For the take-apart, it's best to remove the cover on the display panel between the hinges and disconnect the ribbon cable at that end - leaving it still connected on the motherboard. Much easier to reconnect on reassembly! They are famed for damage on the back-side tracks of the keyboard where it rests on the plastic casing when assembled and in use, and gradually wear away, so many need a bit of bodging too. And of course they're prone to corrosion from battery leakage. I have one of these I use regularly. Great to type on, and an excellent 'distraction free' system. Mine has a 'REX' option ROM in it that adds extra memory pages for non-volatile backups and workspace, plus space to save and use original option ROMs which in the day provided lots of extra software and connectivity options. Makes this quite a versatile little system with maybe 12-15 hour run time on a set of 4 AA batteries. Sadly, the polariser does tend to need replacing after all this time in order to get the original screen contrast back, but there's a chap on YT with a video showing how that's done for anyone wanting to find out how! Great machine, and excellent video!!
Used to work for a daily newspaper in Europe at the time. We gave those to our reporters in third world countries. They were always able to transmit their texts with the 300 baud acoustic couplers. Correspondants from other papers with new-fangled laptops had to dictate their papers on the phone. If they were even able to charge them (not working on 4 AAs you can get anywhere), they couldn't connect their modems or, if they managed to, couldn't switch down to a speed that would work on those noisy phone-lines ... Even today, a Tandy 200 is a remarkably useful tool in such dire circumstances ;-)
I've had this before, it's the caps reforming. They don't like not having voltage on for a long time, hence the no boot. But only a few power cycles and the caps are much better. I got a fairly high end synth for cheap like that. It was stuck in no boot for more than a few minutes when I got it, then it just booted. After power cycling it comes up straight away. But if you don't use it for longer than a week or so I have to wait all over again. No battery inside.
Interesting! Got this on my modern PCs power supply. When I was a few days out it got stuck in a start cycle, after a little while it worked again, even the day after also. I head a thermal issue in mind and try to chase the bad components with a heat gun and ice spray without success. Dose anyone know what is responsible for this effect? 🤔
I loved my Tandy 2000 desktop. Tandy color was the shit. I have great memories of the games I played both by myself and with my brothers. It's a great feeling when an old, nostalgic piece of kit fires up. 👍
"Hello IT? My computer is working when I turn it on" "Ah have you tried turning it off and on again until it breaks?" Only Dave can be upset when he switches something on and it works fine. 😄
Over time, the polarising sheet in the display can fade/ go bad. It's common in old LCD handheld games. It can be remedied by grabbing a polarising sheet from a broken TV and (after finding the correct rotation) cutting and fitting a replacement one.
I bet you can 3D print a battery cover for that pretty easily. The first thing I thought of that would be a great use of 3D printers when they came out was printing battery covers. I guess so did others because there's a ton on eBay.
I think that the clicking cycling fault must have been caused by an electrolytic capacitor that was reforming itself after not seeing a polarising voltage for a long time.
I had both the Model 100 and 200. I used them for a data acquisition system reading. recording and displaying the data with a graph display. It was set up to record four pressure transducers. I also had the 3.5" Portable Disk Drive. I mounted it all in a brief case for remote use. Great machines for the day.
Years of no power probably meant the nicad pack was totally at zero and initial battery voltage pulled too low by it causing your no boot and clicking. You could try a 100 ohm resistor clipped across the nicad for a day or two with no batteries in, then try again. Some commenters suggest caps being the issue, but the caps seem too small to take any 'reforming' time. I expect if you had left it long enough the clicking would have stopped and it would have booted.
That's why these computers are legend, people can trouble shoot or even re-create it base on the service manual and a bit of reverse engineering after many years!
Don't remember that one, but I remember riding my bike up to the Hornsby Tandy and playing with the TRS80, whilst revelling in the Kraftwerk blaring out their large Hi-Fi speakers. Fun times indeed
Peaking signals you want an analogue meter. You can still buy them including centre zero varieties. Yes I have some quite high precision bench DMMs but they are hopeless with changing signals.
Ah I know nothing about it but maybe the nicad is for the cmos settings and the AA? cells are for the DRAM? It could have reset the cmos settings after the first boot.
