Great to see the beeb getting some love. Maybe not the ultimate, but certainly very close to an ARM1 :) Interesting that they didn't go for the TUBE, but for faster disc access, it makes sense.
Yellow diode is a zener, 3.9v, an essential part of the voltage regulation circuit. A regular small signal diode like 1n4148 there will cause dangerous overvoltage. Put the correct component like 1n4730 or 1n5915 there and it should work. Cheers!
Thanks for that I was reading of the schematic which I struggled to find and could only find a 1n listed around the battery area I’ll get this removed and order the other. Thankyou so much for your comment and help
It’s amazing how many of these where around and used in different machines I’m learning more and more. The QL has the same cpu as well and I think the early Atari st although I could be wrong. Thanks for your comment
Yep I was about 14 and programming my Sinclair Spectrum in Z80 machine code and had a friend in the software industry telling me details about the 68000 and the Amiga. Everything just sounded amazing - so many registers!
@andrewdunbar828 yeah it was a huge leap from the 8bit era. I remember seeing and hearing the Amiga for first time and was dumbstruck lol 😂. Seems we don’t have that leap anymore :) thanks again for your comment.
Very interesting looking board. I hope you get it working. Try taking the bigger chips out and retesting the voltage. I think it's more likely to be one of them than a dead short (the resistance is too high for a short anyway). You can also check the resistance of those arrays by probing from the common pin to each of the others.
Indeed, tantalum bead capacitors do fail short circuit, they don't fail to 35 Ω. It may be worth briefly removing the two tantalums to confirm that they are OK with your little tester, then they can go straight back in. Do you, @retro4u, know which ones are the tantalum bead capacitors?
@@Penfold42thankyou will remove these and give them a look. Thanks for your comment these have been mentioned a few times so so certainly worth a look :) 😊
I’m sure it will be working soon. The battery 🪫 damage wasn’t so bad so I’m sure we have hoops and I’ve had lots of tips and hints of people on here. Thanks for the comment.
without having a circuit diagram its hard say if 35 omhs is low, but since you are not getting 5 volts (I assume) that clearly implies something is gone (technically 35 omhs isn't a short) you should remove all the socketed chips and see if your 5 volt line returns... you tend to get low resistivity from/near power supply circuits (analog circuits)... so provided the board was disconnected from its PSU while measuring, the omh reading does seem low for a digital board, that said, there does seem to be analog circuity in lower left quadrant of this board, but your thermal imaging doesn't show much heat coming from this area... touch tests might be better than your thermals as no digital IC from this era should be so hot that can touch them for at least couple second... if you can touch for a split second that implies a bad chip.
Wow thanks so much for such a detailed explanation. I will of course try pull all the chips I did think that pull the socketed ones. That will be a job for next week for sure. There is a circuit diagram out there but it’s hand drawn and I struggled to read some of it plus I’m still not 100% on reading it. I found the cap ect by tracing from the battery. Thanks again for your comment and help it’s gratefully appreciated 😊
IBM had only OS/2. This thing has OS9! It has to be over 4 times better! 68008 CPU is a weird beast. It runs 32 bit code on 16 bit internal architecture with 8 bit external bus. Someone should interface it with QSPI (4 bit) memory.
I emulated this board in MAME a few years ago, so know what to expect when you get it working. I've never seen a real board running, only my emulation, and doubt anyone else has either in likely over 20 years! A surprising amount of documentation exists for this board, including schematics, which I presume you've found? So your board didn't come with the ROM, presume you have the OS9 floppies or have you downloaded those too?
@@ngbarnes I have a full set of disks originals and backups :). Yeah I found the schematics just and the installations guide. I’m looking forward to getting it work of course but only a matter of time I think 🤔 these things are sent to test us :) So cool that you emulated this. I have no idea what to expect lol 😂 thanks for the comment
@@Retro4u whilst there are images of the disks out there I'd appreciate seeing your originals imaged too, with photos, for comparison as it's not obvious which are original and which have been modified. Just want to have a clean set of originals imaged.
You can try a Motorola 68HC001. It's a PLCC 68000 on which you can select 8 bit and 16 bit mode with a hardware pin. This would allow to run an Amiga 600 with 8 bit.
@Michael.Werker How would that work exactly? Are you suggesting a whole new PCB with the appropriate PLCC-68 socket and the inevitably slightly different support circuitry? Or maybe an adapter board that adapts the PLCC-68 to the DIP-40? If that is the case, then there'd only be an 8-bit bus so the 16-bit capability of the 68HC001 would be unavailable.
