Just done this mod. It's perfect. Thank you. To test the amount of RAM type: PRINT PEEK 16389*256+ PEEK 16388-16384 1k = 1024 16k = 16384 32k = 32768 (just in case someone does a 32K version)
Forty Niner was the only "Hi Res" game on the ZX81 and I used to play it a lot. The game didn't use the normal ZX81 built in graphics but instead used its own custom built graphics coding to allow sprites. It was the work of a machine coding genius. Nowadays anyone that has the skills to programme any computer in machine code / assembly language is regarded as a mystic or god by lowly IT technicians and IT engineers, as they have powers over computers beyond comprehension. If one can programme in assembly language / machine code one understands why Core processors exist and how they work. (Clue: It's to do with not having to stack ALU register contents into memory everytime an interrupt or branch instruction is encountered). What do electronics engineers do when they want a good laugh?? Ask and IT engineer to explain how they think a Core processor operates.....
Thanks for the link, pleased it the upgrade went well. The board in my blog was an issue 3, yours is the issue 1 (there was no issue 2). The diode positioning and numbering is the same, just the resistors by their side are different. You don't need to remove the RAM if you use a RAM pack, when it is plugged in, it disables the onboard RAM chip(s), although you will still only get 16K. The Minstrel ZX80 clones are my design, although based mainly on the original ZX80 design but in the ZX81 form factor.
Thanks for the blog!!! Ah, I see now regards the revisions! And thanks for mentioning that the RAM is disabled by the RAM pack - excellent, will make it much easier to test when I re-cap the RAM pack. What's the difference between ZX80 and 81, can you easily convert the 80 into an 81?
ZX80 has TTL chips rather than the ULA that the ZX81 has. ZX81 also has an NMI mode which allows it to switch off the screen to do some thinking. The ZX80 (and ZX81 in slow mode) spend most of their processing time drawing the screen and only run code at the top and bottom of the screen. You can convert a ZX80 to a ZX81 by adding an NMI circuit, more info on Grant Searle's excellent site: searle.hostei.com/grant/zx80/zx80nmi.html
Just completed the zx81 mem mod today on an issue 3 board. Clearest and cleanest I could find on the internet! Finally got rid of those 16k external nightmare expansion modules after having them some 35+ years in my procession.Thank you very much! (Also thanks to Dave, the link doesn't work anymore by the way).
They used rolls of thin tape for the traces plus scalpel and tweezers. The DIL IC layouts were either strips of pads or sized transfers. All onto acetone film at 1:1 scale or maybe 2:1 Try SCCS Interface and Interface Age for 70s computing.
for those wires that you use you could get a 4 pin fan header connectors to make it easier to remove the chip or to place back in to save the effort in carefully re-soldering
Yes, great idea! I might just use single pin sockets for them and connect them that way or something. I will probably never need to disconnect that new chip though, only reason I did it that way was to make it easy to revert.
I had no idea you could do that.. Suddenly that makes the ZX-81 much more interesting! I'd pretty much discarded it as a platform due to the horrible RAM packs. Very cool indeed, thanks for sharing. :)
Yeah I bet! I need to get someone to fix my ZX-81 now.. I've tons of tapes for it that I never got to play with! Still too scared to play with a soldering iron myself, heh.
Best way to start is by just messing around on some scrap board - something like an old alarm clock or something. Desolder some components, solder some on there, practice removing a chip etc. It's not hard, but its important to practice on something you can destroy first - just to get used to techniques.
HA HA! Timex/Sinclair (here in the USA) RAM WOBBLE! I remember that all too well! Back in the day, somebody sold a metal bracket to screw the RAM Pack to the Sinclair at the bottom of both units! It was sold on the computer magazine ads of "COMPUTE!" Magazine!
The only thing I can think of with regards to the cassette deck interference would be there must be something possibly the main electric feed to your house going under your conservatory, when you put the cassette deck on the ground it sounded to me like classic 50Hz hum, if you had some field probes for your oscilloscope you could pick it up on the scope and could workout where the feed actually is and what direction it is travelling. Oh, great mod by the way. Dave Curran strikes again (top man) and finally, I love how your cat pops into shot every now and then just to say hi. So cute.
