made some guesses: 1.) Was assuming a printer would be faster. Maybe this is wrong 2.) Not sure if a printer needs any configuration in getty, since the data flow is from computer -> printer. The printer shouldn't need getty listening for it to start up a connection

[@victic31]

Hi Adrian, Love your channel and what you do. Whilst this isn't going to help with your current Self Test fail situation, I have a what I hope is another piece of the info jigsaw for you. The references you found in the directories to 20/20. 20/20 was a Unix based Spreadsheet program from a company called Access Technology. I used to use 20/20 back in the day, although I was using it on Data General hardware. I am fairly certain that is what you have installed on the Plexus, as I distinctly remember the executable being "s2020". 20/20 was a major advance back in the day as it brought a true graphical spreadhseet to the Unix environment. It also had it own key-stroke macro language, a forunner to the scripting functionality of the likes of Lotus 123 etc. Anyway, I hope this info helps, and I would love to see you get this machine up running, if only to see if 20/20 will run as well. I will keep my finger crossed for you in the hope that your are successful.

[@kepanoid]

Adrian, a tip regarding the "find" command: for the "classic" version, you need to give it the -print option to show *any* results. The GNU one and some other modern ones have that set on by default, but that hasn't always been the case.

[@Sypaka]

It's 1986. Buys a workstation for $5000 with Unix. Uses it for playing games. Plays chess for fun. Has fun for weeks. Logs in one day and gets greeted with "Welcome back, Dr. Falken"

[@minty_Joe]

OMG, chess is for nerds. 🤓 Let's play Global Thermonuclear War.

[@seshpenguin]

It's wild still that this company existed in the 80s, did enough work to build out a company, bring out a seemingly pretty advanced UNIX workstation, and then promptly got forgotten by history just as quick.

[@paul_boddie]

Things moved pretty quickly in the mid-1980s. Plexus did Z8000-based systems before this one, but that turned out to be a bad bet, architecturally. Since the Motorola 68000 family was a popular choice for Unix vendors, there were lots of companies trying to make a go of it, and the Unix porting houses like UniSoft probably did pretty well out of all of this. Even AT&T used a 68010 in their UNIX PC, with the port to the 68010 seemingly being done by Convergent Technologies. The P/20 isn't a workstation, but there were 68010-based workstations like the Torch Triple X, also using a Unix port from UniSoft. That was around in late 1985 and had a graphical user interface not unlike those we still use today (NeXT apparently licensed some of the technology on the quiet). Torch had to call it a day in the end, as well. Most of the Unix vendors who used the 68000 family switched to a variety of RISC architectures to remain competitive.

[@marciomaiajr]

"Star Wars? No. I'd rather watch the Plexus Saga from Adrian Digital Basement."

[@MrJakeTucker]

More like Star Trek Next Generation. When I saw all the files beginning with Q I thought maybe this Plexus box was the Q Continuum's server.

[@button-puncher]

@@MrJakeTucker Adrian plays with Q file, Mariachi band appears behind him. Eeek!

[@tcpnetworks]

With it running, we have a conduit right-back to 1984. When computing wasn't so straight-forward. Love to see this machine running again.

[@bradallen8909]

Computing was FAR more straight forward in 1984.

[@federalexpression]

su-username logs indicates that the users were able to su (switch user) to root. The logs would capture what they did as root. It's an audit.

[@nurmr]

Also I suspect that "off" might either have been a general "office" user, or possibly a user dedicated to running shutdown before powering off the machine.

[@jeffbraxton2893]

I thought "su" stood for "superuser" and you need(ed) the unique root password to successfully elevate privileges.

[@nurmr]

Confirmed: /etc/passwd has /etc/gone for the homedir of the "off" user, and /etc/gone/.profile runs shutdown

[@mndx89]

Old and forgotten business machines are really fascinating. I hope you will be able to restore it to it’s fully functional state, it’s a nice piece to add to your collection.

[@rzerobzero]

"Do you want to check the file system? - SURE, let's check the file system......ohwhOW." This gave me major WarGames vibes.

[@RichardFraser-y9t]

It's a Unix system, I know this.

[@ChristopherHailey]

The program it runs is called chkdsk and when things go badly it could be a nightmare.

[@Zwiesel66]

It was very exciting and special, when this UNIX system booted up - a very cool moment 😃I have found a manual for the Plexus P/40 and the P/25, unfortunately I cannot post the link here. There is also a documentation for the OS Plexus Sys3 UNIX 3.1

[@paul_boddie]

Yes, Bitsavers have all these manuals, and you can also find them in the Internet Archive's Bitsavers section.