You can't run an Amiga 600 with a 68hc001 running in 8 bit. The rest of the computer relies on 16 bits, you wouldn't be able to get the chipset to do much if you can't write to upper 8 bits of it's registers
@@Brian_Of_Melbournethe mc68sec000 can also run in 8 bit mode. I assume the suggestion was if you needed to replace the 68008 or build a new board. Though running in 8 bit mode is a terrible idea. It basically halves the performance. Fitting 16 bit ram and ROM is a better option
@Brian_Of_Melbourne If Pin 8 of the 68HC001 is GND, then the processor is in 8 bit mode after reset. I also tried to find a suitable PLCC/DIP-Adapter, but wasn't successful. @phil6859 I know that an Amiga won't work in 8 bit mode, but it should result in some interesting crashes :-D
The capacitor you finished soldering at 10m, I could not fully tell but it looked as though both sides were soldered to the same track or one track was close to the other.
When you power it up, at around 21:15, your PSU shows 5.05 Volts, but when you measure this on the PCB, right where the PSU is connected, then you get 3.5 Volts. So a volt and a half has vanished IN THE WIRES FROM THE PSU. Let's do the calculation (Ohm's Law). R = V / I. 1.5 V / 0.7 A = ~2.1 Ω. That's too high for connecting leads, by two or three orders of magnitude. Measure them, individually, with your (soon come) milli Ohm meter. My bet is that one lead will be passable and the other will be contributing most of the 2.1 Ω. They'll be unreliable crimps that need to be properly soldered.
@@Retro4u Start with the common lead on your DMM (set to the 20 Volt range) fixed soundly on the negative terminal of your PSU. Then you can measure the voltages at the PCB (nominally 0 Volts and +5 Volts) to see where you're at. It may be helpful at this point to make a lead with a decent crocodile clip on one end and a 4 mm banana plug on the other for activities like this. Further testing you can do to look at the power draw across the PCB is the set your DMM on 2 Volts, connect the common lead to where the 0 Volt connection is on the PCB. Then probe around on the various 0 Volt points on the PCB (like the 'ground' pins on various chips, etc). You may find some points are higher than others, these are points where the current flowing in the PCB tracks and the resistance of those tracks is leading to a voltage drop. You can do the same with the +5 Volt trace(s).
Power rail is obviously shorted , I would start check the two tantalum caps , 2 orange blobs between the big chips and also down by the plug / cutout square, they are notorious for failing and blow up itself or power supply. Bit concerned with 2 chips getting so toasty but that might be normal, also the resistor pack getting so hot dont seem normal but its obviously not the resistors fault , it would be something shorted if that is not normal, not sure what they do, might also be normal. I would start desolder both tantalums and see if that changes the reading from 36 ohms, and also I sure hope you replaced the diodes with the proper ZENERdiode voltages and not just normal diodes
Yeah I’ve order the diodes. Some people are saying they are short some not. Yeah 👍 I plan to remove the tantalum caps and test them seeing it sorts it out. Yeah I thought that about the resistor array I will check that out with readings later as well. :) thank you so much for the suggestions and detailed help it’s much appreciated and thanks for the comment t
@@Retro4u zeners are finicky. I heard moisture can cause them change value making them look fine but give wrong voltage so checking all voltages is always a good idea.Also they are a common failure. repairing amplifiers I already had to replace a handful of them. running a 4148 diode instead of a zener will forcefeed something 5v that wants 3.9volts making whatever that is very unhappy, I could not read the red markings but the yellow diode was a 3.9v zenerIts important to always use the right kind of diode , some places need a germanium diode and wont work right with a silicon one with different forward voltage.. Rifas is another common fail , they split , soak in water from air and go kaboom .amazing amount of smoke just one tiny rifa can make, one from old scope blacked out my whole second floor, it seemed to run fine for a minute and then full pompei..... Probably good idea replacfe any rifa with polyprop x or y cap and any tantalums with perhaps ceramic ones, they are much lower esr resistance , in some cases that matters but I doubt it matter here. I had an old pc mainboard totally short out a rail with over a dozen tantalums, removed them one by one to test out of circuit, even with milliohm meter u might not see if the one next door or the one measured is bad, rails are supposed to be low impedance. Often rifas look fine until being on a a few mins. (evil buggers) and best is they always hide deep inside power supplies where u cant see them until they go, can have hidden cracks on underside etc old rifas is always a bad thing.