Does sound like that, if you have anything that detects live current that would be a start, metal detector? tbh you could pull the cassette deck over the floor to see where its emanating from haha, stop working on the floor its no good for you back anyway :) great video btw
Hehe, yes, I think he's right! I do have a cable detector, I might try that on the floor to see if I can find anything. Chances are though an mains feed will be below quite a depth of concrete I would think.
Mains wiring shouldn't be radiating massively though, as the current will be balanced. It's solid underneath is it, no spaces where some equipment may be?
The ZX81 disables the internal 1k RAM chip when the external pack is fitted, so I expect it would disable a 16or 32k chip in the same position. There is a way to switch the old chip back in; I used it for user-programmed graphics
My neighbour had a speccy. He also had a tiny screw driver that he used to fiddle with the tape head *all the time*. It seemed like such a pain in the nuts compared to the C64 Datasette.
Hehe, sounds like his tape deck needed a repair :P The other funny one similar to that is the PS1 upside down in order to load discs - due to the plastic sled wearing.
May I suggest soldering the wire to a single turned pin and push it on the pin of the chip next time? if you don't like soldering directly to a chip, way less chance of cooking a pin and should be dead easy to do with "helping hands". Great vid. I want another Speccy, maybe a +2 to replace the one that had issues and the wife chucked out, or a rubber key, not sure though, prices are high (for my budget) now, thanks to the retro revolution!
Would of be a good idea to get some electrical varnish and cover the traces. I`m running out of jobs on the Spectrum and like to over engineer things. :)
Great Vid. I used to have 49er for the 81 back in the day. it was always the hardest game to load for some reason. Possibly cos of high res graphics? Football manager had no graphics and loaded every time. maybe a good idea to use that as a test prog in future episodes, :-)
I think you're right! I also had no end of trouble trying to load this particular game as a kid! I wondered if it was to do with the volume of data (needing 16Kb) and the reliability of the RAM pack connectivity for that long load.
First computer I ever used was a Timex Sinclair 1000 - basically a US version of the same computer and it had the same flakiness with the rampack - I remember it being quite frustrating.
GadgetUK164 - Retro Gaming Repairs & Mods yeah it's the same internally except it has a ntsc modulator and 2k of built in memory. The 16k ram pack looks exactly the same it just says Timex on it :).
I honestly don't know. I do have a Timex Sinclair 2068 (basically a US Spectrum) that has an EX-Rom for basic sound routines - it's kind of a cross between a regular spectrum and a 128 model. I've been making videos about it, but I can't quite finish the video because I can't get it to load and I've had the worst time repairing it.
There are some slight differences in the ROM that cause some minor compatibility problems but most software will run unmodified. Biggest difference is the shipping with 2k instead of 1k of ram, and better RF shielding to meet North American requirements. They also made the Timex Sinclair 1500, which was a 1000/ZX-81 with 16KB RAM on board in a silver Spectrum style case with rubber chicklet keyboard.
to someone of your ability those c64 consoles are good for fixing c64's, you can even fit a c64 consloe board into a c64,you have to solder the keyboard connectors and a few other bits, a standard c64 rom is a good idea too, but if you have a broken c64 and a console c64 it is worth considering. get yourself a c64 console and the other c64 boards and put them side by side, i think you will find it very interesting, the console versions are useless unless you have a stack of carts, there used to be a video on youtube where a key board from an sx64 was plugged into a game system along with a tape deck, after turning on it loads a game from tape, it had been up graded to c64 spec, i can't seem to find it now.
Yes, you could do that - but.... The console version of the C64 sells for around £300+, a standard C64 sells for £30... If you find a console version of the C64, dont take the PCB out of it!!! =D
Hello and thank you for your very good video. However, there is something ambiguous about your connections: Have you voluntarily connected A11 of RAM on A12 of ZX and A14 of RAM on A11 of ZX and A12 of RAM at + 5V ?