If it is anything like the 100, the Varta battery is critical to powering the memory. After having it in storage, the Vartan is fully discharged, and it needs some time to charge or the voltage on the memory will be too low. When you put it in storage, make sure to flip the switch on the bottom to turn off the memory protection, taking the load off the varta.
I'm pretty sure that the TRS-80 Model 100 and 102 and the similar Kyocera designs (by NEC, Olivetti, and Kyocera/Kyotronic) didn't start without the NiCad battery, either. So, if there isn't any charge…
8085, surprised they didn't stick with the Motorola line for this one. 6803 or the like. The 256 byte integrated SRAM thing is usually a good sign they've gone with a CPU that requires '0 page' RAM since the CPU has more or less no general purpose registers onboard.
If you had the memory power switch off and turned on the machine, it would hiccup, the main power rail VR would charge via J302 and R165 until it started up, then discharge due to the load until undervoltage lockout powered it off again. Or maybe R165 is low enough to keep the main power rail up, but the processor boot loops due to the RAM chips being without power, as the internal battery was completely empty (this would happen even with the memory power turned on). J302 and R165 are for charging the internal AA batteries from the external power input, if you remove J302 you can use non-rechargeable AA's.
plz do more teardowns of old computers like this! i think ya supposed to reset it while its off..otherwise the sdram still gets power...reset button on the back should disconnect the power from the battery to the sdram
There's a famous picture of Annie Lennox and Dave Stuart on a train. Annie is typing on a Tandy 200... I got one recently but its missing the LCD hinge cover that sits in the middle. Don't think it works though. Need to dig it out and give it a try.
In my experience demonstrations never work either LOL. You spend hours setting up a system demo, test it multiple times, even just before the customer turns up and then bam and you end up swearing blind that it was working just before hand haha. Or the converse like you, trying to debug a fault that always occurs and as soon as the DUT (device under test) senses a scope in its vicinity it starts bloddy working again HAHA. Love that service manual - gone are the days IP was publicised. Probably the CPU regs held onto some invalid state during brownout preventing processor startup.
The last computer I owned that had a similar manual was an Amiga 500. Not sure if there was operation details or similar, but I remember it had the full schematics. Other than that, only micro controllers nowerdays with schematics :( ok, I don't have the equipment to fix a modern computer main board or graphics card and not sure if I can diagnose faults there, but schematics and board views would be nice anyway. I don't want to have the old 8/16-bit times back when it comes to performance, just the documentation like back then.
The Varta went open circuit, you're reading the voltage across the AA batteries(through a resistor), probably what caused it not to power up the first time, until it unshorted itself by going open, unless their is a bad cap somewhere..., but that's just my guess... take it with a grain of salt, lol
@@bn880 knowing a thing or two about batteries helps... if that was a nmc lithium cell (which the nominal voltage and initially measured 4v2 (typical terminate charge voltage) would suggest (but i do not think that nmc is THAT old of a battery chemistry...) then i would assume that battery to be fully charged and the voltage dropping over time is known as relaxation. edit: nicd -- dropping to 1v6 looks like a high esr thing
lol, what a joke both of you, he's measuring the varta voltage multiple times, it's not open circuit, it doesn't have protection to even go open circuit
good old times with that kind of documentations. FOr PCs, For Oscilloscopes, etc. Non of them today, best a short handbook for instruments or a link to a homepage which vanish soon ... today no schematics anymore instead scrubbed of letters etc. Only the gate array carries the "secrets" of this nice device ...
I cut my teeth on the Tandy 102 (similar, with half the screen height), bought new for over $500 in the early 1990s in high school. After tiring of BASIC games, I learned assembly language and wrote my own assembler, then optimized graphics (it's awfully slow). Eventually I added another bank of 32K RAM, all soldered in, and wrote a debugger with an added interrupt switch to enter it anytime. Also used it to interface to all sorts of hardware projects over the years. I had gotten the service manual and read it from cover to cover many times. Really educational stuff back then. I eventually wrote an emulator for it to run my old BASIC games on the PC. I got my money's worth.