@kristiansolstad9068 yeah experienced many rifas and magic smokes with the apples and bbc power supplies. After what you said I’ll probably just replace those caps to be certain there is only a few of them. Just need to find out what rating they of the schematic :) thanks again for such a detailed explanation and help :)
@@Retro4u the x2 / y or whatever is probably best bet in mains filters, one fail short the other fail open and theyre safety caps. any mains filter cap wont matter if open or missing , just a bit more theoretic noise. value should be on then tho I have seen them with sides missing etc ;) Sometimes diagnose is easy I saw a couple circuits boards with giant holes with one half leg remain , one was a big motor device the other high voltage part of a tv , the 3 inch gaping hole gave me a small clue to start diagnose ;) got the tv for free coz it was "blown up with fire and obvious could not be repaired" then again a 50 cent 1250v discarded cap from my junk pile (was given to me for being "unsafe" / recalled) made it work for decades more, until someone stole it. always fun when you have to guess where tracks was supposed to have been .... semiconductors can be hard to diagnose, sometimes they split in half other times look fine and are bad and you cant find out until running them in a circuit with load. zeners f.ex wont give the right voltage if current is way off. The really fun ones are intermittent so every test they measure and perform perfect and then randomly fail. Parts can also look like crap and work fine... Ceramic / polyprop / plastic caps seem to work forever or until someone break them in half.
@kristiansolstad9068 yeah tbh I lot of the ceramic caps I replaced where either damaged or I loved them and they snapped lol 😂. I’m sure with all this info I’ll be able to get this board up and running again. I just need to source these caps of the drawing ✍️ I find it hard to follow lol but managed to find the diode and it was 3v9 so ordered one. I’m still learning this stuff and you have been a great help. :) table yet again
For reference a short to ground is very unlikely to be a ceramic cap, when they fail open circuit, effectively just removing the cap from the circuit. Tantalum caps on the other hand fail closed and create a short. Electrolytic caps tend to fail open circuit. You do have a tantalum cap in the middle lower section, right next to the "cut out" Do I need to point out that the TRS80 image you used is not a COCO, it isn't even a TRS80... The CoCo computers look relatively similar to the Dragon in either black/silver or cream cases
@@julianbrown1331 hi 👋 thanks for the comment in the next video I removed the tants and found 1 faulty one. Tbh Ive never even seen a coco and that pic a was a from a site talking about them so they must be wrong as well but good spot. Dragons I saw as a child. I’m still working on it but getting closer thanks for your help and comment
That second diode, the yellow one at 10:16 doesn't look like a small signal diode to me. It looks like a low value Zener diode. Oh yes, at 10:28 we can clearly see 3V3 on the side of it. Get the right part fitted. Maybe even think about looking at the schematic.
I did look at the schematic and all the diodes where marked as 1n144 I think 🤔 of top of my head but don’t correct me on that. :) I will put a link to the schematics if any one want to take a look at them in them description :)
Are you missing a cap under the left most of those hot 3 chips (under the red mains cable)? Also, check all the caps over their pins for continuity, if the meter beeps, it's a bad cap. TBH, all the components are pretty ancient, so could be any number of them being bad. The resistor array, you can check for ohm-age from the common pin to each of the others to make sure they're all the same value and correct as to whatever marking it on it. The 68008 is an 8/32-bit cpu like the 68000 (which came before), Motorola's releases had even chip numbers.68008, 68010, 68020, 68030 (apart from this one), 68040, 68060. Also, your discord invite is invalid.
Thank you for such detailed information. I’ll check out for a missing cap like you said. And also check out the resistor array like you said. At the moment all the caps are beeping which is what made me think I had a short well all the caps as in the ceramic ones. I’ll recheck the discord and update it thank you :). But will probably be tomorrow now. Thanks for the comment
Is this related the BBC micro's "Tube"? Or is it a different way to add a second CPU to the Beeb? Is it useful for things other than OS9? Can it run any old OS9 apps or do they have to be specially compiled OS9 apps for this specific system?
