Using our new diagnostic ROM to fix a TRS-80 Model III!
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- Опубликовано: 6 сен 2024
- #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/mis...
2364 adapter PCB:
www.pcbway.com...
Frank IZ8DWF's channel: (for really amazing repairs)
/ iz8dwf
When good caps go bad: (t-shirt donated by Jesse)
www.teepublic....
Adrian's Digital Basement Merch store:
my-store-c82bd...
Adrian's Digital Basement ][ (Second Channel)
/ @adriansdigitalbasement2
Support the channel on Patreon:
/ adriansdigitalbasement
-- Tools
Deoxit D5:
amzn.to/2VvOKy1
store.caig.com/...
O-Ring Pick Set: (I use these to lift chips off boards)
amzn.to/3a9x54J
Elenco Electronics LP-560 Logic Probe:
amzn.to/2VrT5lW
Hakko FR301 Desoldering Iron:
amzn.to/2ye6xC0
Rigol DS1054Z Four Channel Oscilloscope:
www.rigolna.co...
Head Worn Magnifying Goggles / Dual Lens Flip-In Head Magnifier:
amzn.to/3adRbuy
TL866II Plus Chip Tester and EPROM programmer: (The MiniPro)
amzn.to/2wG4tlP
www.aliexpress...
TS100 Soldering Iron:
amzn.to/2K36dJ5
www.ebay.com/i...
EEVBlog 121GW Multimeter:
www.eevblog.co...
DSLogic Basic Logic Analyzer:
amzn.to/2RDSDQw
www.ebay.com/i...
Magnetic Screw Holder:
amzn.to/3b8LOhG
www.harborfrei...
Universal ZIP sockets: (clones, used on my ZIF-64 test machine)
www.ebay.com/i...
RetroTink 2X Upconverter: (to hook up something like a C64 to HDMI)
www.retrotink.com/
Plato (Clone) Side Cutters: (order five)
www.ebay.com/i...
Heat Sinks:
www.aliexpress...
Little squeezy bottles: (available elsewhere too)
amzn.to/3b8LOOI
--- Links
My GitHub repository:
github.com/mis...
Commodore Computer Club / Vancouver, WA - Portland, OR - PDX Commodore Users Group
www.commodorec...
--- Instructional videos
My video on damage-free chip removal:
• How to remove chips wi...
--- Music
Intro music and other tracks by:
Nathan Divino
@itsnathandivino
This was more entertaining than anything I can currently find on Netflix, Amazon Prime, Viaplay or Disney+
Bro, this was better than those south american soap operas that my grand mother used to watch XD
Stranger things was pretty good.
And yet we still don’t pay for RUclips premium
Maybe it's the vodka!
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.
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)
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!
Thanks!!
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!
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.
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!
Yup, audio was fine, for what it was at least.
I had the impression of an ever so slight syncronization glich. Maybe I'm overly sensible to this.
@@mvcube I got that too, but my setup could be shifting it just far enough out to be perceived.
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.
I modded my long gone MIII to the extreme with all sorts of homebrew including an 8MHz Z80H, overclocked of course.
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.
@@mal2ksc Hardwiring sure fixed it for me but those cables do allow the sections of the MIII to be split for diagnostic purposes.
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.
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
Replace them with kapton flex cables or an actual ribbon cable. This 70s paper crap goes in the garbage.
might pass dc current, but a high frequency square wave with no crosstalk: Some of the time
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.
Signal Generator @ 2 MHz and oscilloscope, how does the ribbon mangle the communication?
We want a follow up!
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
No parts cannon here! :-)
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.
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.
@@adriansdigitalbasement Try bridging across suspect lines to add more current carrying capability.
It always fascinates me the places where you see Amateur Radio callsigns! IZ8DWF and KI3V 👌
A fascinating video, Adrian! Well done all!
George, M1GEO!
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 :)
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.
Wow, that was seriously hard core! Writing a diagnostic rom to fix a main board! Really cool!
These videos rock. Nobody does better vintage computer repair videos
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.
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
Model 1and 3 were spooky like this.
@@robertharris2262 Brilliant idea! Actually, would'nt it move from bit 3 to 5 when turned around? Or is the first bit, bit zero?