I wonder if they had pick 'n place machines back in the day or were all the surface components hand soldered. Bad batteries in my experience will shoot right up to charge voltage for a little while. After a while, they pull the charger right down to nothing. Solution: Replace the battery.
processor will crash and restart if it experiences any sort of transient voltage drop while in operation (on some modern processors if running at full load 10mV drop is enough to do it ) Intel and Micron are the only part suppliers I work with today that provide proper documentation. Though they very clearly remove sections that would have to be documented internally in the manuals they circulate to customers. Micron ironically provides ONLY theory of operation + interface protocols. ACTUAL operation is considered a trade secret.
RE: "Manuals not having theory of operation anymore" -- That's from an era where you could actually see busses and stuff like that that were meaningful on the board. That has an 80186, which casual googling suggests is 10x10mm and 50'000 transistors, or 500 transistors/mm^2. Modern TSMC is 224'000'000 transistors/mm^2. Let's say for the sake of argument between the SRAM, display driver, etc., there are 3 times the CPU's transistors, this whole thing fits in 6.7e-4 mm^2. Or put another way, you could fit almost 1500 of them on a single mm^2 on a modern process!
I know that power supply ticking sound..."tick tick tick tick tick aaaand POP" like a pimple as it blows through whatever was shorting the rails. Bad decoupling cap somewhere maybe?
I'm not really a hardware guy like you, but I enjoy the channel because I learn... some of it must be rubbing off, because when you said the battery light latches, I thought, makes sense, because once the voltage gets low enough to trigger the battery light on, might as well latch it so that it doesn't flicker on and off when it's 'on the edge' voltage wise.
With the thumbnail of the video with the head on the side and tongue out I just had to click on it. I've got a dead Amstrad Notebook NC100; anyone in Oz (Brissy), interested? nb It has the battery cover.
For the take-apart, it's best to remove the cover on the display panel between the hinges and disconnect the ribbon cable at that end - leaving it still connected on the motherboard. Much easier to reconnect on reassembly!
They are famed for damage on the back-side tracks of the keyboard where it rests on the plastic casing when assembled and in use, and gradually wear away, so many need a bit of bodging too. And of course they're prone to corrosion from battery leakage.
I have one of these I use regularly. Great to type on, and an excellent 'distraction free' system. Mine has a 'REX' option ROM in it that adds extra memory pages for non-volatile backups and workspace, plus space to save and use original option ROMs which in the day provided lots of extra software and connectivity options. Makes this quite a versatile little system with maybe 12-15 hour run time on a set of 4 AA batteries.
Sadly, the polariser does tend to need replacing after all this time in order to get the original screen contrast back, but there's a chap on YT with a video showing how that's done for anyone wanting to find out how!
Great machine, and excellent video!!
Used to work for a daily newspaper in Europe at the time. We gave those to our reporters in third world countries. They were always able to transmit their texts with the 300 baud acoustic couplers. Correspondants from other papers with new-fangled laptops had to dictate their papers on the phone. If they were even able to charge them (not working on 4 AAs you can get anywhere), they couldn't connect their modems or, if they managed to, couldn't switch down to a speed that would work on those noisy phone-lines ...
Even today, a Tandy 200 is a remarkably useful tool in such dire circumstances ;-)
I've had this before, it's the caps reforming. They don't like not having voltage on for a long time, hence the no boot. But only a few power cycles and the caps are much better. I got a fairly high end synth for cheap like that. It was stuck in no boot for more than a few minutes when I got it, then it just booted. After power cycling it comes up straight away. But if you don't use it for longer than a week or so I have to wait all over again. No battery inside.
Possible.
@@EEVblog the 8085, 81C55 combination also made sense, it's a port expander, seen it in the Korg Poly800
Interesting!
Got this on my modern PCs power supply.
When I was a few days out it got stuck in a start cycle, after a little while it worked again, even the day after also.
I head a thermal issue in mind and try to chase the bad components with a heat gun and ice spray without success.
Dose anyone know what is responsible for this effect? 🤔
I would LOVE to see someone develop a way to interface a monochrome OLED panel to replace the old LCD ones. Imagine, finally readable! 😅
I loved my Tandy 2000 desktop. Tandy color was the shit. I have great memories of the games I played both by myself and with my brothers.
It's a great feeling when an old, nostalgic piece of kit fires up.
👍
Just like Adrian Black (Adrian's Digital Basement) always says, computers always mystery repair themselves after fail, reason unknown.
Glad it's not just me.