Hi this plugs directly into the beeb cpu socket not through the tube. The bbc cpu then plugs into this. It comes with some os9 apps office based stuff. I can’t 100% answer it he question on OS9 software. But when I get it working I’ll deffo try this for you. It’s all new to me the os9 and also the device :) thanks for your comment
@@Retro4u Thanks and No worries. I don't think I've ever touched a beeb but I've been getting more and more interested in '80s machines with various CPU combinations, the TRS-80 models with a 68000 in addition to their Z80 is another interesting one. The Commodore 128 is maybe the one most people know. I very briefly played with OS9 on the Tandy Coco a few years ago while looking at all the '80s systems I had no personal experience with. Those guys seem to regard OS9 very highly. I'm not sure if their 6809 version and your 68000 version will have interesting differences.
@@andrewdunbar828 yeah it a great 👍 getting interested in the 8bits Coco I’ve never used being in the UK. 🇬🇧 we had the dragon I have vague memory’s of that as a child. I’m still learning and enjoying this as a hobby. But have worked in the of repair and laptop industry.
OS-9 is has real hardware abstraction. This would specifically be OS-9/68k (sometimes called OSK). It should run a lot of OSK software not compiled for the particular system. Normal display is usually a serial protocol and looks like you are talking to a terminal. I am mostly familiar with OS-9/6809 and NitrOS9 (a re-implementation that has a version to take advantage of the extended features of the h6309)
@@Retro4u its true though...a 32bit processor family, with 32bit instructions, internal registers and internal data bus its bad enough having the "crippled" 68000 with its 16bit external data bus, but to go one step to an 8bit databus...I think "learning difficulties" is quite appropriate hehe
In an 8 bit era however, it was the difference between having one or not having one, since all the presumably cheaper 6800 series chips would work with it. I would of loved to have one in the early to mid 80's ... I'm gonna say no worse than an 8088 running at 4.7MHz
Oh FFS, 35 Ω is NOT a short circuit. Your (coming soon) milli Ohm meter isn't going to help. You seem to struggle to use your DMM. Slow down. Think about what you want to measure, select an appropriate range and then probe. When measuring the '5 Volts' you selected the 200 Volt range rather than the 20 Volt range. When changing from continuity to Ohms you select the 2kΩ range instead of 200Ω. When using the Ohms range you seemed to misunderstand the display. 0.036 (20:02) is not "zero point three six" it's "zero point ZERO three six kay Ohms" i.e 36 Ω, just like it was at 19:52.
@@Brian_Of_Melbourne lol 😂 well thanks for the detailed help. :). As I said I’m still learning and that why I asked for help on the 0.35ohm short. Which you have helped me with and I’m grateful yeah I noticed I selected the wrong range on the meter for measuring the voltage but sometimes I’m trying to concentrate on the camera 📷 and recording these things happen. lol. But again thanks you for your knowledge and help I will read it and take it in. Least I didn’t say 68000 this time. Thanks for you comment :)
@@Retro4u It's a 35 Ω situation, not a "0.35ohm short". If it were 350 mΩ that would be a lot closer to a short circuit, being two orders of magnitude less. Concentrating on the camera to the detriment of basic accuracy with numbers and values is something that perhaps needs addressing. If the camera's not right or the numbers get jumbled up then "cut" and go again.
Great to see the beeb getting some love.
Maybe not the ultimate, but certainly very close to an ARM1 :)
Interesting that they didn't go for the TUBE, but for faster disc access, it makes sense.
Love the beeb computers such a big part of my life. 😊 yeah interesting approach they did kind of 2 computers in one thanks for the comment
Yellow diode is a zener, 3.9v, an essential part of the voltage regulation circuit. A regular small signal diode like 1n4148 there will cause dangerous overvoltage. Put the correct component like 1n4730 or 1n5915 there and it should work. Cheers!
Thanks for that I was reading of the schematic which I struggled to find and could only find a 1n listed around the battery area I’ll get this removed and order the other. Thankyou so much for your comment and help
You are absolutely right. It IS a 3.9 Volt Zener. Sorry for the confusion.
@Brian_Of_Melbourne yep just found it on the diagram and ordered one will get it changed :) thanks all for your help :)
Yeah. These painted diodes are usually Zeners.
That bad boy wants replicating ;) ... nice bit of kit there, buddy 😉
Thanks 👍I will of course contact you about this later. Could be a interesting 🤔 project :) thanks thanks for the comment
The 68000 (60008) was the holy grail of cpu's back in the early 1980's
It’s amazing how many of these where around and used in different machines I’m learning more and more. The QL has the same cpu as well and I think the early Atari st although I could be wrong. Thanks for your comment
Yep I was about 14 and programming my Sinclair Spectrum in Z80 machine code and had a friend in the software industry telling me details about the 68000 and the Amiga. Everything just sounded amazing - so many registers!
