TRS-80 DT-1 Refurb Pt1: Analysis and Electronics |

[@TechTangents]

Part 2 is available here: kzbin.info/www/bejne/gZjEdISarbdmqJI

[@Lee_Adamson_OCF]

Your bodge wires are exactly the same as mine (except for the color lol). I bet it was either a factory thing or a technical service bulletin. I tried to reverse-engineer mine a bit; pretty sure it has something to do with the parallel printer port enable circuit, but there is something extremely weird going on with that MC1489. I recorded a video on the subject, which is in the process of encoding. Probably won't be able to upload it until tomorrow night though.

[@Lee_Adamson_OCF]

Also, that LS374 underneath of the printer port is supposed to be a '373, according to the schematic. I see that yours is also a '374. Mine shows evidence of having been desoldered and replaced at some point.

[@Lee_Adamson_OCF]

Also, I have a cut trace on the back of mine, to separate two lines of a 3-in NAND that were tied high, with a 4.7k pullup on the one with the cut trace. Then the bodge wires on the front tie an unused output of a 3-8 decoder to that input, through a level converter gate on the 1489 (which is what I don't understand) and then through an unused gate on a 7406 inverter.

[@Disappearinginc]

It's great to see our old DT-1 getting the love it deserves! Clearly it found a good home with you.

[@ShadeAssault]

I love these old Tandy PCs. Been looking for a TRS-80 myself. I frequented the RadioShack in my hometown while in Middle/High School when my friend and I were modding consoles, then I worked at RadioShack as an assistant store manager for about a year until they went under. I hated what they were at the end, but man do I still have nostalgia for their stuff. Keep up the great content and thanks for showing these old systems.

[@staticfanatic]

i love how you make a concerted effort to show that clock rolling a digit over whenever it's on screen.

[@raggededge82]

19:10

[@tombarber8929]

except 22:53

[@SyphistPrime]

A vintage terminal to your modern server? That sounds awesome.

[@happyguy5025]

Your editing or whoever edits this is really good, like 10/10 good.

[@eduardoavila646]

It's in fact him who does it! And he even showcased his edditing setup and his edditing server (and upgrades for it).

[@CelGenStudios]

Now that I'm thinking about this terminal, I might very well of been responsible for the broken edge connector. We had multiple units that came in and we sold most of them but I had to check all of them and yes those connectors were EXTREMELY stiff and I KNOW more than one broke trying to wiggle it off. Don't tell my old boss!

[@TechTangents]

Tsk Tsk, at least I was able to get working again.

[@tickertape1]

Celgen where have you been I miss your videos

[@ToTheGAMES]

@@TechTangents Spoilers 😥

[@ps5hasnogames55]

well have* not well of. learn how to speak english chud

[@riffraff60]

The low serial may be because it's from Canada. From what I remember they used their own serialized stickers that didn't necessarily match production serial numbers.

[@MichaelAStanhope]

If memory serves, Radio Shack used to use these for POS terminals in their stores in the 80's and early 90's. When I worked there in 1996 we were using Tandy 4000 computers that were configured as terminals. The mainframe really wasn't updated in years. Wouldn't suprise me if thats what this one did in its life.

[@SeltsamerAttraktor]

You can probably tell from the burn in on the CRT

[@IrishCarney]

Makes sense because I remember Radio Shack unloading , at fire sale prices, all the Model III computers they had been using, one per store, for POS and for sales reporting purposes. The ads didn't mention what the replacement machine was going to be for in-store use, but maybe it was the DT-1.

[@Ramsis-SNES]

#SepTandy? Love it! ^^ Great restoration project, can't wait for part 2! Please keep up the good work! :D

[@miszcz310]

24:13 next to this white element (buzzer?) You have loose screw! Somehow glued? Anyway once I saw I couldn't unseen it.

[@nekomancerUwU]

I was about to comment on that too. I noticed it at 23:24

[@GeoffSeeley]

Noticed it too!