Apart from the other ideas, the only other one I can think of is perhaps Wifi reflecting off the floor. But I would have thought that far too high a frequency to interact with this old technology. Not that I know about these things.
Nice work there. I did something similar to one of my ZX81's last year. Mine only has 8k at the moment (largest SRAM I had in stock) but I'll up that soon as a suitable SRAM comes available or I bite the bullet and buy one. As well as the RAM upgrade I also fitted a ROM switch so it now boots either Sinclair BASIC or FORTH. Regarding your hum issue, is it more noticeable in your conservatory? I'm wondering if the tape recorder is picking the hum up that is being radiated by the ring main. Do you get the same effect powering the cassette player from batteries? try switching the ring main that runs that room off then power your TV, ZX81 and cassette player from an extension lead and see if the hum is still there. Had lots of fun chasing down similar hum problems back when I was a full time AV engineer.
Thanks! Cool, I didn't know you could run FORTH on these!!! I will try batteries later to see if I can work out whether its the ring main or not! =D Not something I've come across before!
What happens to the original RAM when you connect the RAM expansion? Is it "masked" or does the RAM expansion not enable the lowest 1k or RAM and just complements the original? Thank you in advance.
Hi Chris. Just a ‘slightly’ random question: what model of TV is it you use as it seems ideal for retro projects? Are there any other steps you use in connecting old consoles etc? Cheers, Dave
Thanks! I will check the model number later. It's just a 2008 ish Panasonic 720P / 1080i LCD TV. One of the nice things with the Panasonic models of that particular range is they were of the era that we all started transitioning from standard def to hi def, and so the upscaling was taken seriously, and as a result any old SD signal gives a really nice upscaled image.
I believe you could do that, but I think you need to add a couple of NAND gates to enable the extra 16K block there, and I suspect little software would support it.
Sorry for being 2 years late but I'd like to take a stab at a guess to the source of the interference to the tape player... I think you live above a secret MI6 office. js.
i am finding a lot of 28 pin 32k ram chips that say "62256 family" in their description, does that mean that these can be used as well? or does the chip need to have that exact number on it in order to be compatible with regards to the datasheet/pinout?
GadgetUK164 - Retro Gaming Repairs & Mods just installed one of the chips i managed to buy in my Timex1000 on a nice socket, all dandy, but that 2k NEC D40160 chip i removed to install that socket, could that be used as a drop-in upgrade in a ZX81? i know it would only add 1k, but i'm just curious. also, don't want to throw it away.
Maybe the tape deck is suffering a similar issue to that of land line telephones... when you place your mobile near one? There is a speaker on the cassette deck. An the old magnetic tapes .. so as someone else mentioned in the comments .. possibly your house mains under the floor.. or your neighbours WiFi ..? Or a door way to a parallel universe ..? If things start moving you should contact a priest.. Cute cat dude .
Thanks, and Luigi the cat says thanks too lol =D Things do move around the house, I think I need a priest! Oh wait, that's just my annoying wife moving things...
TBH, not sure - the Z80 has a 16 bit address bus, so it can technically address 64K, but the problem is the ROM sits somewhere in the address range too. And I guess the ULA will likely use some address space probably.
@@GadgetUK164 Im sure i remember seeing 64k ram packs advertised in sinclair user/ programs , they went down the whole length of the 81's back and cost ridiculous amounts of cash :-)
@@GadgetUK164 ULA uses I/O, you just need some logic to not select when the first 8K is output. A15 A14 A13 to a three input NAND gate, any high input gives a low CS output. all low which would be 0-8K gives a high output.
There were some aftermarket keyboards that were pretty good. I was lucky enough to find a Timex/Sinclair 1000 at a thrift store that came in a 3rd party case with a 'real' keyboard: 8littlebits.wordpress.com/category/timexsinclair/ I'll have to do this upgrade on that unit. That would really make it nice.
Dave's blog:- blog.tynemouthsoftware.co.uk/2017/10/zx81-internal-16k-ram-reversible-version.html
I hate to be picky but I've been looking for a 32K upgrade so if you're feeling generous, please post that solution as well.