@andrewdunbar828 yeah it was a huge leap from the 8bit era. I remember seeing and hearing the Amiga for first time and was dumbstruck lol 😂. Seems we don’t have that leap anymore :) thanks again for your comment.
Very interesting looking board. I hope you get it working. Try taking the bigger chips out and retesting the voltage. I think it's more likely to be one of them than a dead short (the resistance is too high for a short anyway). You can also check the resistance of those arrays by probing from the common pin to each of the others.
Thanks Tim. Yeah will revisit it this week would be good to see this board working again. I’ll remove the chips that can be :) Thanks for the comment
Tantalum caps often fail short rather than open and are always worth a check.
Thankyou will certainly give it another look over when I have the new meter next time 🕰️ will be sure to look over the caps. Thankyou for the comment
Came here to mention tantalum and was beaten to the punch :)
Indeed, tantalum bead capacitors do fail short circuit, they don't fail to 35 Ω. It may be worth briefly removing the two tantalums to confirm that they are OK with your little tester, then they can go straight back in.
Do you, @retro4u, know which ones are the tantalum bead capacitors?
@Brian_Of_Melbourne yeah 👍 they the little orange ones. I’ll remove them like you said and see if it makes any difference. :)
@@Penfold42thankyou will remove these and give them a look. Thanks for your comment these have been mentioned a few times so so certainly worth a look :) 😊
Hello! Interesting board, I hope you get it working. :-)
I’m sure it will be working soon. The battery 🪫 damage wasn’t so bad so I’m sure we have hoops and I’ve had lots of tips and hints of people on here. Thanks for the comment.
@@Retro4u I'll be along for the journey!
@Jimbaloidatron thank-you :) much appreciate
without having a circuit diagram its hard say if 35 omhs is low, but since you are not getting 5 volts (I assume) that clearly implies something is gone (technically 35 omhs isn't a short) you should remove all the socketed chips and see if your 5 volt line returns... you tend to get low resistivity from/near power supply circuits (analog circuits)... so provided the board was disconnected from its PSU while measuring, the omh reading does seem low for a digital board, that said, there does seem to be analog circuity in lower left quadrant of this board, but your thermal imaging doesn't show much heat coming from this area... touch tests might be better than your thermals as no digital IC from this era should be so hot that can touch them for at least couple second... if you can touch for a split second that implies a bad chip.
Wow thanks so much for such a detailed explanation. I will of course try pull all the chips I did think that pull the socketed ones. That will be a job for next week for sure. There is a circuit diagram out there but it’s hand drawn and I struggled to read some of it plus I’m still not 100% on reading it. I found the cap ect by tracing from the battery. Thanks again for your comment and help it’s gratefully appreciated 😊
@@Retro4u that should have read "can't touch" x2
IBM had only OS/2. This thing has OS9! It has to be over 4 times better!
68008 CPU is a weird beast. It runs 32 bit code on 16 bit internal architecture with 8 bit external bus. Someone should interface it with QSPI (4 bit) memory.
lol 😂 love the 4 times better should have used that in the video. Yeah strange cpu probably why Sinclair used it lol 😂. Thanks for sharing he comment
Thanks
Many thanks for this. Will put it towards some equipment :)
I emulated this board in MAME a few years ago, so know what to expect when you get it working. I've never seen a real board running, only my emulation, and doubt anyone else has either in likely over 20 years! A surprising amount of documentation exists for this board, including schematics, which I presume you've found?
So your board didn't come with the ROM, presume you have the OS9 floppies or have you downloaded those too?
@@ngbarnes I have a full set of disks originals and backups :). Yeah I found the schematics just and the installations guide. I’m looking forward to getting it work of course but only a matter of time I think 🤔 these things are sent to test us :) So cool that you emulated this. I have no idea what to expect lol 😂 thanks for the comment
@@Retro4u whilst there are images of the disks out there I'd appreciate seeing your originals imaged too, with photos, for comparison as it's not obvious which are original and which have been modified. Just want to have a clean set of originals imaged.
@@ngbarnes will do for sure next video. :)
You can try a Motorola 68HC001. It's a PLCC 68000 on which you can select 8 bit and 16 bit mode with a hardware pin. This would allow to run an Amiga 600 with 8 bit.