[@freednighthawk]

I saw that too and came down here to comment about it.

[@unmountablebootvolume]

I saw it too! It can also be seen in 23:26.

[@edwinmoney619]

My high school had about 60 or 70 TRS-80 (Trash-80 we called them), even had a massive 10MB HDD for network storage... Finally co-wrote a grant and got them all replaced with Pentium computers and Ethernet networking with a Novell NetWare server for online storage... Even managed to integrate the Mac network that was in place before the rollout....

[@HuntersMoon78]

Everyone called them (Trash-80) not just you.

[@Saboteur709]

RIP Eddie Money

[@pentiummmx2294]

I liked the Apple IIe better.

[@ColdRFusion]

At least the fan didn't cause any permanent damage to the case, no holes to deal with. Love the repair work on the connector, hope it works!

[@Starchface]

First-time viewer, first-time caller. Fantastic video dude. Love this stuff from back in ye olden days. Indeed, power supplies of the era were often fixed to a specific input voltage. In the pre-globalized world, products were intended for a specific market. A European version, for example, would have likely had a different PSU from the North American version. Today, with ultra-cheap universal switching PSUs, that makes little sense. The only difference is the plug on the line cord. The Apple II was an exception. Its switching PSU-very uncommon for the time-could be used on either 120 or 240V.

[@brycelynch2138]

The in-picture tight zoom on your voltmeter was a really nice touch - I like it.

[@madmaxgrey]

hey AkBKukU do you have a TRS-80 model 100 if you don't i have one that's slightly used but still have the box and the manual for it in really good condition. My uncle bought it when it was first released in 1983. when i go home in a couple months i can see about sending it to you if you don't already have one.

[@monsalai]

You're going to want to email him, or message him on Discord

[@TechTangents]

I don't have a Model 100 and am definitely interested in it! If you do want to send me that one email me to talk about it more. I've tried reply to this three times now with the email address but apparently YT is blocking my own comments with that. You can find it in the channel description though.

[@brianv2871]

Love that Tandy. I'm totally with you on the keyboards. My TRS-80 Model 4 also needs the keyboard disassembled and either cleaned or possibly add silver conductivity to the pads, but because it's so much work, I've opted for the 'Press Keys Harder/Longer' method instead. :) At least I have a desoldering station now, so it shouldn't be quite as bad when I get around to it.

[@C6438911]

Personally I don't see and don't have any experience with these kinds of computers, but it is fascinating nonetheless. Amazing video once again and thank you very much for sharing! My very first computer I owned was a Commodore VIC-20. I was about 10 years of age back then.

[@泉こなた-t2q]

In Japan they have 50Hz and 60Hz. Maybe the Psu was also sold ther?

[@mattparker9726]

I love the boxed pod games in the background.

[@Dreams_Of_Lavender]

That Wyse terminal in the ad is gorgeous.

[@johneygd]

Thanks for showing this,you do have alooot of technical dkills & knowledge ,but i only wish you called it part 1 sothat we can prepare ourselfes for part 2.

[@santi308]

-9v on a -12v rail is not good. Change the caps, three of them looks bad on top cover.

[@theretrospector4926]

Have the same opinion. Those old caps start leaking without clear signs of bulging on the top. -9V on -12V rail might be first sign. I do not know the schematics, but if the whole thing only uses 20W, I would change the power supply with a small modern one. You have enough space in that case for 2 (modern and original). Although it might be hard to find a small one with a -12V power rail.

[@Sheevlord]

16:00 This capacitor isn't actually doing anything for the power supply. It's there as a part of the EMI filter that prevents switching noise from the PSU getting into the AC power outlet and potentially interfering with other devices (mainly AM radios) powered from the mains. Omitting it wouldn't hurt the terminal in any way.

[@InfiniteBrain]

I've found several different system power supplies that include footprints for both size X capacitors. Makes it pretty nice because everything will fit smoothly regardless of which options you use.