Just done this mod. It's perfect. Thank you. To test the amount of RAM type:
PRINT PEEK 16389*256+ PEEK 16388-16384
1k = 1024 16k = 16384 32k = 32768 (just in case someone does a 32K version)
Forty Niner was the only "Hi Res" game on the ZX81 and I used to play it a lot.
The game didn't use the normal ZX81 built in graphics but instead used its own custom built graphics coding to allow sprites. It was the work of a machine coding genius.
Nowadays anyone that has the skills to programme any computer in machine code / assembly language is regarded as a mystic or god by lowly IT technicians and IT engineers, as they have powers over computers beyond comprehension.
If one can programme in assembly language / machine code one understands why Core processors exist and how they work. (Clue: It's to do with not having to stack ALU register contents into memory everytime an interrupt or branch instruction is encountered).
What do electronics engineers do when they want a good laugh?? Ask and IT engineer to explain how they think a Core processor operates.....
Your timing with this vid is amazing. Just bought the ram to follow Dave’s blog a few hours back
Haha, thanks - blame Dave, he pointed out to me that he had just done this mod on his blog and I couldn't resist giving it a go.
Thanks for the link, pleased it the upgrade went well. The board in my blog was an issue 3, yours is the issue 1 (there was no issue 2). The diode positioning and numbering is the same, just the resistors by their side are different. You don't need to remove the RAM if you use a RAM pack, when it is plugged in, it disables the onboard RAM chip(s), although you will still only get 16K. The Minstrel ZX80 clones are my design, although based mainly on the original ZX80 design but in the ZX81 form factor.
Thanks for the blog!!! Ah, I see now regards the revisions! And thanks for mentioning that the RAM is disabled by the RAM pack - excellent, will make it much easier to test when I re-cap the RAM pack. What's the difference between ZX80 and 81, can you easily convert the 80 into an 81?
ZX80 has TTL chips rather than the ULA that the ZX81 has. ZX81 also has an NMI mode which allows it to switch off the screen to do some thinking. The ZX80 (and ZX81 in slow mode) spend most of their processing time drawing the screen and only run code at the top and bottom of the screen. You can convert a ZX80 to a ZX81 by adding an NMI circuit, more info on Grant Searle's excellent site: searle.hostei.com/grant/zx80/zx80nmi.html
Awesome, thanks for all the info =D Might have a go one day!
@@GadgetUK164 Anybody who has a mint condition ZX80, leave it original, they are collectors items, good money.
Just completed the zx81 mem mod today on an issue 3 board. Clearest and cleanest I could find on the internet! Finally got rid of those 16k external nightmare expansion modules after having them some 35+ years in my procession.Thank you very much! (Also thanks to Dave, the link doesn't work anymore by the way).
They used rolls of thin tape for the traces plus scalpel and tweezers.
The DIL IC layouts were either strips of pads or sized transfers.
All onto acetone film at 1:1 scale or maybe 2:1
Try SCCS Interface and Interface Age for 70s computing.
The things he does for us!
Nicely done! Very good attention to detail.
Thank you very much!
The hum is from EMI from power lines. On audio that usually exist because one of the audio lines are connected to power earth.
When joining up the address wires, you could cut a short length of header and make a plug
Yes, that's a good idea!
for those wires that you use you could get a 4 pin fan header connectors to make it easier to remove the chip or to place back in to save the effort in carefully re-soldering
Yes, great idea! I might just use single pin sockets for them and connect them that way or something. I will probably never need to disconnect that new chip though, only reason I did it that way was to make it easy to revert.
I had no idea you could do that.. Suddenly that makes the ZX-81 much more interesting! I'd pretty much discarded it as a platform due to the horrible RAM packs.
Very cool indeed, thanks for sharing. :)
Yeah - I had no idea either until Dave pointed me towards his blog! It's certainly much more reliable now.
Yeah I bet! I need to get someone to fix my ZX-81 now.. I've tons of tapes for it that I never got to play with!
Still too scared to play with a soldering iron myself, heh.