[@KolliRail]

I'm very confident that the cooperation with Usagi Electric will bring you forward on this!

[@dougsisk1]

"MR" is AT&T for "Modification Request"

[@glennhann938]

Adrian back in the day I was in charge of our y2k compliance and some systems and software that could not be converted to a 4 digit year there was a formula that if you put in a date of 20 or above it was considered as 19nn but below from 0 to 19 the system would consider the date as 20nn. Because who thought this systems would still be running in 20 years.

[@stevethepocket]

Weird that the cutoff date would be 2020 not 2070. Obviously no one would need to put in a current date prior to the UNIX epoch.

[@tigheklory]

This is definitely more interesting than working on Mac and Commodores, just because you have done that a lot in the past. I hope you get a Coleco Adam in the near future!

[@Toonrick12]

Or its Japanese cousin, the MSX. More of a second cousin, but still.

[@dglcomputers1498]

Needs an Acorn Archimedes machine, an A7000 would be a good machine to go for as it uses PS/2 ports for keyboards/mice and is quite compact. Batteries are an issue with most Acorn ARM based machines as it's required to store any settings as a HDD was not needed as the OS was in ROM and as such there was only battery backed SRAM for storing settings.

[@tigheklory]

@@Toonrick12 I think he's had a MSX in the past.

[@johnsimon8457]

Right - micro computers were regarded as toys, especially in the late 70’s. No real shell or file system no concept of processes. They’re practically a nice interface around embedded hardware.

[@yourneighborhood]

Awesome fun video!!! Great to see David (Usagi) jumping in on the project!!!!

[@neilbradley]

2:10 - That circuit board is a work of art.

[@jandevisser2385]

I'm having PTSD from working with similar Unix systems in the early 90s. Seeing that fsck output almost did me in. Seen too many of those where it basically said 'nah bruh, no can do,. Yer drive's dead'

[@TomConder]

For the ‘find’ command, early Unix required the “-print” argument. For example: find . -name log.txt -print Also the shell may expand the wildcard. So you may try escaping it, eg find . -name \*.log -print

[@tommythorn]

There are a few commands still in use that have archaic interfaces by modern standard (find and dd comes to mind). It still annoys me that macOS's BSD derived find, unlike GNU find, requires at least one directory.

[@reinoud6377]

You can always use doubled quote around wildcards

[@martinhow121]

I think that find / -name '*.log' -print should do it. You have to protect the * from shell expansion and leave it to find to work on. I cut my Unix teeth on Unix system 7 on a Fortune 23:16 around this time.

[@awd42]

Yeah, * inside double quotes may still be parsed by the shell; single quotes should fully protect it.

[@rommix0]

Even new versions of 'find' it's recommended to use the "-print" argument. Or "-exec echo {} \;" who love to go overboard.

[@senilyDeluxe]

there's six Toshiba TMM2018 2k SRAM chips in between both CPUs. I've had some problems with those in the past (not just Toshiba. Generally the narrow body form factor 2k SRAM chips seem to go bad a lot. But some of them were Toshibas, so they're not immune to that. And usually, when they go, they get warmer than they should. You might wanna check that. If one of those chips gets significantly hotter than the others, like more than 8°, that's a pretty safe bet). The two RAM chips under the ROMs are Matsushitas. These, especially the wide body chips, are pretty reliable (although - again, I've had a bad Toshiba widebody 8k SRAM that was bad, and the fault was so subtle, the RAM test didn't find it. Then again the machine likely used a very simple RAM test) And then again it's also very likely one of those 74xx logic ICs just died. Kinda rare having a machine this old with that many chips on board just work and stay working.

[@tcscomment]

seeing all these ceramic packages is a blessing for my heart, they look so beautiful

[@humidbeing]

Very happy to see you pull in Usagi and his community on this one. This is their specialty for sure.

[@dru6809]

Adrian - you are now the #1 plexus tech in the world 😊

[@greenmoose_]

I only understand maybe 1/3 of what you're doing... and thats generous! but this series had me hooked for reasons I cant explain! the excitement when you got the hard drive working and imaged was infectious! I had a big smile on my face watching that process!

[@kippie80]

Taking the channel to a whole new level. Was looking forward to seeing some work done here and how Q-Office worked.

[@sluxi]

Love seeing two of my favorite super knowledgeable and friendly retro computing KZbinrs doing a collab! Also really interested in everything about this fascinating system.