Nice Job Adrian! I'm glad I could help!
You are the real expert here Frank! I'm only an imposter :-)
@@adriansdigitalbasement Nahh you're one of the few experts I know, believe me :)
The "Eureka" moment at 41:30 is why I love working with IT and love watching your videos. Outstanding effort, well done 🙂
Very, very cool diagnosis on the ASCII characters! (16:40)
Thanks!
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.
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.
This is the proper amount of Geeky! Creating your own diag-rom with friends to diagnose this is just beyond :)
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!
Your best videos are the ones where you never give up! Great work!
Good things (like the diagnostic ROM) come out of trials. Your work helps others.
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.
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. 👍
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
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.
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
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..."
40 minutes of mystery and horror and sincere tears of emotion at the end - I don't need Netflix anymore! :D
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.
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!
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.
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!
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.
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.
Let's just create our own diagnostic ROM, so cool. Now heading to the second channel to watch more on it.
Actually the camera mic is not that bad, still clear enough to hear.
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!
The moment the actual computer booted up with the diagnostic ROM (and displayed the lines with the repeating pattern) I was looking at bit patterns to figure out which were stuck high/low - even before you made it there. ... And the only reason I knew to look for that was because of your earlier videos. You, Sir, are as education as you are inspirational, and the folks who watch your videos always come away better for the experience. Thank you.
Great video, Adrian, and congratulations on successfully repairing it! You learned a lot along the way, too, always good.
A few suggestions / comments:
(1) Don't forget to look for poor or cold solder connections on things like the IC pins. I've seen weird results, and that buffer chip (8T26?) might have been something like that.
(2) Broken circuit traces. Don't assume the signals actually go everywhere they're supposed to be. I've seen a trace under an IC cut by one of the pins being bent under, with that pin itself working fine soldered to its pad. (That was in a new board manufacturing test environment, admittedly.)
(3) Last but not least, when tracking down signals stuck high or low, I used to desolder just the signal pins affected on each of the chips and try to isolate them from their pad or plated through hole. That way I could try to determine where the fault occurred, which chip caused the fault without fully removing the chips. Obviously that doesn't always work and you can't isolate the pin, but it's something to keep in mind.
Again, great video. And I had no issues with the audio you were worried about. 🙂
Glad I found your comment. The bus transceiver chip may indeed be flaky, but since it has gone from hot to cold a zillion times, it could have invisibly wedged itself a cold joint in the PCB.
Re-soldering the pins may have been the real fix.
@@GnuReligion Glad to have passed along a tip or two.
One more related to isolating an IC pin. An open TTL logic input will not be high or low (+5V/0V) but typically something around 1.4~1.7 if I recall. Meanwhile an isolated CMOS logic input can look like a zero volt low on a scope yet not be. I would sometimes take a 100k resistor on a "Porter pick" back to the +5v power so I could provide a low-current input, then switch it to ground to tie it low. I caught a few cases of bad CMOS inputs that way. That was on the old 4000-series CMOS logic chips, trying to recall how the high speed CMOS TTL-equivalents ("74HCTxxxx") acted.
@@bobblum5973 What would REALLY be OCD, is to take the output of a trimmer, feed it though a trusted opamp, and roll the voltage to extents, and record exactly where the new Chinese logic chip flips HL, and LH, and where its output is at high and low. Ok, I do this. Been burned too many times. Modern CMOS makes life easy compared to the days of NMOS and open collector.
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
Great video Adrian. I totally enjoyed the process! (And good to see I’m not the only one forgetting to plug in the mike!)
This channel really is one of the coolest! I really enjoy seeing you repair all these computers.
Thank you for helping us, help you, help us all!
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.
The "confused look" made me laugh out loud :D 35:25
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.
I knew you couldn't sleep until this was fixed.
This is gonna be a lifesaver while getting my "new" TR-80 III working!
That was certainly an adventure! You should get a blue ribbon for effort (but not a ribbon cable!)
Great video! I really like deep in-depth troubleshooting and fault analysis. Keep up the good work :)
My favourite part of your videos is your reaction when you figure the issue out… keep up the great work!
These repair videos teach me so much, and remind me how little I know. Keep these amazing videos going!
Great video, as always!
