The PDP-11/23 Plus Works!

Last episode, the PDP-11/23 11/03 Hybrid we were building absolutely crushed me. Well, to be fair, we never even got as far as testing the CPU, we got crushed by the power supply. I threw everything I had at it, and emerged the very opposite of victorious. I retreated to my corner, and armed myself with more knowledge, and now, stepping back into the ring for round 2, I absolutely will emerge victorious! How though? Well, you’ll just have to watch to find out (it was negative voltage).
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Intro Music adapted from:
Artist: The Runaway Five
Title: The Shinra Shuffle
ocremix.org/remix/OCR01847
Thanks for watching!
Chapters
0:00 It’s cold y’all
2:29 Revisiting the regulator design
7:00 The negative voltage
8:56 Working on the -15V rail
11:34 A tale of two diodes
14:13 Come on man, you can do this
16:45 Nice, the PSU works. Now what?
19:46 Legen- wait for it -dary
21:38 Let’s get it to misbehave a bit
24:26 Time for a lot of y’all to click away
26:00 If you clicked away, you missed out on this
27:05 Sunny-kun!

[@CuriousMarc]

Using a 7805 as a buck converter regulator, I didn’t know of that trick! I guess cheap buck converter controllers did not exist quite yet! Quite clever trick actually. I might reuse it…

[@salan3]

I have seen this on old equipment but not for decades. When I worked at Tektronix, I spend most days working on either sampling systems or switch mode PSU's

[@SarahKchannel]

but shouldnt there be a shotkey diode or something at the output of the 7805 to avoid back driving ?

[@MyCrazyGarage]

Years ago i was given an old PSU at work to fix. It had a 7812 in an TO-3 package and 8 (!) TO-3 Transistors to boost it. I think it was something like a 20A 12-14V Output. Was probably from an old Camper Van. I was quite surprised back then. I also never saw something done that easy before. Oh boy did the heatsinks get hot....

[@roman65536]

Take a look old 78xx datasheets from the 80s (can't remember whether ti or sgs). Back then I build it and worked fine.

[@UsagiElectric]

It's a really cool design! All the years later and DEC is still taking me to school, haha.

[@darkwinter7395]

But... but... there's wabbits at the end! And they're wabbing! Waboursly!!! 🐰

[@seanys]

The colours of that portable terminal are exactly the same as my Mum’s curtains in our house during the 70’s.

[@Runco990]

Or the carpet in my parent's patio back then!

[@TechBench]

Guaranteed to never yellow with age 🙂

[@Zeem4]

My jaw dropped when you folded open the keyboard on that portable terminal. It's so gorgeous.

[@Honeybearsphone]

It is a sexy looking little terminal

[@kerryedavis]

My Otrona Attache is a full PC-XT computer in that size.

[@wotsac]

They should have sent a poet

[@Relkond]

I’d heard a story about the PDP-8, where the operator had nabbed the sign from a PDP-10, and placed it onto the PDP-8. When asked about the sign? His response was: “octal”.

[@trevorhanlin4247]

My 7 year old daughter watches these whole videos with me just to get to the end kitties, bunnies, and other animals. She wants to be an engineer, makes my banker heart proud!

[@d614gakadoug9]

There are lots of wild bunnies ( _Lepus townsendii_ white-tailed prairie hares, often called jack rabbits) around where I live. There are also kitties ( _Lynx rufus_ ). The kitties like the bunnies, but not the same way I like the bunnies.

[@xephorce]

i love the cute animals at the end. that's the whole reason i come here. the tech vid is great but the cute bunnies and kitties are the lifeblood of this channel. Thank you again for an amazing video.

[@merseyviking]

14:00 took me a moment to figure out why you were trying to read the current through the screwdriver 🤣

[@reddashgames7550]

Thank god i'm not the only one.🤣

[@TheOriginalDoctorG]

My wife and I always stay all the way to the fuzzy friend clips at the end!! 😊 Was celebrating with you for that first boot-up. Can't wait to see that portable terminal up and running!