[@TheGabri00]

20:15 he said “ssweet” and the fucking clock rolled, most satisfying thing ever

[@bennetfox]

Where is part 2? I must see this thing work!

[@rricci]

Maybe editing itas we speak (type)? I liked the TRS-80s when I was younger. Never had a chance to play with a Model II.

[@FaithyJo]

20:10 good to see you rethink putting your hand on a hot, unshielded power supply

[@linksmith1057]

When you turned over that micro controller board I believe I said out loud, “holy kludge wire Batman!”

[@TinWhisker]

The heatsunk diodes are 'Avalanche' diodes, similar effect to Zener, but more for circuit protection by 'clamping'/'crowbarring' current during over-voltage conditions than the Zener approach of regulating the voltage nearer the target voltage.

[@tim0steele]

Ah, the "Reefer" caps. I had one let go in a sewing machine and one in a food mixer. They get everywhere!

[@jtsiomb]

The line filter cap has nothing to do with protecting the device itself. It's just there to prevent the device from putting out interference on the power lines that could affect *other* devices on the same power line.

[@MartenElectric]

Great job troubleshooting so far, may I have one suggestions? change all electrolytic caps on PSU and lift these 2W resistors off the PCB. Will help a great deal from completely burning FR4. Thanks for a great vid as always!

[@tickertape1]

Audiophile Vintage This is a common misconception I have many old systems and all the electrolytics are fine

[@MartenElectric]

You are absolutely right, you do t have to change them if they measure fine, but as a precaution you should. Especially for these TOTL vintage hifi keepers I’m changing all el caps with higher temp value caps when necessary

[@KingPepper41]

Did any one else notice the large Capacitor wobbled, when he touched it @14.47, hope he re-soldered that.

[@8bitbubsy]

The solder is most likely fine. Some caps can still wobble a bit despite being properly soldered down.

[@OjStudios]

All of those caps should be changed in something this old.

[@Spider_Rico]

You, sir, are obscenely interesting. My house could have been on fire and I wouldn't have noticed. I couldn't pull away from this video.

[@WhatALoadOfTosca]

So can't wait for pt2. Thanks for sharing.

[@hazardsoftech]

Always stoked seeing a new AkBKukU video!

[@ropersonline]

23:00: What's with the screw next to U6 and the, I dunno, is that a piezo speaker?

[@brandenrobinson9411]

Probably. I had a DT-1 once upon a time and that was the only part that was intermittent. I never had the thing open. But these had a buzzer/"bell" because that was required functionality for a terminal. Not so much for the TRS-80 Model I or Model III, where your only option for sound was via the cassette port. Well, okay, for the Model I you could also put an AM radio near the machine and experience sound synthesis via RFI. Games were actually programmed this way. The FCC wasn't too thrilled with that, which is why the Model I was withdrawn from the market.

[@sadmac356]

I have to laugh at the fan placement because it's so ridiculous

[@douro20]

There are a good variety of CRTs which will work in there- the JIS version of that CRT, which should be a bit more common, is the 310GNB31.

[@ElectricEvan]

23:27 what is with the tiny screw shorting out the pins on U6?

[@pcuser80]

I used to have one, but the Y key was broken. Very difficult to save the settings...

[@omysan]

I would like to see that fan running just for giggles ..and sound of course.

[@brycelynch2138]

Do you think some Sugru on both sides of that chipped-off piece of PCB would further reinforce the repair?

[@Stefan_Payne]

The Input Filtering is, while called input filtering (X&Y Caps + the Coils), not to filter the Input but to filter the crap coming from the PSU to the mains. So yeah, you can remove that without issues, if you have good AC coming in and not use 10 of them at the same time. And get some Desoldering Wick or braid... PS: Its -12V/0,1A and +12V...

[@luha628]

Awesome video!

[@hesterhenrietta261]

This is so gnarly, I love it 💐

[@780tech]

LOVE your Videos ! p.s. Bottom of my Model 4 Does NOT have the metal mesh screen pieces

[@solarbirdyz]

Working with either 50hz or 60hz but only 115(range) voltage means it works in throughout Japan, which has 50hz in the east, and 60hz in the west, all at the same voltage. I bet the maker also sold that power supply there.