[@jpnc2319]

It's a very nice machine. Remembers me the NCR multiboard servers, containing a board with multiple 486 processors

[@nakfan]

Adrian's abc: Always Be Cutting traces 😀

[@exidy-yt]

SO funny how primitive this is even for the time! An Amiga 1000 with WordPerfect 5.1 sold around this time would run rings around that office suite! Mind you, it's not multi-user but you could probably have bought 10 Amiga 1000s fully kitted out for the cost of that single multi-user UNIX box, all of which had 512mb and full WYSIWYG graphics and interconnectivity. What an interesting piece of dead-end history!

[@paul_boddie]

Integrated office systems were an important part of the market back in the 1980s, where you'd have people using multi-user systems in a collaborative fashion, and vendors like IBM, DEC, Unisys and Wang were making serious money on them. There was a lot of skepticism about personal computers and the dodgy and often expensive local area networking solutions available for them, together with productivity applications that only facilitated collaboration in a limited way. Looking back through years of WordPerfect and then Microsoft Office marketplace domination, those skeptics had a point. I don't think that a bunch of Amigas would have sold into the kind of institutions laying down that kind of cash, not least because the Amiga probably didn't have the level of connectivity required, nor the depth of available solutions, either: the buyers weren't exactly looking to run Deluxe Paint. By the time Commodore aimed upmarket at the Unix audience, they showed up with too little, too late, but that is another story.

[@Jody_VE5SAR]

I am now fully invested. 🙂love the "hand-talking" above the MB - classic! Keep up the great work!

[@Birdman_in_CLE]

Very "This old Tony" style of presentation. 😊

[@williamkibira5789]

This has made my Saturday evening. I really do hope you get that motherboard to get past all failing tests. Looking forward to seeing the next video.

[@lemagreengreen]

Very cool to see old System V Unix in action

[@ultrametric9317]

Ha! My first thought was - flash the sign in the sky, summon Usagi-san! :) This is fun!

[@gabrielleeliseo6062]

Usagi-chan? Sailor Moon? xD

[@Herby-1620]

I have a machine from this era (Altos ACS68000) which runs Unix System 3. Its original C compiler was pre-ANSI. Yours might be as well, be sure to check! I was able to get a user based compiler to operate on the system, and interact with the native libraries. Thankfully, I have schematics and some source code of the system. One of the things I was able to get running was GNU tar. Unfortunately, it has been a while (20 years?) since I turned on the machine, so I'm a bit rusty. Good luck in your travels.

[@IcyTorment]

It would definitely have to be a pre-ANSI C compiler, given the time frame.

[@fubaralakbar6800]

The bodge wiring job on that machine is just totally professional.

[@zrodger2296]

"I think it's doing something!" 😅 Love the enthusiasm!

[@MultiPetercool]

If you want to transfer over the serial ports, configure UUCP. It’s all we had in those days.

[@erinwiebe7026]

I'm looking forward to future videos where Adrian spends weeks (or longer?) playing robots & eventually topples woody's score!

[@kanalnamn]

You can transfer files by enabling logging in your terminal, and use uuencode on the machine with the console as output. (UUCP were on there, so uuencode should too.)

[@petergathercole4565]

The terminal program from uucp should be cu. But it is probably easier to just cat to a file. For binaries uuencode/uuencode in probably the best thing to use.

[@05Forenza]

This particular series I'm very invested in. Can't wait for part 4!

[@Codec44144]

This is a great combo of hardware archeology and software archeology. ❤❤

[@RetroBytesUK]

Absolutely loving this serise of videos. Adrian fixing stuff & and old obsure unix machines, everything here is right up my alley.

[@tomahzo]

I'd love to see a historic retrospective on Plexus. It'd be wonderful to have former employees talk about the company and what they did and their stories :).

[@xxHANNONxx]

Over century of motion picture, and the cliffhanger concept has peaked at the Plexus saga!

[@CubicleNate]

What a cool machine! I do hope that you are able to build a Qemu spec so that this machine can live on. You are doing GREAT work sir!

[@quadmods]

SCSI ID 7 is usually the controller. So ID0 is the drive likely 6:44

[@ganswijk]

Yes, it makes sense to number the harddisks from 0 onwards and put the special things at the end, so from 7 backwards.

[@MaddTheSane]

I think ID0 might be the whole Shugart module, so the floppy and the HD.

[@nilswegner2881]

​@@MaddTheSaneThat makes the most sense, yes. The interposer likely sets these two up in their own LUNs.

[@wishusknight3009]

I don't know where the tape drive would be then, as I thought adrian said it was a directly connected scsi device.