[@UsagiElectric]

The fuzzy friends are the best part of the video! Getting the ADDS up and running is going to be a proper journey, and I'm super excited to tackle it.

[@johnm2012]

I came here to say the same. I always stay to see the kit or the bun at the end.

[@glenncaughey5044]

I stay for the bunny too 😎🐰

[@Colaholiker]

Let me join you - I never close the video early, for exactly this reason!

[@tiepup]

The adds terminal is very cool. Glad to see the PDP working again, and thanks for resolving the cliffhanger you left us with last time.

[@UsagiElectric]

I'm super excited about the ADDS! The PDPD defeated me last week, but I was absolutely not going to give up on it, so I had to dive right back in.

[@exidy-yt]

Click away?? NEVER!! I even let the bunny run! Congrats on getting the PDP-11 mini back into the land of the living! There seems to be quite a lot you can do just with the on-ROM diagnostics so that's very impressive on it's own, it's going to be even more awesome when you get storage on that bad boy and can use the huge PDP-11 software library! I can say that I don't think any of us mind you focussing on this unit until it's going fully again, as long as it dosent burn YOU out. Keep it up!

[@GodmanchesterGoblin]

Those orange keys caps! I painted my bedroom that colour in 1973!

[@hangonsnoop]

That portable terminal looks like it escaped from an episode of Doctor Who.

[@figueroalabs]

Great to see a PDP/11 in such a nice condition. And yeah, the Envoy portable terminal made me drooooool.

[@UsagiElectric]

One of the things that I don't like about the later PDP-11s is that they use so much beige. I think the Envoy will really add a splash of color and life to the PDP that'll make it look epic at events!

[@edgeeffect]

​@@UsagiElectricyeah... that keyboard is FABULOUS!

[@michaelardai9703]

Reminds me of the ADDS Consul 580 we had back at school. Same keyboard colors.

[@TomFynn]

A true "IT LIVES!!!" moment. There should be lightning and thunder in the background.

[@jean-jacquescharlet5296]

It's alive, it's alive. Frankenstein right ? Greetings from FRANCE.

[@michaelpelley2815]

I have to say: Nothing screams 1970's than yellow, orange and brown 🙂

[@merashallan]

The first computer I ever used was a PDP 11/23 with 2-bit MMU. It ran UNIX v7 (a pre SysV version) and had two terminals attached - an ADM3a and an ADM31. The disk storage was two RL02 removable platter drives. This system sat next to an old Data General Nova 800 in the university lab where I was a high school intern of sorts. I'm so glad you got the power supply working. That's an interesting switching design I had never seen before.

[@Dark_eVader]

I can' t imagine that there are at least 50% that click away and miss the furry goodness at the end of each episode. Man I loved this episode and totally want that portable terminal with all those orange keyboard goodness for myself. Too bad stuff like those are hard to come by here in the Philippines.

[@sn1000k]

We all get to 'have' it because he shares it so generously with the community

[@Dark_eVader]

have what? @@sn1000k

[@sn1000k]

Dude that portable terminal is IT!!!!! It wins the computer aesthetics contest, hands down, its over!!

[@nutsnproud6932]

When I learned electronics the Rule #1 was "Thou must check ALL voltages".

[@denniseldridge2936]

You are one tech I would never bet against as I've never known you to fail to get anything you work on running. For us geeks it's a bit like a Hollywood action movie in which you know the bad guys will be defeated by the hero, but you still have the thrill of the action itself. I will give credit to you working as a team with the great viewers who give their knowledge and time to help you. In fact, that is one of the great things about this channel, the community spirit that gets things done. I can't wait to see some software fire up on this "cute" little PDP lol. And of course to see the whole portable build come to fruition. Also, that portable terminal is really cool - I can't wait to see that come to life. Cheers!

