I really learned a lot from watching your excellent videos on the ZX81, thank you for doing them. I finally got my TS1000 working, I replaced the ULA with a vLA81, and that did not cure the problem, then I replaced the Z80 cpu and that cured it. Now it has a new ULA, CPU, and 62256 memory mod. I am going to order in a new keyboard membrane for it. Thanks again for your help. RJ
My TS1000 has a D4016C chip, DIP24, in there with the LK2 already jumpered. I'll be changing to a 62256 this week. I'm glad I watched this video first, one less pin to worry about. Thanks!
Yes I agree, fantastic work. After I finished Pimping Up my ZX81, I decided to do the same on a TS1000 that I have. I did the composite video mod, and got the K cursor just as on the ZX81, next I did the memory upgrade just as before and got the K cursor, only it takes a little longer to appear, next I did the power mod, and installed a new Z80 and again seemed to be OK with the K cursor, and let it sit for awhile to see it anything over heated. I then put on a new keyboard membrane and reassembled it. After reassemble I hooked it up and powered it on, up came the K cursor as before, so I tried out some of the keys, and to my surprise none of the key function at all. I took it apart and checked for +5 volts at all the locations and all seems OK, same for the 0 volts. I am at a loss, any idea what the problem could be? I am thinking the ROM? Any help would be appreciated. Thanks. RJ
@@thebyteattic I would have to say no, because it was broken at the connector. I went ahead and done the composite mod and got the K cursor, and the the RAM upgrade. I did cut the broken end off the membrane and tried it, but had no response, so I then installed a new membrane with the same result. Any thoughts?
Fantastic work! What a joy to have the genesis of your computer experiences back in such beautiful and functional form. Your girlfriend really added a master touch with her work on the badge. Indeed, better than original in so many ways, the personal touches not least among them!
I’ve designed a little PCB with an SMD 62256 chip on it, together with a decoupling capacitor and a 10K Ohm resistor on it and all the needed routing on the PCB itself, so no need to bend pins. The 10K Ohm resistor is put between pin 28 (+5 volt) and pin 27, it is to make HRG8 mode working. The ZX81 was my first computer too.
@@thebyteattic I will publish it on github soon. Might even sell them in small batches if these is demand. My first prototype had some errors. These are now fixed.
Muchas gracias, me he entretenido viendo las tres partes de la mejor restauración/actualización de un ZX81 que he visto, tengo un Timex Sinclair TS1000 a la espera de una ULA de reemplazo y un mod. de video, ahora estoy animado a hacerlo. Saludos desde Colombia. Thank you very much, I've been entertaining myself looking at the three parts of the best restoration / upgrade of a ZX81 that I have seen, I have a Timex Sinclair TS1000 waiting for a replacement ULA and a mod. video, now I am encouraged to do so. Greetings from Colombia.
Also, I found a 128K memotech from a donation store years ago. Still have it, not sure if it was for a TS1000 or TS2068. I think back then I plugged it into a TS1000 and it did a white blank screen. Maybe I even fried that board (ULA), I will be pulling it out of storage soon.
Great video, thank you for making it. I don't understand why the RAM isn't addressing the full 32KB, why only 16KB? I thought the ZX81 could address 64KB directly. Must have been covered in another video, I will check them all out. I look forward to other mods, possibly adding a sound chip or joystick ports? I also thought it would be cool to play with the 8255 Intel I/O chip connected to the bus of the ZX81. To control external devices. Just a thought. I have several XT IBM motherboards that use these chips for cassette input and keyboard. Anyway, excellent video.
In principle the ZX81 can address 32KB, but you need to replace the ULA with an FPGA then, and free up one pin to use as address line. The Z80 can do it, the problem is synching up with the ULA.
By the way, I am working on 're-imagining' (i.e. re-designing) of the ZX81. Hopefully I will add an SD-card interface, a joystick port and a PS/2 keyboard. Right now I am trying to re-write the kernel (ROM) to make sure I can do this other stuff. The hardware is easy, the challenge is the kernel.
@@thebyteattic ...Fantastic ideas! Maybe bring some ZX81 fans into the project, let others (say a ZX81 users group) carry the water for you on the ROM rewrite whilst you deal with the other upgrades? Just a thought. I am thinking a step by step approach, for instance start with the joystick port (I understand a couple A/D chips and discreet components are involved), then add PS/2 keyboard interface. I know these elements of the upgrade can be done with the existing ROM as both were offered as an upgrade through various companies without modification to the ZX81. I like where your going with this.
@@thebyteattic Hope this helps with the RAM upgrade to 64KB: www.sinclairzxworld.com/viewtopic.php?t=1734 This fellow came up with a daughter board that seats the ROM and new RAM chips nicely. This fellows ROM was bad, so he did burn a new ROM image, but unmodified from the original apparently. I hope this helps, but hey, your probably satisfied with your very respectable 16KB upgrade, which is much easier and certainly is a boost, making your ZX81 much more usable and productive.