[@metaforest]

The host end of the SCSI bus doesn't have an ID. ID0 is likely the interposer([LUN0, LUN1]FD/HD) and ID 7 is likely the tape drive. While they are often treated like device IDs the SCSI ID is actually the priority of the device. ID 7 has the highest priority ID 0 the lowest. Though it was seldom implemented, SCSI devices could assert control of the bus and that is what the priority level was for.

[@KAPTKipper]

This desk-side chassis reminds me of the Spacstation 330 I used to own. 1200 baud would have been a Modem port, 1200 was a fast modem in 1986, wasn't long until 9600 was around though

[@retrozmachine1189]

What that much time playing games Woody was clearly the sysop.

[@moogfooger]

Well as promised, here is the next installment. Whoopee! Now I can get my next FIX. Thanks a ton Adrian.

[@10p6]

Interesting video. It is an huge computer for 1985 when a 68020 (1984) based system (something like a re engineered Atari ST or Amiga, or Mac) would have outperformed a multiple processor Plexus and had a lot more capability.

[@MrJavaman5]

When I first saw the thumbnail for this video, I thought Adrian was wearing a grey dinner jacket, lol.

[@lordhostile]

halfpint huh? considering the year that thing would have been in service, Im willing to bet someone was a Little House on the Prairie fan.

[@IainDavies-z2l]

Thanks for letting us know, I can now relax and enjoy the rest of the day. My life has so much improved with this information and I'll be able to have a good night's sleep.

[@SeraphimCherubim]

I really enjoy your troubleshooting. It helps me become a better troubleshooter.

[@spodule6000]

JANET was (is?) Joint Academic Network, an network linking UK universites etc. back in the day. I think it got absorbed into the internet later.

[@memadmax69]

Man, i would’ve killed to have this machine back in the day.

[@jdkap201]

This series gets more interesting with every new vid!

[@jackhydrazine1376]

You can't be series!

[@DW-indeed]

​@@jackhydrazine1376I am series, and don't call me Shirley!

[@luna-hw9li]

btw: old "find" needs the "-print" option.

[@martijnposthuma3121]

not only that, but you also need to prevent glob expansion when you want to feed it a * for matching, so you must use single quotes, not double quotes

[@mojoblues66]

@@martijnposthuma3121 you're of course right in general, but in this particular case the * did match an existing file so the find command would have printed out that one matching file if Adrian had used the -print command.

[@JohnWojt]

The 1200 baud getty was probably associated with a modem... as that would be the modem speed of the mid 80s

[@Thiesi]

_me, using a 300 baud acoustic coupler until maybe 1989/90:_ 😢

[@berntolovhellstrom8891]

@@Thiesi The Kansas City standard (KCS)

[@SonicManEXE]

Completely unrelated, but my fiancée has had that Star Wars shirt forever! My immediate first thought when starting the video was “how did Adrian get her shirt?” 😂

[@TheDefpom]

You are assuming the reset circuit is bad, it is more likely the power supply has an issue which is causing the reset to activate, I think you need to be looking at the power supply. Dirty power or glitches from the supply could easily be causing logic board issues.

[@Jah_Rastafari_ORIG]

Fingers crossed that in the coming weeks, some schmoe (/schmoette) comes across a box of manuals (as used to be common in the 80s) that says "PLEXUS" who writes and says, "Uhh...w-would these help..?"

[@BrainboxccGames]

great video, really interested on what is happening with the P20. Saw you in usagi's discord getting to the bottom of this, keep up the good work!

[@CharlesBundy-z9n]

1200 baud was for a modem :) probably dial in for work from home folks. EDIT: I need to read comments somebody beat me to this! I doubt this is a printer TTY as even the old dot matrix printers circa early 80’s would allow 9600 and higher. Had an Epson that was running 19.2K baud in 1986.

[@Kolor-kode]

Can't say I'm not a little disappointed the games dir didn't contain globalthermonuclearwar

[@Flying0Dismount]

You really need a thermal camera as part of your process. Even if a device "works", it may have faults that will cause it to fail in short order and a thermal camera will tell you quickly whether there is a component that is abnormally hot and that you should shut the system down ASAP and diagnose vs. continuing to tinker...

[@ericksonlk]

Looking forward next episode. This is a very interesting project. Lots of mysteries here!

[@rager1969]

It would be cool if one of those users recognize this as the system they used and shared some background/history.

[@MagikGimp]

This is huge. Both figuratively and physically!