"Hello IT? My computer is working when I turn it on"
"Ah have you tried turning it off and on again until it breaks?"
Only Dave can be upset when he switches something on and it works fine. 😄
Wow, this portable computer sure looks fine even though it is 2 months older than me :D
Heck yeah! Been waiting to see the repair of this beauty :D
"Repair"
@EEVblog Yeah. Was still fun to watch tho
Back in the day, I worked part time at an Acorn Computers service centre. The tech manuals for their machines were fantastic.
Eevblog does retro computing!? Awesome!
You must be new here, welcome! th-cam.com/play/PLvOlSehNtuHu7M4SgYSh8-tc2fd6CYqGi.html
Definitely reminds me of my home brew days in the 70s and early mid 80s before work took over.
Over time, the polarising sheet in the display can fade/ go bad. It's common in old LCD handheld games. It can be remedied by grabbing a polarising sheet from a broken TV and (after finding the correct rotation) cutting and fitting a replacement one.
Hey Dave! That board is a very early example of surface mount technology! I'm sure you knew..👍😀
Neat layout on this PCB and what a maintenance manual 😀.
I bet you can 3D print a battery cover for that pretty easily. The first thing I thought of that would be a great use of 3D printers when they came out was printing battery covers. I guess so did others because there's a ton on eBay.
Yeah, except that my 3D modelling skills suck
I think that the clicking cycling fault must have been caused by an electrolytic capacitor that was reforming itself after not seeing a polarising voltage for a long time.
@25:19 Did you see how Dave reacted to the flippy floppies !!! 😂😂😂😂😂😂
I had both the Model 100 and 200. I used them for a data acquisition system reading. recording and displaying the data with a graph display. It was set up to record four pressure transducers. I also had the 3.5" Portable Disk Drive. I mounted it all in a brief case for remote use. Great machines for the day.
14:28 That is NOT a Philips chip ! It is T.I. chip packaged in Philipines.
Brain fart.
Just needed the glow plugs to warm up a bit😅
Years of no power probably meant the nicad pack was totally at zero and initial battery voltage pulled too low by it causing your no boot and clicking. You could try a 100 ohm resistor clipped across the nicad for a day or two with no batteries in, then try again. Some commenters suggest caps being the issue, but the caps seem too small to take any 'reforming' time. I expect if you had left it long enough the clicking would have stopped and it would have booted.
"I'm sorry, son. I can't play catch right now. My caps are leaking."
Nice Video !!
Yeah Dave, My old brain can't always remember the old Tandy stuff, from 40+ years ago either. I can't remember why not?
That's why these computers are legend, people can trouble shoot or even re-create it base on the service manual and a bit of reverse engineering after many years!
Was confused about the Gatorade chip until I saw the service manual.
I've got one of those. Need to dig that out and play with it
"I swear it wasn't working yesterday, professor!"
Don't remember that one, but I remember riding my bike up to the Hornsby Tandy and playing with the TRS80, whilst revelling in the Kraftwerk blaring out their large Hi-Fi speakers. Fun times indeed
Peaking signals you want an analogue meter. You can still buy them including centre zero varieties. Yes I have some quite high precision bench DMMs but they are hopeless with changing signals.
Ah I know nothing about it but maybe the nicad is for the cmos settings and the AA? cells are for the DRAM? It could have reset the cmos settings after the first boot.
This was funny, You spent an entire video trying to break it instead of trying to fix it, haha!
The 8085 - not really upside-down. It's just that you're in Australia. The electrons don't fall out in the UK...
This is great. Do more retro stuff.
If it is anything like the 100, the Varta battery is critical to powering the memory. After having it in storage, the Vartan is fully discharged, and it needs some time to charge or the voltage on the memory will be too low. When you put it in storage, make sure to flip the switch on the bottom to turn off the memory protection, taking the load off the varta.
You could replace the old 3*1,2V Nickel-Cadmium Cell with a Li-Ion one from a one-way e-cigarette.
4,2 Volts fits perfectly ...
I'm pretty sure that the TRS-80 Model 100 and 102 and the similar Kyocera designs (by NEC, Olivetti, and Kyocera/Kyotronic) didn't start without the NiCad battery, either. So, if there isn't any charge…
Classic indeed
8085, surprised they didn't stick with the Motorola line for this one. 6803 or the like. The 256 byte integrated SRAM thing is usually a good sign they've gone with a CPU that requires '0 page' RAM since the CPU has more or less no general purpose registers onboard.
