Using our new diagnostic ROM to fix a TRS-80 Model III!

#trs-80 #repair
The TRS-80 Model III is fixed! As you saw in part 1, I was really stumped by the problems this board had -- so I reached out to friends Frank and David about making a diagnostic ROM for this machine. I posted a companion video on the second channel taking a deeper dive to the ROM, I recommend you watch that after watching this video. The repair showed off how even someone as "seasoned" as me can make fundamental mistakes in the troubleshooting process.... So watch to find out what mistakes I made, and what it took to get this machine running again!
Thanks for Frank IZ8DWF and David KI3V for making the diagnostic ROM a reality.
Part 1: • TRS-80 Model III garba...
Part 2: This part!
Diagnostic ROM deep dive companion video:
• Let's talk: Our brand ...
--- Video Links
TRS-80 Model 3 (and Model 1) diagnostic ROM:
github.com/misterblack1/trs80...
2364 adapter PCB:
www.pcbway.com/project/sharep...
Frank IZ8DWF's channel: (for really amazing repairs)
/ iz8dwf
When good caps go bad: (t-shirt donated by Jesse)
www.teepublic.com/t-shirt/241...
Adrian's Digital Basement Merch store:
my-store-c82bd2-2.creator-spr...
Adrian's Digital Basement ][ (Second Channel)
/ @adriansdigitalbasement2
Support the channel on Patreon:
/ adriansdigitalbasement
-- Tools
Deoxit D5:
amzn.to/2VvOKy1
store.caig.com/s.nl/it.A/id.16...
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.com/products/digi...
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.com/item/33000...
TS100 Soldering Iron:
amzn.to/2K36dJ5
www.ebay.com/itm/TS100-65W-MI...
EEVBlog 121GW Multimeter:
www.eevblog.com/product/121gw/
DSLogic Basic Logic Analyzer:
amzn.to/2RDSDQw
www.ebay.com/itm/USB-Logic-DS...
Magnetic Screw Holder:
amzn.to/3b8LOhG
www.harborfreight.com/4-inch-...
Universal ZIP sockets: (clones, used on my ZIF-64 test machine)
www.ebay.com/itm/14-16-18-20-...
RetroTink 2X Upconverter: (to hook up something like a C64 to HDMI)
www.retrotink.com/
Plato (Clone) Side Cutters: (order five)
www.ebay.com/itm/1-2-5-10PCS-...
Heat Sinks:
www.aliexpress.com/item/32537...
Little squeezy bottles: (available elsewhere too)
amzn.to/3b8LOOI
--- Links
My GitHub repository:
github.com/misterblack1?tab=r...
Commodore Computer Club / Vancouver, WA - Portland, OR - PDX Commodore Users Group
www.commodorecomputerclub.com/
--- Instructional videos
My video on damage-free chip removal:
• How to remove chips wi...
--- Music
Intro music and other tracks by:
Nathan Divino
@itsnathandivino

[@Vidfavne]

This was more entertaining than anything I can currently find on Netflix, Amazon Prime, Viaplay or Disney+

[@alexviralata1356]

Bro, this was better than those south american soap operas that my grand mother used to watch XD

[@simonlawson2236]

Stranger things was pretty good.

[@roberttalada5196]

And yet we still don’t pay for KZbin premium

[@mdkramster]

Maybe it's the vodka!

[@rommix0]

Well yeah. The streaming services are so scripted and calculated, yet with people like Adrian and LGR it's not too scripted and just casual enough to connect with the audience.

[@thepresi2]

I just bought a not functioning TRS-80 Model III for repairing. These videos are to me one of the most precious things in the whole world right now. Thanks for doing this!!! (I'm a happy Patreon)

[@infinitetape]

As someone who's worked on Bally Midway machines (like Tron), those cheap ribbon cables go in the trash immediately, even if they appear to work. They're just too much of a liability.

[@billfusionenterprise]

That cable reminds me of something at work , where a connection on a signal tranformer was loose solder wise. Got voltage (continity) but could not do any current. it's one terminal was broken solder inside

[@SonicBoone56]

Replace them with kapton flex cables or an actual ribbon cable. This 70s paper crap goes in the garbage.

[@bentucker7280]

might pass dc current, but a high frequency square wave with no crosstalk: Some of the time

[@Bobbias]

I don't deal with old electronics like this, but I definitely did not like those cables at all. I can't say I'd have caught this sooner, because frankly Adrian knows more about these machines than I do, but it reminds me of how it's often a good idea to preemptively replace capacitors when there's a chance they might be bad. Still, it's great that this has lead to a diagnostic ROM being created.