[@johnclements7368]

Adrian are using Unix V7 or Sys3? I have a P\40 manual that may help. A hardware description in the manual appears very similar to the P\20. If you send me an address I can email the file to you. John

[@twocvbloke]

One of the pitfalls of reviving old computers, the unexpected conking out of ICs that do important stuff, only in this case it's harder to figure out which one is at fault without pulling them and testing them one by one, which could be a long process... :S

[@AlsGeekLab]

This is a really good series, glad to hear you are continuing to persevere with it!

[@gertsy2000]

Sharing the love. Good luck getting it back.

[@Mainyehc]

I did not expect this saga to take the turn that it did, but I hope the outcome will actually be awesome!

[@shiroshine7227]

that green and blue towel/mat must have a story.

[@tomr3422]

This is a better origin story for skynet then those terminator movies

[@stormx2827]

Such a beautiful machine - top notch industrial design

[@necro_ware]

Very exciting series! Thank you.

[@nicksmith4507]

What a rollercoaster! Hope this is not the end of the story

[@birrextio6544]

20/20 is a spreadsheet software, it was popular back then. I had the tape but I gave it to a collector. Bus error is an address that goes out of memory, the mac disabled that signal so they never got that error. I would guess you have a bad data bit on the address bus or maybe the mmu. Check all bits on the address bus and see if any of them has about 2 volt instead of a clear high or low state.

[@RetroBytesUK]

The discord invite links have expired, no problems if thats intended, but if not I thought you might like to know.

[@not_crazy]

I would also like an updated discord invite link...

[@myleft9397]

woody was doing a lot of procrastinating at work, level 63 o.O. Great video. How about all those wires, factory bodges? Maybe a lose connection?

[@Breakfast_of_Champions]

Since there seems to be a general lack of bypass caps on this board, I'd suspect something's up with the PSU causing these obscure failures. I know it's a blind spot of Adrian's but the PSU must have been manufactured with some very tight specs to enable operating a battleship like this almost without bypass caps.

[@John-jl3ky]

Great Video Adrian, I know you work very hard.That is disappointing, but its exciting that there is other people working on it. I look forward to more info!

[@brianbrwa]

Maybe this was Burleigh's humor coming out from Hardware Structures. Logisim with a clear cycle positive signal...

[@TimothyMusson]

35:15 - Is that an Ohio Scientific T-shirt Adrian's wearing at the end of the video?! I think it might be! Cool :)

[@doppz]

woody absolutely killing it in Robots

[@wirebrushofenlightenment1545]

So glad you haven't given up on this one. It's a very sweet machine.

[@keithmarlow143]

I'd be checking the stability of the power rails, look for AC on the rails (put your multimeter on AC) - it should be well sub 0.1v. If it isn't it could be a component has gone 'shorty' and its pulling the power supply just too hard to be stable. A good 5 or 6 digit meter in DC should allow you to work out where the bad component is by finding the lowest voltage reading. Also use an IR camera if you have one, you might find a hot spot. The reset flopping around indicates a power supply issue to me, check for tantalum caps.. something I did when repairing an 80's HP 6 digit multimeter was put appropriately matched resistors and LED's on each power rail, so they had the same brightness during normal loading (i.e. slightly higher resistor value than the LED resistor calcs say, so your closer to the voltage conduct knee of the LED, a variable benchtop power supply can help you dial this in, given the different voltage drops of LEDs) - anything bad on the power rails would be visible very quickly. You will also see a brightness pattern as loads come and go.

[@RadioTeal]

Hi Adrian: If memory serves, SCSI ID0 would be the last ID on the chain and ID7 should be the SCSI controller (in this case the interposer board). From memory, most times the Hard Drive and Tape Drive would have their own IDs, so like ID0, ID1, etc.... and then ID7 is the controller itself. Great project and very interesting machine.

[@proteque]

this is one of my favorite serie for ages. looking forward to see whats next.

[@byteforever7829]

I'm commenting near the start and fingers crossed 🤞 great video on a system that sounds like it needs your video documenting for the future

[@GeomancerHT]

I would love to see a collab with Tech Tangents.

[@LeftoverBeefcake]

Or with Veronica Explains since she was a sysadmin in a former life (to help with the software side of things).

[@CyroTheSpider]

Honestly, NCommander has hands on experience with these old Unix machines, has worked with them and is an actual developer.

[@UncleKennybobs]

Why? How would that help?

[@ShawnGillette]

​@@UncleKennybobsbecause it would be cool and fun? Tech Tangents *often* fails and comes out with a plan moving forward and positive attitude; this video is similar, as are lots of ADB vids. Seems like an ideal fit to me.