If you had the memory power switch off and turned on the machine, it would hiccup, the main power rail VR would charge via J302 and R165 until it started up, then discharge due to the load until undervoltage lockout powered it off again. Or maybe R165 is low enough to keep the main power rail up, but the processor boot loops due to the RAM chips being without power, as the internal battery was completely empty (this would happen even with the memory power turned on). J302 and R165 are for charging the internal AA batteries from the external power input, if you remove J302 you can use non-rechargeable AA's.
plz do more teardowns of old computers like this!
i think ya supposed to reset it while its off..otherwise the sdram still gets power...reset button on the back should disconnect the power from the battery to the sdram
There's a famous picture of Annie Lennox and Dave Stuart on a train. Annie is typing on a Tandy 200... I got one recently but its missing the LCD hinge cover that sits in the middle. Don't think it works though. Need to dig it out and give it a try.
Sure enough, I just searched for it and there it is, great pic! Wonder what she used it for?
i thought you are going to short the little battery with some resistore! that could be the ticket to replicate the issue!
In my experience demonstrations never work either LOL. You spend hours setting up a system demo, test it multiple times, even just before the customer turns up and then bam and you end up swearing blind that it was working just before hand haha. Or the converse like you, trying to debug a fault that always occurs and as soon as the DUT (device under test) senses a scope in its vicinity it starts bloddy working again HAHA. Love that service manual - gone are the days IP was publicised. Probably the CPU regs held onto some invalid state during brownout preventing processor startup.
Missing battery cover ?... That's the primary purpose for 3D Printers.
Yes, I suck at 3D modelling though.
@@EEVblog I hear that...
How about cutting out a rectangle of Plasticard ?
@@EEVblog There are several Tandy 200 battery covers on Thingiverse, no modelling needed!
The last computer I owned that had a similar manual was an Amiga 500. Not sure if there was operation details or similar, but I remember it had the full schematics. Other than that, only micro controllers nowerdays with schematics :( ok, I don't have the equipment to fix a modern computer main board or graphics card and not sure if I can diagnose faults there, but schematics and board views would be nice anyway. I don't want to have the old 8/16-bit times back when it comes to performance, just the documentation like back then.
I miss the "Made in Japan" days... because most everything I still have 30+ years later, still works! lol
hi Dave! Please recommend the best oscilloscope under $1000 in 2025. You once made a video about MSO5000, is it too outdated at this point?
Will the BM2257 be available in your US Amazon store at some point?
Ohh, new vid!
No 4K for our viewing pleasure........awwwww!
"I hate when it's too short" said the actress to the bishop.
"vintage computer window maker"😂😂😂😂hahaha LMFAO
The flat ribbon cable to the screen definitely has a limited number of bending actions left.
At least it's relatively cheap and easy to create new ones with JLCPCB , PCBWay etc. nowadays.
my First computers was a Radio Shack Model I with 4k memory and cassette tape drive.
You do not see floppy floppys like that anymore. Thongs ain't what they used to be 😅
And 1985 was the best year because?…….don’t worry I know, and you’re absolutely right Mr. Brown.
damn it Dave haven't you learned anything, "Don't turn it on! Take it apart!"
I'm a slow learner.
The Varta went open circuit, you're reading the voltage across the AA batteries(through a resistor), probably what caused it not to power up the first time, until it unshorted itself by going open, unless their is a bad cap somewhere..., but that's just my guess... take it with a grain of salt, lol
definitely not, he even removed the batts to measure the varta and you can see it dropping over time then
@@bn880 knowing a thing or two about batteries helps... if that was a nmc lithium cell (which the nominal voltage and initially measured 4v2 (typical terminate charge voltage) would suggest (but i do not think that nmc is THAT old of a battery chemistry...) then i would assume that battery to be fully charged and the voltage dropping over time is known as relaxation. edit: nicd -- dropping to 1v6 looks like a high esr thing
lol, what a joke both of you, he's measuring the varta voltage multiple times, it's not open circuit, it doesn't have protection to even go open circuit
good old times with that kind of documentations. FOr PCs, For Oscilloscopes, etc. Non of them today, best a short handbook for instruments or a link to a homepage which vanish soon ... today no schematics anymore instead scrubbed of letters etc. Only the gate array carries the "secrets" of this nice device ...