[@Grunchy005]

Signal Generator @ 2 MHz and oscilloscope, how does the ribbon mangle the communication? We want a follow up!

[@AstroBoyAU]

It's always the simple things, Having owned a TRS-80 from new. Modifying it, building the LNW-80 interface and writing heaps of machine code back in the day. I was so involved back then that I also acquired a KAYPRO-10 which was a Z-80 machine with a 10MB HDD that had failed. Replaced the drive with a 20MB drive, designed and built an EEPROM board that I could switch addresses and enable and disable writing to it etc. Re wrote the ROM code to support the 20MB HDD into an 8MB / 8MB and 4MB partitions running CPM. Built a high resolution graphics interface for it (640 x 400) extended the code in the ROM to support accessing the new graphics and it was a good fun project. Sadly I don't have the machines any more But I learned alot about digital electronics in my youth.

[@retrozmachine1189]

I modded my long gone MIII to the extreme with all sorts of homebrew including an 8MHz Z80H, overclocked of course.

[@mal2ksc]

I think I'd run permanent bodge wires on the back and never have to worry about the ribbon cable again. The homemade replacement cable works, so I can understand not wanting to fix what ain't broke, but if I hit even a lick of trouble, I'd hardwire it.

[@retrozmachine1189]

@@mal2ksc Hardwiring sure fixed it for me but those cables do allow the sections of the MIII to be split for diagnostic purposes.

[@ianneill9188]

Absolutely cracking video. I loved the thought process, the theories (and their revisions), and your grounded (pun intended) logical approach to testing. That you were able to suspect and challenge initial assumptions was great to watch. Then to top it off, you have made a diagnostics ROM too. Simply stunning!

[@adriansdigitalbasement]

Thanks!!

[@tactileslut]

We're tool making monkeys. The real magic comes in sharing that tool with others and showing how it's used, both of which he's done. Think of the many hundreds of vintage devices that work could save and the dozens of previously frustrated techs that it'll help. Yay!

[@johnparker787]

you are of course joking. eeny meeny miny is not a logical approach. really really BAD. Inteligent, yes , sense.......... nope. Not a mindless rant, I've been doing this type of work for 40 yrs for a living.

[@TheRetroChannel]

Aargh that ribbon cable! Yeah it probably got worse from being put in and pulled out so who knows when it actually failed. But that logic you resurrected would have been the main fault for sure. At least we got a diag ROM out of it, and a couple of great troubleshooting videos and not just a scattergun replacement of parts

[@adriansdigitalbasement]

No parts cannon here! :-)

[@lucyfrye5365]

I wish I had seen videos like these when I was a lot younger. This sort of tinkering would have been fun. But I simply lived under the assumption that what goes on inside a pc, even the first generations, is just an inscrutable black box whose inner workings are for a select few experts only. So I focused on software only.

[@bishopofrustyiron3101]

The audio was just fine, not a worry at all! What a fascinating episode, wow, really shows the dependency of many chips on one chip or a ribbon cable. Rock on Adrian!

[@matthewkriebel7342]

Yup, audio was fine, for what it was at least.

[@mvcube]

I had the impression of an ever so slight syncronization glich. Maybe I'm overly sensible to this.

[@markkeilys]

​@@mvcube I got that too, but my setup could be shifting it just far enough out to be perceived.

[@erwindewit4073]

Wow, that was seriously hard core! Writing a diagnostic rom to fix a main board! Really cool!

[@Arachnoid_of_the_underverse]

There is a car repair channel run by Eric called south main auto channel and he always recommends testing a circuit continuity with a bulb for a load rather than just a meter because, whilst the circuit may test out as fine it requires a real loading to show if it will carry enough current for the actual circuit loading.

[@adriansdigitalbasement]

Heh yeah I watch all of his videos. And indeed, he does recommend that. It's a bit harder with a computer since it's not really designed to drive load like that ... but perhaps I can do something with a resistor and a LED.

[@garbleduser]

@@adriansdigitalbasement Try bridging across suspect lines to add more current carrying capability.

[@thirstyCactus]

EXCELLENT!!! I've heard you make the disclaimer that you are "just an amateur", but your knowledge and ability transcend the "professional" level. Amazing work, as always :)

[@a_Fax_Machine]

These videos rock. Nobody does better vintage computer repair videos

[@robf228]

Very, very cool diagnosis on the ASCII characters! (16:40)

[@adriansdigitalbasement]

Thanks!

[@m1geo]

It always fascinates me the places where you see Amateur Radio callsigns! IZ8DWF and KI3V 👌 A fascinating video, Adrian! Well done all! George, M1GEO!