Very interesting! Would it be possible to design a drop-in replacement PCB that uses original chips, and also makes 16K of RAM addressable without the need for bodge wires? I tried searching online but couldn't find any such projects.
I have a faulty ROM on my ZX81; before I buy a new one, I would like to make a test with a EPROM 27C64 (on a breadboard, as wiring is different). Any idea where I can get the ROM content as binary or intel hex file?
I personally find them useless. If you need to know how a signal is behaving, break out the oscilloscope (they aren't expensive anymore either) and you will know.
I don't think it is worth the trouble making an SD card work and changing the ROM etc. This site forum.tlienhard.com/phpBB3/viewtopic.php?f=2&t=3360 shows Wespi running on an ESP32. These come in larger sizes now that will hold every piece of software ever made for the TS1000/ZX81 and a web-based site where you can add more .p files. They will be adding commands to rename, delete, move etc. that are run from the ZX81. All via the SAVE signal that use to tell the TV to make those squiggly lines. I am going to try this out. My only worry is load time. They say it will be the highest available on the Z80, which I think is 1200baud. I hope that is fast. I still don't even like waiting 5 seconds for a program to load, being use to the emulator(s). The genius of this is that you mount it inside the computer and then use any computer to access the website on wifi that's inside the ZX81. It's like having a built in hard drive without the hassle of trying to get IDE interfaces to work. At one point I bought an IDE-->Compact Flash board to try to do this, (seems like noone has actually done this, but I did see a 1581 commodore emulator type unit that might work)
I really learned a lot from watching your excellent videos on the ZX81, thank you for doing them. I finally got my TS1000 working, I replaced the ULA with a vLA81, and that did not cure the problem, then I replaced the Z80 cpu and that cured it. Now it has a new ULA, CPU, and 62256 memory mod. I am going to order in a new keyboard membrane for it. Thanks again for your help. RJ
Nice to hear it!
My TS1000 has a D4016C chip, DIP24, in there with the LK2 already jumpered. I'll be changing to a 62256 this week. I'm glad I watched this video first, one less pin to worry about. Thanks!
Yes I agree, fantastic work. After I finished Pimping Up my ZX81, I decided to do the same on a TS1000 that I have. I did the composite video mod, and got the K cursor just as on the ZX81, next I did the memory upgrade just as before and got the K cursor, only it takes a little longer to appear, next I did the power mod, and installed a new Z80 and again seemed to be OK with the K cursor, and let it sit for awhile to see it anything over heated. I then put on a new keyboard membrane and reassembled it. After reassemble I hooked it up and powered it on, up came the K cursor as before, so I tried out some of the keys, and to my surprise none of the key function at all. I took it apart and checked for +5 volts at all the locations and all seems OK, same for the 0 volts. I am at a loss, any idea what the problem could be? I am thinking the ROM? Any help would be appreciated. Thanks. RJ
Was the previous keyboard membrane working at least partly, before you replaced it?
@@thebyteattic I would have to say no, because it was broken at the connector. I went ahead and done the composite mod and got the K cursor, and the the RAM upgrade. I did cut the broken end off the membrane and tried it, but had no response, so I then installed a new membrane with the same result. Any thoughts?
I did the power mod and Composite mod on mine this week and it works awesome. Crystal clear image.
Fantastic!
Fantastic work! What a joy to have the genesis of your computer experiences back in such beautiful and functional form. Your girlfriend really added a master touch with her work on the badge.
Indeed, better than original in so many ways, the personal touches not least among them!
Thank you!
I’ve designed a little PCB with an SMD 62256 chip on it, together with a decoupling capacitor and a 10K Ohm resistor on it and all the needed routing on the PCB itself, so no need to bend pins. The 10K Ohm resistor is put between pin 28 (+5 volt) and pin 27, it is to make HRG8 mode working. The ZX81 was my first computer too.
Cool. Is it on Github? If so, it would be nice if you could post a link here.
@@thebyteattic I will publish it on github soon. Might even sell them in small batches if these is demand. My first prototype had some errors. These are now fixed.
Muchas gracias, me he entretenido viendo las tres partes de la mejor restauración/actualización de un ZX81 que he visto, tengo un Timex Sinclair TS1000 a la espera de una ULA de reemplazo y un mod. de video, ahora estoy animado a hacerlo. Saludos desde Colombia.
Thank you very much, I've been entertaining myself looking at the three parts of the best restoration / upgrade of a ZX81 that I have seen, I have a Timex Sinclair TS1000 waiting for a replacement ULA and a mod. video, now I am encouraged to do so. Greetings from Colombia.