[@IainShepherd1]

Woooo hype! That ADDS Envoy is so funny somehow. Peak 70s. I guess it will slot into your car space easier!

[@BBHexKey]

All those people clicking away at the outro also miss out on bunnies.

[@stephenchoiniere2530]

I saw the processor and I recognized that was a DEC part number, the other number (6007-38)is the lot number of the chip run in DEC’s semiconductor facility in Hudson, MA. I worked in that facility from January 1979 through May 1998 for DEC and then from May 1998 through April 2015 with Intel. I saw the date code 1983, I was an equipment technician working on the process equipment on the fab floor at that time. Best company I ever worked for, nothing has matched it in my career.

[@logipilot]

I'm always viewing til the bunny. My bunny Otto past away last year. He was 14(!) years old. Wishing your old bunny all the best!❤

[@belstar1128]

did he taste good ?

[@AerikForager]

I like to stick around for the fur babies at the end anyway, so win win! ;)

[@timc3600]

Some very dated memories here that might help (or might be a little wrong.. Hard to tell now). 8 inch floppies are RX01/RX02, the 5Mb single platter "Dustbin Lid" drives are called DL01 and DL02 as in Dustbin Lid 1 and Dustbin Lid 2 If you need to build a system, there is SYSGEN. Formatting floppies, with badblock detection is init /badblocks RX01 or whatever other device you want to use. I recall a diagnostic disc that could be used for hardware testing. Not sure if anyone has a copy of that on-line now ? I'm sure there is other info on-line. I noted a pdp-11 site in the Netherlands that had handy info, but I'm sure there are many others too. This system was also my first introduction to lots of new things including Advent, the adventure game, assembly language, multi-user systems and a bunch of other skills that have proven handy through my career. Thanks for the non-volatile memories.

[@andysmith8649]

I try to watch til the end. The bunnies are so cute.

[@Jim-be8sj]

I always stay until the end and often rewatch if I see a bunny. :)

[@smrp1984]

27:06 well of course I hang out... this is the part I hang out for BUNNY!!!

[@keresztesbotond740]

Well, moral of the story is to check ALL power rails before debugging a specific one. Although you'd be forgiven for not noticing that the 5V section used the -15V reference. It's quite a sneaky trick and hidden well. Didn't catch it at first either.

[@annihilatorg]

Who can leave an Usagi video early? That's how to see the bunnies and kittens!

[@mikeziniti]

I LOL’d when you snapped the diode in half with the screwdriver. Please forgive me.

[@EmperorKonstantine01]

Excellent, I get excited and celebrate same time you do when something works %100. I always watch till the end so I can see the Wabbit!

[@TheHylianBatman]

I couldn't imagine not watching your videos all the way through! Sure, sometimes I might put it in "podcast mode", where I'm not watching and only half-listening, but I couldn't imagine stopping the video before it's over! That's an ultra-cool portable terminal! I love the color scheme! It's so garish, straight out of the 70's! Fantastic work with the power supply! Glad to see this project wrapped away for the time being, it's nice to see you accomplish things! I can't wait to see what this computer does next time!

[@muadeeb]

I'm here for the bunnies. Not just the retro computing.

[@dickot]

Used to run a DEC repair center back in the early 80s, fixed a lot of those following the same process. Good work!

[@Zadster]

For the second week in a row, it is the same component failure as Adrian's Digital Basement experienced (1N4148 diode failed short). Adrian also had a circuit schematic that didn't show all the components! Although I suspect in this case, there was an avalanche failure that took out several components. Another brilliant learning exercise. I wonder if the PSU design has evolved from a previous one, because the architecture is rather odd. It just has that feeling of being adapted from something else.

[@juanmiguelcortarello6823]

First, the "mobile" ADDS terminal is so sweet! Very cool. And who would want to skip the bunnys and kittens. Very nice outros! Saludos desde Argentina!