[@iz8dwf]

Nice Job Adrian! I'm glad I could help!

[@adriansdigitalbasement]

You are the real expert here Frank! I'm only an imposter :-)

[@iz8dwf]

@@adriansdigitalbasement Nahh you're one of the few experts I know, believe me :)

[@mal2ksc]

Nice job! I mean repairing one computer is great, but building tools to make it relatively easy for the next guy... _that_ is the part that will have a lasting impact. Don't apologize for the bleeps and beeps either, they're part of the process, and they're probably much more annoying to you than to us, because you've heard them so many times.

[@elgrito9688]

40 minutes of mystery and horror and sincere tears of emotion at the end - I don't need Netflix anymore! :D

[@johnsonlam]

Actually the camera mic is not that bad, still clear enough to hear.

[@keninblack]

The "Eureka" moment at 41:30 is why I love working with IT and love watching your videos. Outstanding effort, well done 🙂

[@TheDurdane]

I was waiting for this one. I already from the beginning was convinced that the flat cable was involved, or at least instable. I remember that they were very vulnerable because their material was kind of non-elastic plastic and the cable could break half an inch from the connectors or get micro fractures since they had to put in a very steep angle into the PCB-connector, probably pushing too hard... This cable was not meant to take in and out frequently. Good work though! I learned a lot from you again, especially because you shared your thought process and faulty thinking, from which we learned the most. And, off course, triggering the good memories I have of my adventures with my Model III and Model 4p. The latter I still possess, since I was never able to put it out with the garbage, and now it is a very rare to find piece of history. Thanks for that, I really appreciate it! I am looking forward to your other Z80 projects.

[@robertharris2262]

I think my phone might have gone deaf. I was shouting "put the @#$%^& ribbon in upside down to see if the fault moves!" Wouldn't have affected the bit 7 problem, but should have moved the bit 3 fault to bit 4. Shows 2 separate problems, and instantly identifies the ribbon as one fault. Why? Because the only thing changed to move the error is the ribbon

[@JoelReesonmars]

Model 1and 3 were spooky like this.

[@TheDurdane]

@@robertharris2262 Brilliant idea! Actually, would'nt it move from bit 3 to 5 when turned around? Or is the first bit, bit zero?

[@LarryRobinsonintothefog]

Good things (like the diagnostic ROM) come out of trials. Your work helps others.

[@chuckterra6375]

Just a reminder, initially look for signal integrity with your scope, THEN on socketed chips, pull them and re-seat a few times to remove any oxidation on the pins and sockets, this can look like a problem that fixes itself magically, but it was the re-seating/possible pin to socket oxidation connection that was the real issue. So always scope your signals when first starting your trouble shooting. AND of course re-seat all socketed chips using de-oxit to ensure future reliability. Just a refresher comment to all... Good work Adrian, enjoy your videos... Chuck

[@jazbell7]

I knew you couldn't sleep until this was fixed.

[@wmrosju]

Your best videos are the ones where you never give up! Great work!

[@retroandgaming]

This is the proper amount of Geeky! Creating your own diag-rom with friends to diagnose this is just beyond :)

[@Vermilicious]

Good to see the problems were found. It's not trivial to find errors in a computer since you can't always rely on a program to actually run like it should. I guess the lesson learned here was that if there are bus transceivers present, you'll have to check the individual buses. It's a bit trickier.

[@magnusboman1576]

The "confused look" made me laugh out loud :D 35:25

[@nielsroetert]

Let's just create our own diagnostic ROM, so cool. Now heading to the second channel to watch more on it.

[@darkstatehk]

ADB classic fault find and repair, this is what I loved, and how I found the channel back then! So, new tee-shirt suggestion: "I put it in backwards, let's re-insert..."

[@ranieriphoto]

What a roller coaster of emotions watching this repair video! So glad you were able to find the problem Adrian. That diagnostic ROM will help many troubleshoot their machines, so your frustration was not for nothing.

[@simonlawson2236]

I said there will be a third and so glad too! It's great seeing you didn't give up and used your resources to diagnose the problem. This is what the world needs more of and not to just chuck things away. Great work as always. 👍

[@ChrisMcDonough]

That was amazing. Seems like a case of the system is always isomorphic to the organization that builds it. Somebody must have really not wanted to learn about DRAM and/or a processor!

[@binarydinosaurs]

Awesome. I think all of us who repair these things regularly go through exactly the same thought processes sometimes. Very refreshing to watch, particularly the 'IT WORKS' moment, splendid :D

[@heroinmom153]

This is gonna be a lifesaver while getting my "new" TR-80 III working!