Best way to start is by just messing around on some scrap board - something like an old alarm clock or something. Desolder some components, solder some on there, practice removing a chip etc. It's not hard, but its important to practice on something you can destroy first - just to get used to techniques.
Aye, that's good advice.. I'll get around to it eventually, hopefully. :)
HA HA! Timex/Sinclair (here in the USA) RAM WOBBLE! I remember that all too well! Back in the day, somebody sold a metal bracket to screw the RAM Pack to the Sinclair at the bottom of both units! It was sold on the computer magazine ads of "COMPUTE!" Magazine!
The only thing I can think of with regards to the cassette deck interference would be there must be something possibly the main electric feed to your house going under your conservatory, when you put the cassette deck on the ground it sounded to me like classic 50Hz hum, if you had some field probes for your oscilloscope you could pick it up on the scope and could workout where the feed actually is and what direction it is travelling.
Oh, great mod by the way. Dave Curran strikes again (top man) and finally, I love how your cat pops into shot every now and then just to say hi. So cute.
Does sound like that, if you have anything that detects live current that would be a start, metal detector? tbh you could pull the cassette deck over the floor to see where its emanating from haha, stop working on the floor its no good for you back anyway :) great video btw
Thanks =D Cat says thanks too lol! I think you're probably right - that does make sense!
Hehe, yes, I think he's right! I do have a cable detector, I might try that on the floor to see if I can find anything. Chances are though an mains feed will be below quite a depth of concrete I would think.
Mains wiring shouldn't be radiating massively though, as the current will be balanced. It's solid underneath is it, no spaces where some equipment may be?
Matthew Day could be loops of wire?? Sorry Gadget you now have to did your conservatory floor up so we can answer this enigma😂😂
The ZX81 disables the internal 1k RAM chip when the external pack is fitted, so I expect it would disable a 16or 32k chip in the same position. There is a way to switch the old chip back in; I used it for user-programmed graphics
I remember i had a mate with a spectrum and he had to put the tape deck on its side when games didnt load. Ah the querks of early 80s gaming.
My neighbour had a speccy. He also had a tiny screw driver that he used to fiddle with the tape head *all the time*. It seemed like such a pain in the nuts compared to the C64 Datasette.
Haha, yes - I spent a fair bit of time messing with the azimuth to get those hard to load games loading....
Hehe, sounds like his tape deck needed a repair :P The other funny one similar to that is the PS1 upside down in order to load discs - due to the plastic sled wearing.
Thanks for the WD-40 trick!
May I suggest soldering the wire to a single turned pin and push it on the pin of the chip next time? if you don't like soldering directly to a chip, way less chance of cooking a pin and should be dead easy to do with "helping hands". Great vid. I want another Speccy, maybe a +2 to replace the one that had issues and the wife chucked out, or a rubber key, not sure though, prices are high (for my budget) now, thanks to the retro revolution!
Love it =D Nice idea! I will alter that next time I am in there. I wanted to heat shrink those connections too, then it will be nice and tidy.
Yes it would look really nice with heat shrink. Happy to inspire ya Gadge.
Would of be a good idea to get some electrical varnish and cover the traces. I`m running out of jobs on the Spectrum and like to over engineer things. :)
Hehe =D Yes, that's a good idea actually! Either that or UV solder mask paint / nail polish.
Great vid there I have done this mod on 2 of my zeddys. Keep up the good work there gadget😁
Thanks! Much appreciated =D And thanks to Dave Curran at Tynemouth Software for sharing his mod!
Great Vid. I used to have 49er for the 81 back in the day. it was always the hardest game to load for some reason. Possibly cos of high res graphics? Football manager had no graphics and loaded every time. maybe a good idea to use that as a test prog in future episodes, :-)
I think you're right! I also had no end of trouble trying to load this particular game as a kid! I wondered if it was to do with the volume of data (needing 16Kb) and the reliability of the RAM pack connectivity for that long load.
I'm willing to bet that dielectric grease would get that external RAM pack to work MUCH more reliably!
Nice idea lol =D
First computer I ever used was a Timex Sinclair 1000 - basically a US version of the same computer and it had the same flakiness with the rampack - I remember it being quite frustrating.