Interesting 🧐 I’ll look into that :)
@Michael.Werker How would that work exactly? Are you suggesting a whole new PCB with the appropriate PLCC-68 socket and the inevitably slightly different support circuitry? Or maybe an adapter board that adapts the PLCC-68 to the DIP-40? If that is the case, then there'd only be an 8-bit bus so the 16-bit capability of the 68HC001 would be unavailable.
You can't run an Amiga 600 with a 68hc001 running in 8 bit. The rest of the computer relies on 16 bits, you wouldn't be able to get the chipset to do much if you can't write to upper 8 bits of it's registers
@@Brian_Of_Melbournethe mc68sec000 can also run in 8 bit mode. I assume the suggestion was if you needed to replace the 68008 or build a new board. Though running in 8 bit mode is a terrible idea. It basically halves the performance. Fitting 16 bit ram and ROM is a better option
@Brian_Of_Melbourne If Pin 8 of the 68HC001 is GND, then the processor is in 8 bit mode after reset. I also tried to find a suitable PLCC/DIP-Adapter, but wasn't successful.
@phil6859 I know that an Amiga won't work in 8 bit mode, but it should result in some interesting crashes :-D
The capacitor you finished soldering at 10m, I could not fully tell but it looked as though both sides were soldered to the same track or one track was close to the other.
Will check but thanks for heads up. I think the tracks are very close but I’ll recheck that pint good shout. Thanks for the comment :)
When you power it up, at around 21:15, your PSU shows 5.05 Volts, but when you measure this on the PCB, right where the PSU is connected, then you get 3.5 Volts. So a volt and a half has vanished IN THE WIRES FROM THE PSU. Let's do the calculation (Ohm's Law). R = V / I. 1.5 V / 0.7 A = ~2.1 Ω. That's too high for connecting leads, by two or three orders of magnitude. Measure them, individually, with your (soon come) milli Ohm meter. My bet is that one lead will be passable and the other will be contributing most of the 2.1 Ω. They'll be unreliable crimps that need to be properly soldered.
@@Brian_Of_Melbourne I will check this as well later. Again thanks for your comment. And huge help :)
@@Retro4u Start with the common lead on your DMM (set to the 20 Volt range) fixed soundly on the negative terminal of your PSU. Then you can measure the voltages at the PCB (nominally 0 Volts and +5 Volts) to see where you're at. It may be helpful at this point to make a lead with a decent crocodile clip on one end and a 4 mm banana plug on the other for activities like this.
Further testing you can do to look at the power draw across the PCB is the set your DMM on 2 Volts, connect the common lead to where the 0 Volt connection is on the PCB. Then probe around on the various 0 Volt points on the PCB (like the 'ground' pins on various chips, etc). You may find some points are higher than others, these are points where the current flowing in the PCB tracks and the resistance of those tracks is leading to a voltage drop. You can do the same with the +5 Volt trace(s).
Power rail is obviously shorted , I would start check the two tantalum caps , 2 orange blobs between the big chips and also down by the plug / cutout square, they are notorious for failing and blow up itself or power supply. Bit concerned with 2 chips getting so toasty but that might be normal, also the resistor pack getting so hot dont seem normal but its obviously not the resistors fault , it would be something shorted if that is not normal, not sure what they do, might also be normal. I would start desolder both tantalums and see if that changes the reading from 36 ohms, and also I sure hope you replaced the diodes with the proper ZENERdiode voltages and not just normal diodes
Yeah I’ve order the diodes. Some people are saying they are short some not. Yeah 👍 I plan to remove the tantalum caps and test them seeing it sorts it out. Yeah I thought that about the resistor array I will check that out with readings later as well. :) thank you so much for the suggestions and detailed help it’s much appreciated and thanks for the comment t
@@Retro4u zeners are finicky. I heard moisture can cause them change value making them look fine but give wrong voltage so checking all voltages is always a good idea.Also they are a common failure. repairing amplifiers I already had to replace a handful of them. running a 4148 diode instead of a zener will forcefeed something 5v that wants 3.9volts making whatever that is very unhappy, I could not read the red markings but the yellow diode was a 3.9v zenerIts important to always use the right kind of diode , some places need a germanium diode and wont work right with a silicon one with different forward voltage.. Rifas is another common fail , they split , soak in water from air and go kaboom .amazing amount of smoke just one tiny rifa can make, one from old scope blacked out my whole second floor, it seemed to run fine for a minute and then full pompei..... Probably good idea replacfe any rifa with polyprop x or y cap and any tantalums with perhaps ceramic ones, they are much lower esr resistance , in some cases that matters but I doubt it matter here. I had an old pc mainboard totally short out a rail with over a dozen tantalums, removed them one by one to test out of circuit, even with milliohm meter u might not see if the one next door or the one measured is bad, rails are supposed to be low impedance. Often rifas look fine until being on a a few mins. (evil buggers) and best is they always hide deep inside power supplies where u cant see them until they go, can have hidden cracks on underside etc old rifas is always a bad thing.
