The PDP-11/23 Plus Works!

[@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.

[@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 🙂

[@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”.

[@darkwinter7395]

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

[@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.

[@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

[@nutsnproud6932]

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

[@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.🤣

[@michaelpelley2815]

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

[@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!

[@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!

[@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.

[@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.

[@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.

[@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.

[@hangonsnoop]

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

[@peterfireflylund]

That far from Cardiff?

[@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

[@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.

[@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.

[@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.

[@sn1000k]

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

[@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.

[@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).

[@vicroc4]

Yeah, as soon as I saw that the input was so low, I questioned whether or not the regulator was actually the issue.

[@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.

[@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!

[@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 ?

[@dickot]

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

[@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!

[@andysmith8649]

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

[@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.

[@smrp1984]

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

[@BBHexKey]

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

[@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!

[@Jim-be8sj]

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

[@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.

[@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.

[@muadeeb]

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

[@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 👍

[@AerikForager]

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

[@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.

[@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.

[@mikeziniti]

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

[@annihilatorg]

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

[@vicroc4]

I love the sound of the fans spinning up when you turn the power supply on.

[@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!

[@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 :)

[@kensmith5694]

You missed an important component in your description of the 7805 based regulator. I will describe that part of the circuit from memory and hope I get it correct. The emitter of the "pass transistor" goes to the junction of a diode to ground and a large inductor to the +5V. When the pass transistor is on, the emitter is at the +24V-(a bit). Current starts building up in the large inductor. Think of this current as ramping up from zero until it is more than your load current. When the inductor current is more than the load current, the output capacitors start to charge up. At some point (more on that in a moment) the 7805 stops trying to pass current so the pass transistor switches off. The diode I mentioned previously is now conducting and the current in the big inductor is ramping down. At some point, the voltage goes low enough that the 7805 decides to act again. Now for the "more on that" Note the resistor from the emitter of the pass transistor to the GND leg of the 7805. When the pass transistor is on, this slightly raises the voltage on the GND of the 7805 so that it sees a lower voltage from its output to its ground pin. This makes the 7805 slam on extra hard trying to get the voltage up to 5V. This means your pass transistor will be biased solidly on. When the pass transistor finally turns off, the resistor lowers the voltage on the GND of the 7805 so it sees a slightly higher voltage and stops delivering current.

[@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.

[@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!

[@dmatking2000]

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

[@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~!

[@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.

[@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.

[@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.

[@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!

[@makerofthingsunique]

I always wait to see the rabbit 🐰

[@esra_erimez]

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

[@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. :)

[@jaystechstuff]

just want to say: well done! it's kind of entertaining to see that old PDP-11 been revitalized 👍

[@drozcompany4132]

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

[@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.

[@southDutchMan]

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

[@kahvikissa_]

love how colorful that portable terminal is

[@eboyd53]

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

[@SignalDitch]

That Envoy is a thing of beauty

[@ckworton]

Holy H! The colors of that ADDS Envoy. 😂

[@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!

[@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!

[@Renville80]

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

[@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.

[@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.

[@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.

[@williamhaffelder7032]

That mobile terminal is just absolutely gorgeous!

[@therealjammit]

Q9 in the crowbar circuit is a programmable unijunction transistor (PUT). It's used as a voltage controlled switch to accurately and decisively trigger the SCR.

[@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.

[@OpossumPiper]

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

[@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!

[@ShellacScrubber]

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

[@richardabrown]

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

[@colinsmith6480]

love the Portable terminal, great to see your work on these machines, I used a lot of similar machines when i first started work , and they were so cutting edge then !

[@skfalpink123]

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

[@PeterDoingStuff]

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

[@DanelonNicolas]

this is insane. it was amazing to see that machine back to life. watched til the end, haha

[@AndersNielsenAA]

I love the keys on that terminal ❤ Orange “rub out” ❤

[@ThomasBaxter]

That terminal is ungodly sorts of gorgeous! Me wantee!

[@erueratait-jamieson480]

That terminal is such class, how good would the PDP look with matching colour scheme!? Brown panels, beige trim, and orange faceplates 🤤

[@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!

[@adulaney2004]

That is definitely an interesting power supply arrangement, and that ADDS Envoy is awesome!

[@null_carrier]

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

[@mickre-fuses]

Another excellent video. Thank you for sharing. By the way, I'm one of those that watch your videos right up to the end. Sometimes there is an upside to OCD. 🙂

[@winstonsmith478]

That ADDS Envoy terminal looks SO 1970s retro.

[@musiqtee]

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

[@LeonDerczynski]

woah, who isn't staying til the end?! don't you want as much of this channel as you can possibly get!

[@JonathanSwiftUK]

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

[@frankowalker4662]

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

[@jamesross3939]

So cool the moment it works the first time!!! Took a lot a patience man! WTG! Edit: the excitement when you got it working on the terminal is contagious... yayyyy!!

[@LittleDancerByGrace]

I always stay till the end for reasons exactly like that. You just never know what kind of plot twist will happen...

[@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.