[@Darknecros7]

Yeah, the 50hz would be so it’s usable throughout Japan, which as the above person said, has 50hz in east and 60hz in the west, but 100v throughout.

[@bryandepaepe5984]

JB Weld epoxy will provide a much greater bond than crazy glue and can be sanded down to form any shape needed.

[@eduardoavila646]

I see you watch project farm too?

[@Hurricanelive]

First comp was a model 4. Was pretty nice for gaming. Upgraded to a Tandy 8088 for a few years till I got a proper Gateway P166 and WOW that was the shiz for me!

[@masterroot24]

AkBKukU: "It's just two screws, right?"... Me: "AkBKukU, when will you learn?!"

[@filminginportland1654]

My first computer was a Model 4 back in the early 90s, a couple years before I got an IBM XT with 2400 baud modem that let me get on the internet (shell only of course). Had a lot of fun messing with it, but it didn’t have any games. Got it from a relative who sold insurance, and it only had stuff like Lescript and VisiCalc; not terribly fun for a 12-year-old. But at least it had a printer. Had a 300 baud acoustic-coupled modem I found that I tried to use as well, but didn’t have any terminal emulation software with which to use it. Wouldn’t mind playing with one again. Any ideas if there were games made for these models? My understanding is they were for business and the TRS-80 CoCo was the one for games.

[@captainboing]

The mesh could easily be part of some environmental shielding. We had to do the same with kit we sent to the tropics to stop bugs climbing inside

[@Psychlist1972]

If the wire mesh is not all grounded together, it's not for shielding. Presumably it's for dust. Interesting that they'd bother with that with no stock fan in the case.

[@WolfKenneth]

Cool idea 👍 think about doing month dedicated for Amstrad/Sinclair

[@draggonhedd]

[@omysan]

That is a great ideea,but as a quick note I'm sure i ve heard some people say that doesn't always work with all modern psu,s due to the way the do the converting.Just be safe out there.

[@theannoyedmrfloyd3998]

I spent 3 hours cleaning out a laptop keyboard once. A DT-1 keyboard would be fun! You should reflow all the solder for it being so old. Put a piece of flat metal in the solder side to reinforce that, but use epoxy on the other side to strengthen the bare PCB side.

[@substance1]

Nice serial terminal. I'm sure it had many great years interacting with Unix and/or mainframes and mini computers.

[@brentboswell1294]

If it didn't do VT100 emulation, it didn't survive very far into the Unix era...

[@Loenne555]

Fan, wire mesh, multiple wires soldered in... First casemod and first modchip in computer history discovered.

[@stevesmusic1862]

Nice Barbies you sent to LGR, Shelby :)

[@JonTheGeek]

Wow dodged the line filter bullet, good job man xD

[@boelwerkr]

Just a first guess. The fix looks like a correction of some bus-timing problem. An inverter is involved a flipflop and some bus driver. But just a guess. I can't see the ICs good enough to make out the details. And it's done from someone who had the schematics. EDIT: Use some small pieces of paper towel soaked with superglue as braces to stabilize the crack.

[@timfountain98]

You posted a picture of an online 1984 main cpu board. It's very possible the bodge wires were on the back.... Just a thought.

[@Mikeywil0003]

I wonder if that board with all the bodge wires was a factory refurb that went into an early unit that went in for a warranty claim?

[@tmburns4]

Great video. I see some of the chips are socketed. Did they come that way from the factory, or does that indicate that someone has done some work on the board?

[@smalltownMainer]

with my model 3, i got lucky with the keyboard, only the #9 key on the right keypad was not working, i re soldered those two pins and now it works. it has two power supplies so i had two of those filter caps to change, and mine also has to heat sinks.

[@KevRalph]

We still had a couple of "dummy" terminals remaining when I first started in the business world in the mid-90s... And they finally disappeared and were replaced by pc-based 3270 emulators..