Thats why after testing CPU, other data and adress buss tests needed to be done, especially, if there is buffers and multiplexors.. 😉
I hope people will understand how difficult it is to chase down problems and fix these machines. Well done - appreciate the realism of steps and missteps!
If at first you don't succeed, Try, try again. Now you have a diagnostic ROM to help speed up the next TRS-80 repair! Great work, Adrian. I always love to watch your videos and this one was particularly good, just because it had you stumped. But you didn't give up.
Always follow up a continuity check with an Ohms check. :) Good fixing and troubleshooting!!
Another good video, Adrian,
Many moons ago, I wrote a similar diagnostic test program for the Sinclair Spectrum to test video and system RAM.
It also Wrote and Read hex AA and 55 plus a walking 1 Bit pattern for testing all the RAM.
I had a Floppy drive interface for the Spectrum that I used to run the test and it ran as soon as I started the machine.
I found out the Spectrum RAM was famous for going faulty. If I remember right some RAM on the Spectrum was half bad to start with.
Well done getting this machine running again.
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.
Well done - persistence pays off in the end!!
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 🙂
I always find your videos entertaing and informative even though I know nothing about computers.
This is why its best to always check simple to replace items first, although with the ribbon testing good for continuity I can definitely understand why you didn't replace it right away. I wonder if maybe the ribbon actually has an out of spec, or marginally in spec, pin diameter for the bit 3 connection at one end and the age of the socket it is connected to is just worn from many removals and replacements of the cable.
Excellent video and great job on getting a diagnostic ROM for the model III made so quickly. Love your videos.
Hi Adrian: been watching your channel for a while. I owned a model III and it developed a video issue, I don't recall what the symptoms were, but I found that those video cables CAN be dodgy and think that your bodge solution may actually be a good permanent fix just solder them on the bottom of the board to the pads :-) But those data bus cables are the first thing i replace before troubleshooting those old TRS-80s. I have fixed the 4 or so I have owned. My last model III was sold to a local collector in perfect working order with normal wear type cosmetic issues. To my knowledge still works now and it was sold over 6 years ago.
My solution was to solder ribbon cable on the back of the PCB. For the strips that went to the FDC and RS232 card, I replaced the PCB headers so I could use normal IDC type connectors and ribbon wire. Tandy really made a poor choice with the use of that flex cable stuff. Every single MI / MIII that I have had my hands on has suffered from it coming apart and even poor connections where the pins were crimped onto the flex itself.
I love that you show so much trouble. It definitely is valuable.
Awesome! I didn't want you to be defeated by this motherboard problem and am glad to have seen its solution.
I really have lots of fun in watching these troubleshooting videos and you are really good at it!
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 👍🕹️
I really like these longer videos. I normally have attention problems, and it's actually able to hold my attention. Even on TRS-80 stuff, I was always a Commodore user, I find it totally watchable. Keep up the good work.
Haha, I already wrote about the problem with the bus conflicts in my comment in the previous video, and suggested a procedure for that. I am very glad to see that you finally got it working ! Keep up the good work Adrian! 👍
This is my comment from the previous video: “The chip that is trying to pull the line down seems to fight against another component holding the line up the whole time. There may be another broken chip whose select(&deselect) lines are not working properly allowing it to drive the line high the whole time… make a list of all chips directly connected to the bus (or the line you were measuring) and try checking their select state. If a chip is trying to write to the bus all others should be silent.”
Moisture ingress into old silicon chips can exhibit the bad-->good symptoms you have experienced. In your part one video, many of the high with 'glitch' partially low on those 138 devices is quite normal as address changes settle at the outputs.
Well done Sir. We all learn by failing. Good luck with final re-assembly.
If enough interest, I reckon you might enhance your diagnostic ROM with larger memory and on-card address manipulation to cover the various options with mini-shunts or whatever.
I’m still learning microelectronics, but I have nearly 20 years of experience in automotive electronics. In the automotive world, resistance testing of circuits is basically never done, and this is why. A circuit can be connected by a single strand of wire and pass a resistance/continuity test, but fail to transfer any usable current. Obviously you had an additional issue with the other bit being stuck low, but the issue with the ribbon cable would have been found by testing the ribbon cable under a load (voltage drop testing) rather than continuity testing. Not trying to be critical or tough on you, but it’s a learning experience. Continuity tests don’t tell you if a circuit is good, they *only* tell if a circuit is bad.