I didn't know that Timex had a model of this - I might have a look for one of those! =D
GadgetUK164 - Retro Gaming Repairs & Mods yeah it's the same internally except it has a ntsc modulator and 2k of built in memory. The 16k ram pack looks exactly the same it just says Timex on it :).
Cool =D I am guessing the basic ROM is different between the two do you jnow?
I honestly don't know. I do have a Timex Sinclair 2068 (basically a US Spectrum) that has an EX-Rom for basic sound routines - it's kind of a cross between a regular spectrum and a 128 model. I've been making videos about it, but I can't quite finish the video because I can't get it to load and I've had the worst time repairing it.
There are some slight differences in the ROM that cause some minor compatibility problems but most software will run unmodified. Biggest difference is the shipping with 2k instead of 1k of ram, and better RF shielding to meet North American requirements. They also made the Timex Sinclair 1500, which was a 1000/ZX-81 with 16KB RAM on board in a silver Spectrum style case with rubber chicklet keyboard.
to someone of your ability those c64 consoles are good for fixing c64's, you can even fit a c64 consloe board into a c64,you have to solder the keyboard connectors and a few other bits, a standard c64 rom is a good idea too, but if you have a broken c64 and a console c64 it is worth considering.
get yourself a c64 console and the other c64 boards and put them side by side, i think you will find it very interesting, the console versions are useless unless you have a stack of carts, there used to be a video on youtube where a key board from an sx64 was plugged into a game system along with a tape deck, after turning on it loads a game from tape, it had been up graded to c64 spec, i can't seem to find it now.
Yes, you could do that - but.... The console version of the C64 sells for around £300+, a standard C64 sells for £30... If you find a console version of the C64, dont take the PCB out of it!!! =D
really, i remember when dixons were selling them for 14.99.
Wow, wish I had bought a load of them back then lol
Says Ireland on the chips! Awesome :)
Hehe, yes - easy for people to forget that some great electroincs came from Ireland - Seagate may still be over there I'me not sure?!?
Just assembled (bonded) in Ireland though. The actual chip was made in Japan, Taiwan or Korea.
Do you have to join up any of the links? I watched another UA-cam clip and they linked LK1. It was a different revision board though.
I didn't here, but maybe as you say it's beccause its a different board revision!
Hello and thank you for your very good video.
However, there is something ambiguous about your connections:
Have you voluntarily connected A11 of RAM on A12 of ZX and A14 of RAM on A11 of ZX and A12 of RAM at + 5V ?
See this guide - I pretty much did the same mod I think:- blog.tynemouthsoftware.co.uk/2017/10/zx81-internal-16k-ram-reversible-version.html
Apart from the other ideas, the only other one I can think of is perhaps Wifi reflecting off the floor. But I would have thought that far too high a frequency to interact with this old technology. Not that I know about these things.
Would it be simpler to disconnect and pull up pin 8 (^CS) on the 1K chips, without removing them?
Yes, you could do that - you will need to feed the CS with 5v (through say a 4K7 resistor) though.
have you checked your house on the uk Radon maps, its radioactive and you might be above some
Nice work there. I did something similar to one of my ZX81's last year. Mine only has 8k at the moment (largest SRAM I had in stock) but I'll up that soon as a suitable SRAM comes available or I bite the bullet and buy one. As well as the RAM upgrade I also fitted a ROM switch so it now boots either Sinclair BASIC or FORTH. Regarding your hum issue, is it more noticeable in your conservatory? I'm wondering if the tape recorder is picking the hum up that is being radiated by the ring main. Do you get the same effect powering the cassette player from batteries? try switching the ring main that runs that room off then power your TV, ZX81 and cassette player from an extension lead and see if the hum is still there. Had lots of fun chasing down similar hum problems back when I was a full time AV engineer.
Thanks! Cool, I didn't know you could run FORTH on these!!! I will try batteries later to see if I can work out whether its the ring main or not! =D Not something I've come across before!
Amazing Vid, might be some induction going on.