[@nakfan]

Such a joy to watch your adventures - right through to the end with the super cool bunny 🐇 Thanks for sharing your enthusiasm with us. It’s sooo contagious 👍

[@VincentGroenewold]

Glad I'm not part of the 60%! What a gorgious keyboard that is! :) Great to see the troubleshooting, rabbit holes are frustrating, but very good to learn from.

[@paulalmquist5683]

I enjoy your enthusiasm. I am also learning how much I do not know about trouble shooting and circuit analysis. Well edited video too. That is a nontrivial task too. The school I worked at decades ago had a PDP11/44. It suddenly went down one day. Why was a mystery for a while. Turns out that a custodian was cleaning the floor. On the back stroke of his mop the handle hit the power switch. A guard was put over the switch panel. I do not know what happened to it when it was retired. It was a fun machine to use. Thanks for the educational and entertaining videos.

[@TastyBusiness]

Nicely done, DC works! Early switchmode minicomputer PSUs can be a bear. The Envoy is looking awesome, and bunny is the icing on the cake.

[@makerofthingsunique]

I always wait to see the rabbit 🐰

[@rogeratygc7895]

My (unreliable?) memory tells me that I learnt in 1971 that ODT stood for Octal Debugging Technique. I was using a DEC Linc-8. What a neat regulator circuit!

[@DanBowkley]

You need a Harbor Freight item 63697 mini pick set. They're awesome for getting under mostly desoldered stuff and giving them just enough persuasion to let go of the pads. I think the whole set is like a buck or two.

[@musiqtee]

26:04 THOSE were the colors of my entire childhood…! 😅 (turning 58 next Friday…🙈👍)

[@TRBORADIO]

I'm so glad you could bring it to life again! And I'm glad that I still have some sharp eye left to detect electronic failures :). Now you have a new slogan for t-shirts -15V DC :)

[@ckworton]

Holy H! The colors of that ADDS Envoy. 😂

[@donmoore7785]

Nice work! CPU and memory and terminal interface working. Just a tip - the fact the input to the 7815 was less than a volt was a tip that the 7815 was a clue that the issue was upstream (transformer or diodes).

[@alabamacajun7791]

Nothing would warm up a frigid Texas computer room faster than an awesome 6AU6 Vacuum Tube computer. Just amazing stuff we had back then and all we wanted was MORE POWA. Using a 7805 as a voltage reference/startup buck supply, interesting.

[@b4cktr4k24]

I loved when you said the CRT terminal wasn't exactly portable and then pulled out the bigger, heavier "portable" ADDS! Gotta love those huggable luggables!

[@macgvrs]

I know a Kaypro lug-able isn't a terminal but that was the first thing I thought of when you opened the portable terminal. Very neat. I think I was celebrating right along with you when the power supply came up working. Great job of figuring that out.

[@esra_erimez]

Those vibrant ABS keycaps on the portable terminal are gorgeous!!! I just got my dad a Televideo 920c for Christmas.

[@retrozmachine1189]

Using a 78xx as the basis of a switcher rang a long silent bell. It's one of the configurations given in some manufacturer's datasheets.

[@andrewlarkin200]

When removing through hole components that you know you are going to replace, cut the legs first and then all you need to do is desolder the remaining part of individual pins. This saves stress on the pcb and is easier and quicker. You can still check part function from the remaining stub of legs on the part for post mortem purposes. I like using ceramic tip locking (reverse) tweezers for holding pins while desoldering them.

[@MVVblog]

I always stay until the end, and boy!!! That terminal made me hXXXy as a pig!

[@justcasris6991]

oh my god, i literally screamed out loud when you pulled out that portable terminal, that thing is fricking beautiful and i'm so excited to see you work on it~!

[@joefarr3304]

I first saw that ADDS terminal on an episode of Hawaii Five-O in the 1970's and I soooooo wanted one. Great episode and well done getting the PDP running again.

[@SignalDitch]

That Envoy is a thing of beauty

[@chriholt]

Amazing - I never thought I would ever see a "portable" PDP-11 - I always assumed that they would take up at least one rack!