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.
As others have said, I don't know why, but this video was absolutely fascinating for me. I was just glued to everything said/shown. Will for sure watch the companion vid. Great work by everyone who collaborated on the diag rom.
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.
I don't know anything but I was shouting "change that janky ribbon cable" at my tv for two episodes, glad to see my brain has a good idea at least every once in a while
0:40 can't wait to sea how it'll go. I've been praying for yoo Adrian to see this finally fixed
Another system comes alive! Good to see another diagnostic tool become available.
Awesome work - great to see the design process for the diagnostic ROM! One way to support testing machines with different amounts of DRAM would be to test each section of RAM separately, so if you know your computer has only say 16kB of RAM, you can expect the tests of higher sections to fail. Could say "failed or not present" to avoid confusing the user if they aren't familiar with this. Have as many section tests as there are DRAM configurations.
That’s really cool, Adrian.
Thanks for the tutorial!
Awesome! Hindsight is 20/20... Always check your data bus, esp. After the buffers..
Wow. That was amazing. Well done, Adrian.
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.
For your diagnostic, just auto configure the memory test. If the test reports less ram then you have installed, that in and of itself is important information. It's easy to test at say a 1K boundary address, to see if ram is there.
By the end of the second video, I knew the ribbon cable was the problem. The squirreliness of the machine everytime it was rebooted is what convinced me. You tested for continuity, but that sketchy, delaminating cable was carrying rapidly changing data signals, not straight DC.
BTW, I'm addicted to your videos. So nice to see old school component level repairs. Did you ever test that second cheap o-scope? I couldn't find the follow-up video if you did.
Nice work! Love the ups and downs along the way.
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!
Glad to see this series. My Model III has been in storage for many years, but I’ve been thinking about getting it out to see if it’s alive. Bought it “new,” freight damaged, shattered CRT, in 1984. Installed an amber CRT, upgraded RAM to 48K, wrote some BASIC programs for my wife to use for work. Later added four floppy drives, then an 8 meg hard drive and the hi-res graphics board. Still have the machine with two floppies, graphics, dot matrix and daisywheel, and best of all, the 300 and 1200 baud modems! I wonder whether the drawers of software on floppy are still readable.
So I did get my Model III out of storage. It refused to boot, filling the screen with a single character...different on each reset, but always one character repeated. Turns out it was the CPU gone bad. I swapped a Z80A chip into the machine and it’s fixed.
Congratulations. You looked so relieved when you figured it out. Nice one. The endorphin hit looked so real for you.
I really like the approach used in your custom diag rom.
Awesome video! These repairs where you end up going down multiple paths and even make a few mistakes are incredibly valuable. Seeing the thought process and learning where to concentrate efforts for future reference is very educational and I really appreciate how you share and explain everything.
I'm going to have to grab that diagnostic ROM. I have a Model I I need to work on that just pops up with garbage on the screen. Tho it's been weird - when I first tried it out, I could hit reset and the garbage would change. After a few attempts it it started filling the screen from bottom to top with "A"s, and after a couple more tries it's now just garbage with no effect from reset. I'm sure this diag will be a big help! Thanks so much for you and the other guys creating it!
Doing this the way you did showed a lot of problems not everybody's going to have a lot of the testing equipment you've got but you went through a lot of diagnostics showing people different things and how they work and how to approach them to fix them. I would rather see you guys. You content creators that do this kind of repair. Go through a longer process and show how things like this and how problems like this can come about then have easy fixes didn't have the resources on the internet that we have today
Whew! Glad you figured it out!
At least two separate faults. This is kind of situation that eats repair time!. You just have to work the problems one by one and eventually the fault disappears in a puff of logic lol. That was a lot of effort most workshops would have given up due to cost. So very well done for pushing on. And you ended up with a diag rom - very good.
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!
Woo just got home and saw Adrian had a new episode good way to end my day
Well the good thing is that you got the diagnostic rom out of it all
The audio wasn’t bad at all, you did an excellent job in post.
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 !!!