[@TinkerbatTech]

I see comments on that neg-12 voltage being low. These supplies are meant to be tested under load, the neg 12 isn't really regulated, just zener clamped IIRC. Once you're pulling an amp or so from 5 and +12, it'll probably pop right up to 11-13v just fine. I ran a computer repair shop back in the '80s, Trash-80s were a favorite. Converted soo many model III and 4 cassette models to floppy based back then, adding drives, controller and power. Bought a couple 100 of this style P/S when Osborne went under, kept me in rent for quite a while..:) Still have a few parts and bits rattling around. And a few model 100s.. Loved those things... Stu

[@TinkerbatTech]

Oh. And those little gray diodes soldered to those heatsinks are tough little buggers. Can handle 3A + and don't think I ever saw a bad one...

[@Nukle0n]

They might've started a new serial range per year?

[@WilliamHostman]

The screen is to prevent bug entry, a problem several friends of mine had with their Model 1's.

[@CattoRayTube]

That ending felt weirdly like a cliffhanger haha

[@charlesmurphy1510]

I bought a model 4P which is the portable model 4. It cost around $4,000 at that time circa 1982.

[@wesstatzer163]

love the old flip clock bro

[@kaylaandjimbryant8258]

might i recommend a hakko fr-301? i love mine!

[@GuybrushThriftweed]

Why do I always love your vids lol :)??!!

[@MrLurchsThings]

Oh cmon, disassembling the Model 3 and 4 isn’t *THAT* bad (cough, splutter). I had to do the KB on my Model 3. The only worse keyboard I’ve had to work on is my Microbee. Righto, time to do the last edit on my first video. Stand by....

[@vwestlife]

The trick to safely opening a Model III or 4 is that as you start to lift up the cover, look into the gap that is formed above the top floppy drive to make sure the CRT isn't going to snag on the wires going to the main logic board. Usually those wires are tied well out of the way, but sometimes if a previous tech had worked on the board, he might have left them loose.

[@MrLurchsThings]

@@vwestlife Yup - there is certainly a knack to it. Although thats not to say there isnt still a moment of "Please clear the tube, Please clear the tube, Please clear the tube, Please clear the tube, Please clear the tube" :)

[@Lee_Adamson_OCF]

I just cracked mine open last night. It has bodge wires all over, too. Video will probably get posted late tonight, if you are interested.

[@TzOk]

Solder blob will break. You have to reinforce it with a piece of copper foil or even with a left over from resistor "leg".

[@eduardoavila646]

Mostly not, probably his solder has lead, and it wont have many vibration and that much of a temperature change.

[@TzOk]

@@eduardoavila646 I can't agree - there are significant temperature changes inside the case, remember that next to this board there is a CRT, which produces a lot of heat. You can also hear the hissing sound of working CRT, that means there are vibrations - they came mostly from the deflection yoke. This is 50/60HZ + 15kHz. They are tiny, but constant.

[@eduardoavila646]

@@TzOk Yes significant, but not enough to make a solder expand and retract that much. I was talking about the whole system going 60°c and up.

[@SkyCharger001]

I just noticed that there are two other numbers on the bit showing the serial number, perhaps it's a revision specific count.

[@coondogtheman]

Nice alarm clock, I had one just like it, made me late a number of times then I bought a cheap sony dream machine in which I still have the guts of it and the radio still works. No clock though. Could you remove the logic ground wire(the one where the connector on the board is broken) and just solder it to a point on the board that is connected to the pin that was broken?

[@bramvandenbroeck5060]

We had one of those in the local library way back in the day

[@eeromikkola2379]

0:39 Hey Vsauce AkBKukU Here

[@williamchow1624]

Baking Soda on the glue and maybe solder a copper foil on the trace for reinforcement?