@kristiansolstad9068 yeah experienced many rifas and magic smokes with the apples and bbc power supplies. After what you said I’ll probably just replace those caps to be certain there is only a few of them. Just need to find out what rating they of the schematic :) thanks again for such a detailed explanation and help :)
@@Retro4u the x2 / y or whatever is probably best bet in mains filters, one fail short the other fail open and theyre safety caps. any mains filter cap wont matter if open or missing , just a bit more theoretic noise. value should be on then tho I have seen them with sides missing etc ;) Sometimes diagnose is easy I saw a couple circuits boards with giant holes with one half leg remain , one was a big motor device the other high voltage part of a tv , the 3 inch gaping hole gave me a small clue to start diagnose ;) got the tv for free coz it was "blown up with fire and obvious could not be repaired" then again a 50 cent 1250v discarded cap from my junk pile (was given to me for being "unsafe" / recalled) made it work for decades more, until someone stole it. always fun when you have to guess where tracks was supposed to have been .... semiconductors can be hard to diagnose, sometimes they split in half other times look fine and are bad and you cant find out until running them in a circuit with load. zeners f.ex wont give the right voltage if current is way off. The really fun ones are intermittent so every test they measure and perform perfect and then randomly fail. Parts can also look like crap and work fine... Ceramic / polyprop / plastic caps seem to work forever or until someone break them in half.
@kristiansolstad9068 yeah tbh I lot of the ceramic caps I replaced where either damaged or I loved them and they snapped lol 😂. I’m sure with all this info I’ll be able to get this board up and running again. I just need to source these caps of the drawing ✍️ I find it hard to follow lol but managed to find the diode and it was 3v9 so ordered one. I’m still learning this stuff and you have been a great help. :) table yet again
For reference a short to ground is very unlikely to be a ceramic cap, when they fail open circuit, effectively just removing the cap from the circuit. Tantalum caps on the other hand fail closed and create a short. Electrolytic caps tend to fail open circuit. You do have a tantalum cap in the middle lower section, right next to the "cut out"
Do I need to point out that the TRS80 image you used is not a COCO, it isn't even a TRS80... The CoCo computers look relatively similar to the Dragon in either black/silver or cream cases
@@julianbrown1331 hi 👋 thanks for the comment in the next video I removed the tants and found 1 faulty one. Tbh Ive never even seen a coco and that pic a was a from a site talking about them so they must be wrong as well but good spot. Dragons I saw as a child. I’m still working on it but getting closer thanks for your help and comment
That second diode, the yellow one at 10:16 doesn't look like a small signal diode to me. It looks like a low value Zener diode. Oh yes, at 10:28 we can clearly see 3V3 on the side of it. Get the right part fitted. Maybe even think about looking at the schematic.
I did look at the schematic and all the diodes where marked as 1n144 I think 🤔 of top of my head but don’t correct me on that. :) I will put a link to the schematics if any one want to take a look at them in them description :)
@@Retro4u Yep, there it is in the schematic - D1 3.3 Volt Zener diode and D2 & D3 are 1N4148.
Are you missing a cap under the left most of those hot 3 chips (under the red mains cable)? Also, check all the caps over their pins for continuity, if the meter beeps, it's a bad cap. TBH, all the components are pretty ancient, so could be any number of them being bad. The resistor array, you can check for ohm-age from the common pin to each of the others to make sure they're all the same value and correct as to whatever marking it on it.
The 68008 is an 8/32-bit cpu like the 68000 (which came before), Motorola's releases had even chip numbers.68008, 68010, 68020, 68030 (apart from this one), 68040, 68060.
Also, your discord invite is invalid.