Thanks =D Yeah, I think you're right - suspected mains feed into the house...
What happens to the original RAM when you connect the RAM expansion? Is it "masked" or does the RAM expansion not enable the lowest 1k or RAM and just complements the original? Thank you in advance.
If you do the mod the way I did it, the old RAM gets disabled. The new RAM provides all of the RAM.
Hi Chris. Just a ‘slightly’ random question: what model of TV is it you use as it seems ideal for retro projects? Are there any other steps you use in connecting old consoles etc? Cheers, Dave
Thanks! I will check the model number later. It's just a 2008 ish Panasonic 720P / 1080i LCD TV. One of the nice things with the Panasonic models of that particular range is they were of the era that we all started transitioning from standard def to hi def, and so the upscaling was taken seriously, and as a result any old SD signal gives a really nice upscaled image.
The cassette is acting as a capacitor between the floor and the mains
Why not use the full 32k or would it create q problem.
I believe you could do that, but I think you need to add a couple of NAND gates to enable the extra 16K block there, and I suspect little software would support it.
Sorry for being 2 years late but I'd like to take a stab at a guess to the source of the interference to the tape player... I think you live above a secret MI6 office. js.
LOL =D
That hum is caused by a sneaky cable to a drugs den next door from your meter and you’re paying for it!
Just kidding. :-P
i am finding a lot of 28 pin 32k ram chips that say "62256 family" in their description, does that mean that these can be used as well?
or does the chip need to have that exact number on it in order to be compatible with regards to the datasheet/pinout?
I think it should work - just check the pinout first to make sure its the same, but I think most of those 32K 62256 equivalents have the same pinout.
GadgetUK164 - Retro Gaming Repairs & Mods
thanks! can't wait to try this!
GadgetUK164 - Retro Gaming Repairs & Mods
just installed one of the chips i managed to buy in my Timex1000 on a nice socket, all dandy,
but that 2k NEC D40160 chip i removed to install that socket,
could that be used as a drop-in upgrade in a ZX81?
i know it would only add 1k, but i'm just curious.
also, don't want to throw it away.
Maybe the tape deck is suffering a similar issue to that of land line telephones... when you place your mobile near one? There is a speaker on the cassette deck. An the old magnetic tapes .. so as someone else mentioned in the comments .. possibly your house mains under the floor.. or your neighbours WiFi ..? Or a door way to a parallel universe ..? If things start moving you should contact a priest..
Cute cat dude .
Thanks, and Luigi the cat says thanks too lol =D Things do move around the house, I think I need a priest! Oh wait, that's just my annoying wife moving things...
Is it true that a ZX81 could go up to 64k?
TBH, not sure - the Z80 has a 16 bit address bus, so it can technically address 64K, but the problem is the ROM sits somewhere in the address range too. And I guess the ULA will likely use some address space probably.
@@GadgetUK164 Im sure i remember seeing 64k ram packs advertised in sinclair user/ programs , they went down the whole length of the 81's back and cost ridiculous amounts of cash :-)
@@GadgetUK164 ULA uses I/O, you just need some logic to not select when the first 8K is output. A15 A14 A13 to a three input NAND gate, any high input gives a low CS output. all low which would be 0-8K gives a high output.
hum is AC Hum .. at Ground level some feed back from your mains ground.
Yes, I think you're right! Mains cables run under the conservatory floor - it's probably related.
;-)
that Zx81 kb looks like painful to use
Haha, yes - you are 100% right! It's a nightmare to use!!!
There were some aftermarket keyboards that were pretty good. I was lucky enough to find a Timex/Sinclair 1000 at a thrift store that came in a 3rd party case with a 'real' keyboard: 8littlebits.wordpress.com/category/timexsinclair/
I'll have to do this upgrade on that unit. That would really make it nice.
KITTY!
Hehe =D
Mi viene il mal di mare 🌊 🌊 🌊 cavalletto? 😁
ha ha all i seem to see is your cat walk past the camera LOL she/he likes to not miss out being famous lol
:o)
Radium lol 😅
Yeah, a ground loop I think, but I thought it was funny at the time =D