[@SenileOtaku]

I've thought maybe a wire to the ground plane (or whatever it's called) and another to the back side of the harness plug (with some connector to allow it to be unplugged)

[@draggonhedd]

for the broken off tab, glue something like a piece of tissue paper to the back side of the broken tab with super glue. it will add strength.

[@juddsandage]

I do have a TRS-80 Model III, any suggestions as to what to replace first? cap wise? it has not been touched in probably 25-30 years. I haven't even opened it, its just sitting on a shelf gathering dust.

[@BlakeGJ]

First be super careful when you open it. Go slowly and look inside as you open it to see how it lifts to clear the board. The neck of the CRT can be broken off by the mainboard. Video Display Corp has NOS tubes if that happens. Then replace the caps on the power supply. You should go to vcfed org for more help before you start.

[@iceowl]

Radio Shack had a reputation for reason back when they made their own stuff.

[@pixelflow]

Oh cute the case even has the drive bay openings.

[@retro8263]

Perfect Click without any doubt.

[@233kosta]

Line filter caps are mainly there for noise suppression - stop it backfeeding interference through your house's wiring (which at that point becomes a giant antenna). Removing yours won't kill anything, but it will also most likely demolish any hope that PSU had of ever being FCC compliant. I'm pretty sure you can get filtered sockets (or extension leads), and I'm quite certain that you can just get inline filters to add to the power line yourself, but you're 100% on this - it's best to just replace the bad cap, do the job right.

[@Godzilla_Jesus]

Heat Synced Diodes was the name of my high school garage band.

[@richardkelsch3640]

Contrary to the claims of the uninformed, rosin flux is non-corrosive when cool. That is why it is used in electronics. Flux residue may be ugly, but it will not cause problems at room temperature.

[@clangerbasher]

I remember these............. But the cool one is the teletype with the acoustic coupler..........

[@brentboswell1294]

Radio Shack had an acoustic coupler modem available...No reason it wouldn't work here for the 1980's working at home experience! 😉

[@clangerbasher]

@@brentboswell1294 This beauty...... www.trs-80.org/wp-content/uploads/pt210.jpg

[@brentboswell1294]

@@clangerbasher that's a beast! This is what I was thinking of.... www.computinghistory.org.uk/det/13105/Tandy-Radio-Shack-TRS-80-Acoustic-Modem/ you'd have a Hayes smart modem on the other end, with software that would answer the call on a dedicated line, and once the connection was established, you were working over a 300 baud connection to the office. Basically, a really expensive, long, and slow rs-232 cable 🤣

[@MaximRecoil]

I would have just soldered a wire to the trace that connects to the broken piece of the card edge (looks like there's even an unpopulated through-hole just above the broken piece that you could solder a wire into), then spliced another wire into the edge connector harness, and connected the two wires with a Molex connector. No worrying about a fragile repair doing it that way.

[@EdwinNoorlander]

Can’t wait for part one.

[@unmountablebootvolume]

I found a .15uf rifa firecracker in my boiler mixing valve wich was used as a run cap for the tiny synchronus motor that was about to blow up and was already cracked and about to go BANG! So everyone with an old boiler with a digital controller should check not only their trs 80 power supply but also the boiler controller and it's peripherals for rifas.

[@RE1974]

Hope to see you at Tandy Assmebly!

[@TechTangents]

Unfortunately I won't be able to go, I've done a fair bit of traveling this year already and don't have the budget for it. I'm hoping next year I can fit in going to more computer meetups, so perhaps then!

[@dodgydruid]

Wow, that is so like an old Sperry Univac data terminal of the same era, cut my teeth programming on an ol' Sperry til I got kicked off the course for hacking the college's mainframe which was linked to the county council's even more interesting mainframe, happy days of a misspent youth ;)

[@jaykoerner]

Either the serial number rolled over or it was the 41 in either that run or that year.

[@DS-es7id]

i can only imagine the direction my life would have gone if my trs80 color programmable computer would have not overheated in the middle of every program i ever wrote. I think it was Q-basic? or color basic. It hooked up to duel dial color television. It needed a fan BADD!