[@allinaxford]

Glad you were able to at last repair it. The phrase cold solder joint came to mind, everything looks fine, but has really disconnected, explains the chip too, heat it enough and the connections repair.

[@Halftrip]

Watching your Commodore 64 videos got me to dig into my old C64 and fix it (it only needed a couple of chips replaced and still needs the keyboard looked at). These videos have made me want to get out my old Model I and see if I can’t figure out what is wrong with it. To know there’s now a diagnostic ROM to use makes me more hopeful.

[@T0REBK]

Thank you so much for a very entertaining video, and congratulations for finally cracking the case!

[@DavoidJohnson]

Amazing you did not give up on this again. So often you need some luck at the beginning but this demonstrates you can get there in the end.

[@cairsahrstjoseph996]

That was certainly an adventure! You should get a blue ribbon for effort (but not a ribbon cable!)

[@adamthethird4753]

Suspense, Drama, Music, Comedy. A perfect video with an excellent plot and hero's arc. I couldn't take my eyes off it. Thank you for the video!

[@tenmillionvolts]

Fantastic! Always learning. Thanks for showing us your whole journey of understanding

[@iteachtime]

That was so awesome! Thanks Adrian!

[@RoyHess666]

Thank you for helping us, help you, help us all!

[@MichaelBLive]

I love that you show so much trouble. It definitely is valuable.

[@johnmarchington3146]

Wow. That was amazing. Well done, Adrian.

[@nicksmith4507]

Nice work! Love the ups and downs along the way.

[@giovanniguaitini7454]

I really have lots of fun in watching these troubleshooting videos and you are really good at it!

[@tylerpferrari]

Extremely entertaining!!! Loved this one, Adrian

[@rogerjones8809]

Loved this video! Writing a diagnostic ROM is a great achievement. You guys make it look easy. Tools that can simplify troubleshooting speed up the process. I didn’t like that ribbon cable at all, but hey, it’s an early model home computer, and it simplified the trace design of the motherboard.

[@TheRealWulfderay]

It just goes to show what the right diagnostic tools can do! I have found myself going down similar rabbit trails many times before. When you don't know the ground truth (pun?), it can be very difficult to separate coincidence from correlation. Fantastic job getting to the root of it, and extra kudos for contributing an invaluable tool to the community!

[@mdrake42]

Great work on the Diag ROM. Great video Adrian. I learned a lot.

[@user-xx5-5885]

Awesome job! I was anticiparing you fixing this board and now the video came out! Now it's time to run something good on this machine and bring back some 80's.

[@neonbuzz7392]

These repair videos teach me so much, and remind me how little I know. Keep these amazing videos going!

[@RainerTrunk]

Thanks Adrian for your Videos. They are all Entertaining and I learn a lot from you. Greetings from Germany

[@Super_Bros.]

This channel really is one of the coolest! I really enjoy seeing you repair all these computers.

[@MrEd-qg8td]

Yeah it's working!!! Great job Adrian.

[@gabrielleeliseo6062]

That’s really cool, Adrian. Thanks for the tutorial!

[@johnas2004]

Great video, like the learning points you made about buses, and thanks very much for the TRS80 diagnostic ROM - a new tool for the box 🙂

[@noggin73]

Wow, that's a long one! Great stuff Adrian!

[@johanlaurasia]

Bravo... as usual.. you did it again. I started on Model I/III myself. Really enjoyed this video. Thanks!

[@dgrond]

Adrian thanks for your video's. It motivated me to pick up my old job as a hobby, build my own lab and have a lot off fun. Keep up the good work !!!

[@edgardovigo147]

Awesome job Adrian!

[@SonicBoone56]

Hell yeah, thanks for uploading your diagnostics program. Sure it'll help a lot of people.

[@fourthhorseman4531]

It reminds me of what they always teach us in troubleshooting networking problems. They always say, start at layer 1 and work your way up. Which would be analogous in this context to starting with the obvious physical connectivity stuff like the old janky ribbon cables. Great video, very interesting to follow you through the troubleshooting. Thanks!

[@beenieween1e]

You just confirmed a suspicion of mine- I do commercial low voltage and I've had CAT5 lines that tested fine on a certifier or the basic Ethernet tester, but wouldn't pass a signal- and a new cable run fixes the issue. I thought continuity meant continuity, and was confused when swapping the cable fixed the issue. Every two-video series for a bad ribbon cable is a learning experience! :D

[@timothyp8947]

Have loved this series, although I daresay you not so much! It really shows the value of having the test ROM - with that you were able to home in on the elusive problem. Did half wonder if the ribbon testing OK might’ve implied what it was plugged into was sick - and your new, sturdier cable made better contact. The bus transceiver coming back to life is just plain weird.