Thank you for such detailed information. I’ll check out for a missing cap like you said. And also check out the resistor array like you said. At the moment all the caps are beeping which is what made me think I had a short well all the caps as in the ceramic ones. I’ll recheck the discord and update it thank you :). But will probably be tomorrow now. Thanks for the comment
Is this related the BBC micro's "Tube"? Or is it a different way to add a second CPU to the Beeb? Is it useful for things other than OS9? Can it run any old OS9 apps or do they have to be specially compiled OS9 apps for this specific system?
Hi this plugs directly into the beeb cpu socket not through the tube. The bbc cpu then plugs into this. It comes with some os9 apps office based stuff. I can’t 100% answer it he question on OS9 software. But when I get it working I’ll deffo try this for you. It’s all new to me the os9 and also the device :) thanks for your comment
@@Retro4u Thanks and No worries. I don't think I've ever touched a beeb but I've been getting more and more interested in '80s machines with various CPU combinations, the TRS-80 models with a 68000 in addition to their Z80 is another interesting one. The Commodore 128 is maybe the one most people know.
I very briefly played with OS9 on the Tandy Coco a few years ago while looking at all the '80s systems I had no personal experience with. Those guys seem to regard OS9 very highly. I'm not sure if their 6809 version and your 68000 version will have interesting differences.
@@andrewdunbar828 yeah it a great 👍 getting interested in the 8bits Coco I’ve never used being in the UK. 🇬🇧 we had the dragon I have vague memory’s of that as a child. I’m still learning and enjoying this as a hobby. But have worked in the of repair and laptop industry.
OS-9 is has real hardware abstraction. This would specifically be OS-9/68k (sometimes called OSK). It should run a lot of OSK software not compiled for the particular system. Normal display is usually a serial protocol and looks like you are talking to a terminal. I am mostly familiar with OS-9/6809 and NitrOS9 (a re-implementation that has a version to take advantage of the extended features of the h6309)
@@AlexEvans1 interesting 🤨 will have to try some other software when it’s up and running I myself know nothing about OS9 lol 😂
@Retro4u you from Leeds?
Staffordshire but I got to Leeds amongst meets sometimes. Thanks for the comment
the 68008 isn't the younger brother of the 68000 family
its more like the brain damaged sibling with learning difficulties
lol 😂 that’s one way to put it. But thanks for your comment :)
@@Retro4u its true though...a 32bit processor family, with 32bit instructions, internal registers and internal data bus
its bad enough having the "crippled" 68000 with its 16bit external data bus, but to go one step to an 8bit databus...I think "learning difficulties" is quite appropriate
hehe
@@kwanchan6745 And that's why the Sinlcair QL didn't quite live up to its promise
@@kwanchan6745 yeah I get that a bit of a bottle neck tbh lol 😂. But it made it compatible with the 8 bit systems I guess. Thanks for the comment :)
In an 8 bit era however, it was the difference between having one or not having one, since all the presumably cheaper 6800 series chips would work with it. I would of loved to have one in the early to mid 80's ... I'm gonna say no worse than an 8088 running at 4.7MHz
Oh FFS, 35 Ω is NOT a short circuit. Your (coming soon) milli Ohm meter isn't going to help. You seem to struggle to use your DMM. Slow down. Think about what you want to measure, select an appropriate range and then probe. When measuring the '5 Volts' you selected the 200 Volt range rather than the 20 Volt range. When changing from continuity to Ohms you select the 2kΩ range instead of 200Ω. When using the Ohms range you seemed to misunderstand the display. 0.036 (20:02) is not "zero point three six" it's "zero point ZERO three six kay Ohms" i.e 36 Ω, just like it was at 19:52.
@@Brian_Of_Melbourne lol 😂 well thanks for the detailed help. :). As I said I’m still learning and that why I asked for help on the 0.35ohm short. Which you have helped me with and I’m grateful yeah I noticed I selected the wrong range on the meter for measuring the voltage but sometimes I’m trying to concentrate on the camera 📷 and recording these things happen. lol. But again thanks you for your knowledge and help I will read it and take it in. Least I didn’t say 68000 this time. Thanks for you comment :)
@@Retro4u It's a 35 Ω situation, not a "0.35ohm short". If it were 350 mΩ that would be a lot closer to a short circuit, being two orders of magnitude less. Concentrating on the camera to the detriment of basic accuracy with numbers and values is something that perhaps needs addressing. If the camera's not right or the numbers get jumbled up then "cut" and go again.