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)
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 :)
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!
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!
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
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.
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 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.
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
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.
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
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.
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.
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.
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..."
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
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
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. 👍
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 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.
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.
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!
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.
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!
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!
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.
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.
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.
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!
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.
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.
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.
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!
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.
I am sooo Happy for you Adrian, such a sweet repair! Big shout out to iz8dwf (Frank) and David for helping with the debug ROM, excellent work you guys, great video.
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, as always! Thats why after testing CPU, other data and adress buss tests needed to be done, especially, if there is buffers and multiplexors.. 😉
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!
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.
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.”
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.
i love your videos, you truly are an expert, Uncle Doug knows AMPS, Mr. Carlson knows Radios (and everything) ,. U know (and David Murry ) these computers,.,, I learn as much or more about electronics than I would @ UNI you guys are great teachers !!! frfr
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!
I recently found this channel, because my retro wave kicked be back to the beginning of the eighties. This video is more thrilling than any detectvie story I've watched. Especially the ASCII binary reveal part is nerdy to the max and I thank you for that. I'm thinking I'l break my leg so I can lay down for a few weeks without being disturbed! :) Subscribed and liked, great channel!
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.
Found your channel a month back and im slowly working my way thru your back videos. @Vidfavne is correct. your content is more entertaining then anything on TV/Cable. Wish i was around for the trs 80. i made my start on a ZX Spectum. always found coding is basic back in the day relaxing. Keep up with the amazing videos. And thank you for the very interesting content. Dave
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 UA-cam 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)
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 :)
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.
Good things (like the diagnostic ROM) come out of trials. Your work helps others.
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.
Wow, that was seriously hard core! Writing a diagnostic rom to fix a main board! Really cool!
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!
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!
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.
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! :-)
The "Eureka" moment at 41:30 is why I love working with IT and love watching your videos. Outstanding effort, well done 🙂
These videos rock. Nobody does better vintage computer repair videos
It always fascinates me the places where you see Amateur Radio callsigns! IZ8DWF and KI3V 👌
A fascinating video, Adrian! Well done all!
George, M1GEO!
Your best videos are the ones where you never give up! Great work!
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 :)
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.
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?
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.
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.
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.
Very, very cool diagnosis on the ASCII characters! (16:40)
Thanks!
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.
Great video Adrian. I totally enjoyed the process! (And good to see I’m not the only one forgetting to plug in the mike!)
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..."
This is the proper amount of Geeky! Creating your own diag-rom with friends to diagnose this is just beyond :)
My favourite part of your videos is your reaction when you figure the issue out… keep up the great work!
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 🙂
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
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
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. 👍
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.
40 minutes of mystery and horror and sincere tears of emotion at the end - I don't need Netflix anymore! :D
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.
Thank you for helping us, help you, help us all!
Let's just create our own diagnostic ROM, so cool. Now heading to the second channel to watch more on it.
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.
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!
I always find your videos entertaing and informative even though I know nothing about computers.
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.
I love that you show so much trouble. It definitely is valuable.
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!
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!
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.
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.
Wow. That was amazing. Well done, Adrian.
This channel really is one of the coolest! I really enjoy seeing you repair all these computers.
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.
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!
Always follow up a continuity check with an Ohms check. :) Good fixing and troubleshooting!!
Awesome! I didn't want you to be defeated by this motherboard problem and am glad to have seen its solution.
Another system comes alive! Good to see another diagnostic tool become available.
Congratulations. You looked so relieved when you figured it out. Nice one. The endorphin hit looked so real for you.
I knew you couldn't sleep until this was fixed.
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.
Great video! I really like deep in-depth troubleshooting and fault analysis. Keep up the good work :)
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.
These repair videos teach me so much, and remind me how little I know. Keep these amazing videos going!
Yeah it's working!!! Great job Adrian.
Thanks Adrian for your Videos.
They are all Entertaining and I learn a lot from you.
Greetings from Germany
Nice work! Love the ups and downs along the way.
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.
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!
I love these long, rambling videos trouble shooting issues.
Awesome! Hindsight is 20/20... Always check your data bus, esp. After the buffers..
Extremely entertaining!!! Loved this one, Adrian
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.
I really have lots of fun in watching these troubleshooting videos and you are really good at it!
I am sooo Happy for you Adrian, such a sweet repair! Big shout out to iz8dwf (Frank) and David for helping with the debug ROM, excellent work you guys, great video.
Woo just got home and saw Adrian had a new episode good way to end my day
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, as always!
Thats why after testing CPU, other data and adress buss tests needed to be done, especially, if there is buffers and multiplexors.. 😉
Well done - persistence pays off in the end!!
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!
I really like the approach used in your custom diag rom.
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.
Your patience is amazing! 👍🏻 Audio was good.
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.”
Great work on the Diag ROM. Great video Adrian. I learned a lot.
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 !!!
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.
Thank you so much for a very entertaining video, and congratulations for finally cracking the case!
Bravo... as usual.. you did it again. I started on Model I/III myself. Really enjoyed this video. Thanks!
Very good detective work. I have TRS in my eyes!
Fantastic! Always learning. Thanks for showing us your whole journey of understanding
Hell yeah, thanks for uploading your diagnostics program. Sure it'll help a lot of people.
That’s really cool, Adrian.
Thanks for the tutorial!
Actually the camera mic is not that bad, still clear enough to hear.
i love your videos, you truly are an expert, Uncle Doug knows AMPS, Mr. Carlson knows Radios (and everything) ,. U know (and David Murry ) these computers,.,, I learn as much or more about electronics than I would @ UNI you guys are great teachers !!! frfr
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!
That was so awesome! Thanks Adrian!
These 47 minutes went so fast! LOL! Really enjoyed the video! Greetings from Argentina!
I love watching these troubleshooting videos.
Whew! Glad you figured it out!
I recently found this channel, because my retro wave kicked be back to the beginning of the eighties. This video is more thrilling than any detectvie story I've watched. Especially the ASCII binary reveal part is nerdy to the max and I thank you for that. I'm thinking I'l break my leg so I can lay down for a few weeks without being disturbed! :) Subscribed and liked, great channel!
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 audio wasn’t bad at all, you did an excellent job in post.
That was a really thrilling video! Too many things happened in both parts of the fixing, very clever assumptions. Interesting!
Found your channel a month back and im slowly working my way thru your back videos. @Vidfavne is correct. your content is more entertaining then anything on TV/Cable. Wish i was around for the trs 80. i made my start on a ZX Spectum. always found coding is basic back in the day relaxing. Keep up with the amazing videos. And thank you for the very interesting content. Dave