[@TheBioWanderer151]

So Ahab found his White whale, and lived to tell the tale. Good job man, this was a pretty great series and am glad it finally works for ya.

[@hugoegon8148]

Your patience is amazing! 👍🏻 Audio was good.

[@Zone1242]

Well done - persistence pays off in the end!!

[@DavidKehley]

Woo just got home and saw Adrian had a new episode good way to end my day

[@diskettenfett3161]

Great video! I really like deep in-depth troubleshooting and fault analysis. Keep up the good work :)

[@kernelramdisk3348]

Hello Adrian, I just started watching your videos like a month ago or so and I like them a lot. This particular video was awesome, the fact you were able to figure out those bits were flipped by looking at the ascii table and using that information to troubleshoot the problem really blew my mind. Thank you very much for your awesome content, now I don't miss any of your videos on Saturday!

[@Walczyk]

That audio was really really good!!! Impressed with the post work

[@xpepos]

Very good detective work. I have TRS in my eyes!

[@michaelelsy2209]

I always find your videos entertaing and informative even though I know nothing about computers.

[@DKbananas]

Great video Adrian. Your positive energy in the troubleshooting and discovery of a problem is what makes your videos stand out. Some long time you tubers start to fade in their creativity and excitement, and it shows in the videos.

[@bernardoeylenstein1643]

That was a really thrilling video! Too many things happened in both parts of the fixing, very clever assumptions. Interesting!

[@kjtroj]

Another system comes alive! Good to see another diagnostic tool become available.

[@CommodoreGreg]

I really like the approach used in your custom diag rom.

[@ddjazz]

What a thriller episode , the Eureka and fail moments just made this so fun to watch , thx for sharing all of it , the audio was good enough to enjoy it.

[@MikesArcadeMonitorRepair]

Fascinating. Great job Sir!

[@alexandermaasland3494]

Well done again Adrian, you finally have that nasty bug squashed. What a relieve that must be :) Good job!

[@DavidLatham-productiondave]

Congratulations. You looked so relieved when you figured it out. Nice one. The endorphin hit looked so real for you.

[@andrewquinn4081]

My favourite part of your videos is your reaction when you figure the issue out… keep up the great work!

[@yakattack1069]

Love the "long" videos! Keep them coming!

[@stefanweilhartner4415]

great repair series!

[@pauldourish]

Tremendous! Enjoyed this one so much!

[@thevortexATM]

i had one of the TRS-80 color computers as my first system, this brings back so many memories, i am so glad you got it working, awesome series with a great ending!

[@timbald]

Adrian, well done. It's been a brilliant mini series. Really good that you don't cut out in post your mistakes. Somehow your humanity in it all makes it really work.

[@terryuland6502]

This video series was very interesting to watch and reminded me of all the times I've chased my tail in the world of both computers and automotive mechanics, only to find out the main problem was a part that would have taken a few minutes to replace (a flaky cat5 cable or old vacuum hose for example). So now I've learned to replace anything that's both suspect and cheap & easy to replace without even bothering with testing. That being said the tail chasing makes for great content and helps teach others how to troubleshoot.

[@joshuastanden]

I love watching these troubleshooting videos.

[@stuartbrownlee3108]

Awesome! I didn't want you to be defeated by this motherboard problem and am glad to have seen its solution.

[@foobar-9k]

These 47 minutes went so fast! LOL! Really enjoyed the video! Greetings from Argentina!

[@root42]

Always follow up a continuity check with an Ohms check. :) Good fixing and troubleshooting!!

[@teekay_1]

Nice work Adrian. Mistakes are how we learn.

[@el-chapo8094]

🙌 keep up the good work Sir.

[@rolandknoll6567]

Hi Adrian, with the bus transiver can be that on the pin of the Databus 7 was a so-called cold solder joint. Since you soldered out the IC and then soldered in the socket, the cold solder joint has disappeared or repaired. I suspect that was the error.

[@paveljelinek772]

0:40 can't wait to sea how it'll go. I've been praying for yoo Adrian to see this finally fixed

[@Plarndude]

Whew! Glad you figured it out!

[@RetroClaire]

Really enjoy videos like this Adrian. Great work on the test ROM too. Early days but the kind of thing that really benefits the fixing community. Little wonder you struggled with this one 👍🕹️