Thanks! And good luck with your restoration!
Great work! Tnks for share!
Cheers!
Heat would probably loosen the adhesive on the keyboard - just not too hot since you don't want to melt he plastic :P
Can you also do one on repairing the 1016 RAM module.
Also, I found a 128K memotech from a donation store years ago. Still have it, not sure if it was for a TS1000 or TS2068. I think back then I plugged it into a TS1000 and it did a white blank screen. Maybe I even fried that board (ULA), I will be pulling it out of storage soon.
Great video, thank you for making it. I don't understand why the RAM isn't addressing the full 32KB, why only 16KB? I thought the ZX81 could address 64KB directly.
Must have been covered in another video, I will check them all out. I look forward to other mods, possibly adding a sound chip or joystick ports? I also thought it would be cool to play with the 8255 Intel I/O chip connected to the bus of the ZX81. To control external devices. Just a thought. I have several XT IBM motherboards that use these chips for cassette input and keyboard.
Anyway, excellent video.
In principle the ZX81 can address 32KB, but you need to replace the ULA with an FPGA then, and free up one pin to use as address line. The Z80 can do it, the problem is synching up with the ULA.
By the way, I am working on 're-imagining' (i.e. re-designing) of the ZX81. Hopefully I will add an SD-card interface, a joystick port and a PS/2 keyboard. Right now I am trying to re-write the kernel (ROM) to make sure I can do this other stuff. The hardware is easy, the challenge is the kernel.
@@thebyteattic ...Fantastic ideas! Maybe bring some ZX81 fans into the project, let others (say a ZX81 users group) carry the water for you on the ROM rewrite whilst you deal with the other upgrades? Just a thought. I am thinking a step by step approach, for instance start with the joystick port (I understand a couple A/D chips and discreet components are involved), then add PS/2 keyboard interface. I know these elements of the upgrade can be done with the existing ROM as both were offered as an upgrade through various companies without modification to the ZX81.
I like where your going with this.
@@thebyteattic Hope this helps with the RAM upgrade to 64KB:
www.sinclairzxworld.com/viewtopic.php?t=1734
This fellow came up with a daughter board that seats the ROM and new RAM chips nicely. This fellows ROM was bad, so he did burn a new ROM image, but unmodified from the original apparently. I hope this helps, but hey, your probably satisfied with your very respectable 16KB upgrade, which is much easier and certainly is a boost, making your ZX81 much more usable and productive.
@@gregryan7761 Thanks!
Very interesting!
Would it be possible to design a drop-in replacement PCB that uses original chips, and also makes 16K of RAM addressable without the need for bodge wires? I tried searching online but couldn't find any such projects.
Yes, this is not only entirely possible, it's quite straightforward. I am not sure whether anyone has done it, but it should be quite trivial.
@@thebyteattic hint-hint, nudge-nudge... 😉
@@thebyteattic oh oh, and also the composite video mod directly integrated into the PCB in place of RF modulator 😁
I remember when the red faded off my ZX81 case lettering, I painted it back in with liquid paper followed by a red felt-tipped pen! 🤣
I have a faulty ROM on my ZX81; before I buy a new one, I would like to make a test with a EPROM 27C64 (on a breadboard, as wiring is different).
Any idea where I can get the ROM content as binary or intel hex file?
I am not sure they are online somewhere, though I never searched for it.
@@thebyteattic I can't find it neither... Strange, as the ROM is fully disassembled with comments...
A logic probe could be your friend here, they're not expensive.
I personally find them useless. If you need to know how a signal is behaving, break out the oscilloscope (they aren't expensive anymore either) and you will know.
Those badly bent resistors are triggering my OCD. Otherwise great!
Why not get it to use the entire 32k? A lot of people on youtube have done it!
th-cam.com/users/results?search_query=32k+zx81
I don't think it is worth the trouble making an SD card work and changing the ROM etc. This site forum.tlienhard.com/phpBB3/viewtopic.php?f=2&t=3360 shows Wespi running on an ESP32. These come in larger sizes now that will hold every piece of software ever made for the TS1000/ZX81 and a web-based site where you can add more .p files. They will be adding commands to rename, delete, move etc. that are run from the ZX81. All via the SAVE signal that use to tell the TV to make those squiggly lines. I am going to try this out. My only worry is load time. They say it will be the highest available on the Z80, which I think is 1200baud. I hope that is fast. I still don't even like waiting 5 seconds for a program to load, being use to the emulator(s). The genius of this is that you mount it inside the computer and then use any computer to access the website on wifi that's inside the ZX81. It's like having a built in hard drive without the hassle of trying to get IDE interfaces to work. At one point I bought an IDE-->Compact Flash board to try to do this, (seems like noone has actually done this, but I did see a 1581 commodore emulator type unit that might work)