I cut my teeth on the Tandy 102 (similar, with half the screen height), bought new for over $500 in the early 1990s in high school. After tiring of BASIC games, I learned assembly language and wrote my own assembler, then optimized graphics (it's awfully slow). Eventually I added another bank of 32K RAM, all soldered in, and wrote a debugger with an added interrupt switch to enter it anytime. Also used it to interface to all sorts of hardware projects over the years. I had gotten the service manual and read it from cover to cover many times. Really educational stuff back then. I eventually wrote an emulator for it to run my old BASIC games on the PC. I got my money's worth.
I wonder if they had pick 'n place machines back in the day or were all the surface components hand soldered. Bad batteries in my experience will shoot right up to charge voltage for a little while. After a while, they pull the charger right down to nothing. Solution: Replace the battery.
400mW computer including the screen. That is impressive.
processor will crash and restart if it experiences any sort of transient voltage drop while in operation
(on some modern processors if running at full load 10mV drop is enough to do it )
Intel and Micron are the only part suppliers I work with today that provide proper documentation. Though they very clearly remove sections that would have to be documented internally in the manuals they circulate to customers. Micron ironically provides ONLY theory of operation + interface protocols. ACTUAL operation is considered a trade secret.
In this case it doesn't restart it just locks up.
@@EEVblog Makes me wonder if the "restart" in more modern chips is actually part of the mitigation and not actually part of the fault ;)
The thing came with the thing to repair the thing. 😁
A person who works in TV would have the EXACT OPPOSITE luck of that, especially an engineer.
RE: "Manuals not having theory of operation anymore" -- That's from an era where you could actually see busses and stuff like that that were meaningful on the board.
That has an 80186, which casual googling suggests is 10x10mm and 50'000 transistors, or 500 transistors/mm^2. Modern TSMC is 224'000'000 transistors/mm^2. Let's say for the sake of argument between the SRAM, display driver, etc., there are 3 times the CPU's transistors, this whole thing fits in 6.7e-4 mm^2. Or put another way, you could fit almost 1500 of them on a single mm^2 on a modern process!
You still need an analog power supply.
@@EEVblog That's true! These days they wouldn't describe that because liability :(
7:45 4xAA battery laptop
Like god intended.
Caps re-forming i expect after years turned off. I would replace them anyway given the age.
Cold Solder Joints...
I know that power supply ticking sound..."tick tick tick tick tick aaaand POP" like a pimple as it blows through whatever was shorting the rails. Bad decoupling cap somewhere maybe?
Nope, it's the buzzer giving a tiny reset glitch sound.
Damned electronics working when they're not supposed to...
Have you tried hitting it with a hammer?
Had me at auto-hold
trying to sell one of these with original box, manual, some accessories.
What are they worth these days?
@@EEVblog one on ebay for $300 but its not in the box.
@@JamesWattMusic Ask $500, collectors will pay a premium for the box.
4:26 omg he stolen the backlight from uncles Siemens, call for vintage police 🚓
Real men use the Radio Shack TRS-80, affectionately known as the trash 80...
Let me turn the lights off. LCD screen fungineer
I'm not really a hardware guy like you, but I enjoy the channel because I learn... some of it must be rubbing off, because when you said the battery light latches, I thought, makes sense, because once the voltage gets low enough to trigger the battery light on, might as well latch it so that it doesn't flicker on and off when it's 'on the edge' voltage wise.
Yes, latching is good. Just surprised it didn't have a hysteresis where it turned off.
Boots in seconds!
If it works, don't fix it ;)
If it’s fixed, don’t break it.
If one not scared making LCD driver, put Raspberry Pi inside.
2:54... Those Delusions come with age Dave....😉
Install Windows 11 on it Dave .. Another Middle Finger to Microsoft lol
With the thumbnail of the video with the head on the side and tongue out I just had to click on it. I've got a dead Amstrad Notebook NC100; anyone in Oz (Brissy), interested? nb It has the battery cover.
All this from a leather working company. 😂
What is that zesty ass thumbnail 😂