[@osrr6422]

I know enough about basic electronics to understand some things. That power supply setup is absolutely genius, and interesting at the same time. It's cool to see vintage designs.

[@ShellacScrubber]

Wow ! that ADDS Envoy is a thing of beauty ! ...those orange and yellow keys !

[@skfalpink123]

That 'ADDS Envoy' terminal just screams out "Welcome to 1973!"

[@dmatking2000]

I always thought those orange vintage theme keycap sets were just artistic license. So awesome to see that orange and yellow!

[@drozcompany4132]

Now THAT is a mini I wouldn't mind having in my collection! Awesome that you got it working!

[@zehalmeida]

He says the Adds terminal is easy to transport after breaking his personal record while dead-lifting the machine from the ground. Jokes aside, I love how you keep rotating projects between videos to keep them "fresh", really speaks how much you prepare yourself to take care of those machines. Please, never stop caring about them, they are precious pieces of history. Thank you very much!

[@jonord]

Oh, this brings back memories. Still wish I could have kept the PDP-11/23 that I had access to 30 years ago.

[@chriswareham]

You might want to check the PiDP -11/70, a recreation of the control panel with a Raspberry Pi running the simh emulator. I built one during the COVID lockdown, and it's great fun to use. There's also a project to recreate the PDP-11 guys on an FPGA to replace the Pi part of the system.

[@jonord]

@@chriswareham Yes, have considered, but there's something with working with the actual hardware that appeals to me, not so much playing around with the OS and so on.

[@williamhaffelder7032]

That mobile terminal is just absolutely gorgeous!

[@sahasrahla7]

You explained how this power supplies works so well, even with my high school knowledge about electronics I got the gist of it! Awesome video, can't wait to see you restore that gorgeous portable terminal!

[@richardabrown]

Well done on getting it to work I only watch to the end to see the rabbit and that is one cute rabbit

[@andymcgarty3099]

Superb work, well done that man. Looking forward to seeing this develop as you add drives.

[@nielswebster34]

I love to stay around! Sweet little animals at the end, a nice recap and future plans, and sometimes a really colorful suprise!

[@winstonsmith478]

That ADDS Envoy terminal looks SO 1970s retro.

[@null_carrier]

Just wanted to say 'thank you' for making these videos.

[@button-puncher]

I find the physical terminal hilarious. Having only used software terminals my whole life. A huge dedicated box with monitor and keyboard to only view and generate serial data. I love it. Congrats on getting it all running. :)

[@Renville80]

That had to be SUCH a good feeling when that text popped onto the screen! Super!

[@JonathanSwiftUK]

Epic. Superb job. DEC PDP11s were the first mini computer I used. Quite nostalgic.

[@binarydinosaurs]

Yes! Congrats Dave, a good job well done. Those ADDS terminals are lovely things indeed, looking forward to the rest of the work :D

[@PeterDoingStuff]

That portable terminal is just so awesome, gratis colors and just insanly cool😂❤

[@AB-Prince]

for pulling out components, I find a small metal crochet hook to be ideal.

[@jeromethiel4323]

If you can find a set, dental pics are amazing for small, tight spaces. Care must be taken, however, because they are metal and conductive, you need to make sure everything is dead before poking around. Short across an undischarged capacitor can make for a few moments of excitement, and perhaps more repair work than when you started... ^-^

[@andrewsteppan1868]

@@jeromethiel4323 I have a couple of dental pick sets for exactly this and can attest they are effective! I am one of "Today's Lucky 10,000" and have found "PEEK" plastic pic sets exists - non-conductive and heat resistant to 500F! (McMaster-Carr really has everything)

[@d614gakadoug9]

Crochet hooks are useful for circuit tracing after a computer executes an _HCF_ instruction (halt and catch fire). An ancient PDD-8 (as a TSS-8 - it had 16 teletypes for user terminals) in my department executed that instruction. The backplane for the CPU was all wire-wrap and something around 2 feet square. This resulted in a bunch of burned wires. I tracked them all down by visual inspection, using a pair of hooks to gently tug on wires to find their routes. Iirc, there were only two that were badly burned but that damaged insulation on a number of others that were in contact (these were 28 or 30 AWG fluoropolymer insulated wires. Again, iirc, it was a memory driver board that that had actually failed and caused the damage to the wires.

[@johncloar1692]

I always watch till the end. Nice work on the power supply I have done a lot of power supply in the past and have never run across this type of supply. Nice work!

[@ThomasBaxter]

That terminal is ungodly sorts of gorgeous! Me wantee!

[@frankowalker4662]

Great work on the PSU. That terminal is georgeous !!!!!!! Can't wait to see it in use.

[@andymason8315]

Thanks for your always great videos.

[@shawnerz98]

Congratulations, Dave! Good to know you got it working!

[@rastersoft]

That bunny is BIG! 😀

[@TubeTimeUS]

excellent work and congratulations! tenacity is the key to troubleshooting.

[@KeritechElectronics]

Indeed it is. I spent two frustrating weeks sitting over a baaaaadly noisy power amp in a Harman Kardon 730 and pinned the problem down to the differential pair transistors, replaced all of them to prevent the same thing from happening in the other channel. Very satisfying.

[@simonabunker]

That was an epic power supply journey! Glad you managed to work it out. Love your enthusiasm about these old machines!

[@bikeforever2016]

Awesome work and result. That terminal is gorgeous.

[@OpossumPiper]

oooo! YELLOW, ORANGE, and BROWN!!! I can't wait to see it up and running!

[@marknesselhaus4376]

Fantastic. I always watch till the very end as I like to see what your fur buddies are up to 😀

[@gnustep]

I always watch until the end buddy! Great news. I love your videos. I grew up with some of these machines so it’s great to see them coming back to life! Please keep it up!! 😊😊😊

[@eboyd53]

You bring back memories long forgotten. I actually used one of those luggables before, talking about headache from eye strain.

[@bradleyphillips5254]

Loved the video, thanks!!

[@mattbastable1942]

Love the Centurion backdrop but that wonky shelf bracket is driving me nuts :o)

[@UsagiElectric]

Which bracket are you referring to? The Data620 in the opening has a bad rail on the Core Memory unit, which is why we have that unsightly gap. I'm still working out how best to solve that, but the Centurion system is pretty neatly put together I think!

[@Fleeeeg]

Why did you have to point that out, now I can't unsee it

[@colinstu]

@@UsagiElectric 16:55 I think that middle bracket of the three seen on that shelf on the top right... it's a bit cockeyed xD.

[@johnm2012]

​@@colinstuOh, for pity's sake...

[@colinstu]

@@johnm2012 yeah I didn't even notice. I'm gonna keep ignoring it.

[@johnwest7993]

Old Blue! I used one of those terminals while sitting beside the turret of an M-47 US army tank rolling through a field in Colo. Spgs. CO in 1974, while trying to make the autonomous tank's 8080-based control computer play nice and not toss me off and run me over. The very first of Skynet's little helpers, and I helped bring it to life. Good times.

[@Nichetronix]

One of the best things about your channel is your enthusiasm. Brings a smile to my face to see your victory dances when you get some ancient piece of hardware working again!

[@boredwithusernames]

Excellent result, your enthusiasm is very infectious and I was applauding when that power good light came on. It's good to see such a classic machine running again after all these years. Looking forward to the next instalment 👍Btw I watched all the way to the end so I am a member of the 30% club 😁😎

[@rivimey]

I'd love to see you get a very early version of Unix running on this. We all know where that path took us, but few know where it started.

[@edgeeffect]

I saw a PDP-11 Unix exhibit on KZbin just a couple of days ago and, even though I'm quite a Unix fan, I thought it was a terrible waste not not have RSTS/E on it.