ZX81 Adventures!

g'day internet welcome back to another video lately I've had a little bit of an itch that needed a scratch and that itch was the zx81 and I'm not implying that the zx81 is some kind of skin irritation I'm not sure why um the zx81 is a very simple computer there's no arguments about that and it's kind of a machine that a lot of people love but does tend to get lost behind its bigger brother the ZX Spectrum I have always had mixed feelings about the little 81 and it's mainly got to do I think with the fact that the Spectrum was quite the Step Up from this little guy so I did what any normal person would do and that's to jump on eBay find a zx81 pay too much for it and here it is um but when it showed up and it's written on the back and it was actually in the photos on the eBay ad uh zx81 USA uh and I've seen a few of these actually in Australia um and what it essentially means is that this is a ntsc model uh the Ula is putting out 60 instead of 50 hertz and it has a channel Flex switch underneath now from what I'm reading uh the Ula can actually do both so in normal Ula there's literally one pin it's pin 22 and if it's tied to ground through a resistor it's 60 and if it's left open it runs at the normal 50. and one of the channels I can't remember which one off the top my head uh that this either so channel two or three is actually very very close to one of the normal Power channels but regardless of that it's still RF and I'd like to at least get a composite video signal out of this so uh as any normal person would do once they do have a zx81 I jumped on ZX renew and ordered a bunch of stuff and here is that box of stuff so this is what Peter sent me we've actually got three different uh composite mods uh here um this is the one here that we're probably going to use so if you're not aware with the zx81 yes you can pull composite out of it with just a simple mod but it lacks a part of the normal composite signal called the back porch and all three of these modulators reintroduce that back porch in order to get a good composite signal of all of these I'm not going to be able to use this one which is actually got the RCA plug on it and that's because on the USA model they blocked up the normal hole used a different RF modulator and it points out at a different position so as you can imagine if I was to take this and that went in here that's not going to work but I might have a use for this for a future um Sinclair project you'll have to just keep your eye out for that so you know subscribe to the Channel all that kind of stuff uh this is a tiny SMD version of this I believe um I might use this if this doesn't kind of pan out but that'll be something interesting to play with later on uh he also sent me a uh 16k memory upgrade kit so we will probably be putting that together later on in the video uh and underneath all of that is a couple of replacement membranes because I don't know if this works uh I have actually had this thing apart see uh-huh um and the edges of this uh so the ribbon cables that come out they don't seem too bad so we'll try this one first before going to the effort of replacing it but it's always good to have some spares and if you've never heard of ZX renew here's Peter's business card not sponsored just a happy customer and with that strip down here is the internals of our little zx81 like I said it's a pretty simple computer there's not much to it essentially you have a processor ROM uh some RAM and this is the Ula that does 90 of the computery bit of it and what I mentioned before about uh the 50 and 60 hertz it's R30 which is just down here and all we really need to do is just remove that resistor and this will start doing a power signal but the bulk of the work we're going to be doing today is here under the under the RF modulated so I'm going to start by simply removing the RF modulator now I'm not going to deny it removing RF modulators is probably one of my least fun exercises but in this case it needs to be done so let's just get start by some fresh solder oh [Music] got it so what I was intending on doing is fitting this little board inside the RF modulator but it doesn't fit and I'm not sure what I'm going to do about it it's not by much it's maybe a couple of mil but I can't even see a couple of mil worth of excess PCB I could sand off I mean there's not much to this thing but okay I started looking at an idea to try and fit this but then I realized wait a minute I have the tiny one let's use the tiny one which is going to fit so um what I want to do next is get this off I want to get the actual guts of this RF modulator out all right after a good amount of swearing so if we take a closer look at this little guy we need uh so that's a video out that obviously goes to the RCA connector on the RF Cage we need 5 volt in uh ground and Video in so I think first job is to put some wires onto this little board so the original RF modulator actually had this little bit of cardboard in there um and I don't really see any reason why I can't just adhere that to there now watch me instantly regret uh using heavy duty double-sided mounting tape this early in the process even if it moves around it's not going to touch anything awesome all right what I should be able to do is uh I popped the little plastic doohickey out of this and I should just be able to feed the wires through those holes but I want to do it in the right order okay so the logical order seems to be ground video 5 volts and that all should kind of sit in here um oh pull the video out through his wires are way too long by the way don't make my mistake this should just go back in together like that um and yeah there we go that looks like pretty neat well neat for me at least all right next job is to Simply hook up this video out wire to that pin on the RCA so if we take a look at the board we've like I said we need to pull three signals uh ground five volt and video so ground we can just simply pick up from just here that one there that says fr3 um video I believe is this one that says UK 2 and 5 volt um I actually think comes from this guy here that says usa2 but I might run a multimeter across it because that doesn't make any sense because this says UK one and goes to here oh wait usa3 so that is probably the 5 volt there so that's in um before we go and plug like you know put it all back in the case or anything let's test it right up uh composite lead in nine volts let's see what happens hey it like works I I look I've had some a lot of failures lately so the fact this works is awesome now I just want to have a look at and switch to another input this is coming through as power or ntsc it should be coming through his ntsc ntsc right so I need to remove that R30 resistor actually I'm just going to chop it out and in theory this should now come up as pal okay it's not actually telling me pal nice all right let's see if this keyboard Works print oh it does okay it looks like it does at least um cool now as great as this is having a composite mod on it as it currently stands it has 1K of ram now the 16k ram expansion that Peter sent me I am going to use for a future project but in the process of ordering parts for this I also ordered this this is an internal 16k Ram expansion which given I'm never going to want to run this you know without 16k um I think this might be a neater solution for this particular machine the first thing I need to do is there's a jumper here L1 L2 it's currently soldered for L1 and that's what most will be and I need to move the link pin to L2 this isn't as easy as it looks because the bloody um because the holes are right next to right have I got it maybe right probably could have just used a cylinder Bridge right next there's uh three wires that comes provided and we need to solder them to the three pads on this little board all right so as a bit of an explanation what I'm doing the three wires coming off here are labeled a11 a12 and a13 and they get soldered to the top so these diodes sitting down here are diodes one through to eight and so a11 goes to the top of D1 a12 goes to the top of D3 and a13 goes to the top of D5 that should be it I hope I just want to start a little test program to see if the ram expansion works and I don't have a one key I just don't looks like I'm replacing that keyboard so the question is is this going to be one that's just going to nicely come off for me or is it going to put up a fight um I do have tools to fight it with mind you I do have a heat gun like any kind of sticker the hardest part is getting the edge oh okay I'm off remarkably easy uh and left all its adhesive behind that's not going to be fun well that's not a job I'd like to repeat again in a hurry but in the end some Terps got it all the adhesive off now I've just got to get the backing tape off the new keyboard right I essentially have one go at this feed those through and nice and straight why'd the battery die right the most important bit okay new keyboard is on let's see if I actually it actually works now all right it is the next day I'm wearing my uh public holiday flanny um and the new keyboard is in do I have a one key I have a one key so we at least know that's working so with the documentation of the ram upgrade there is a little test program which is what I was tried to type before so let's see how we go all right print Peak one six three eight eight uh where's Plus two five six times Peak one six three eight nine right by right this should come back with thirty two thousand something thirty two thousand seven hundred and sixty eight and there we go 32 768 our 16k Ram expansion is working I'm now going to go and tidy up the disaster that is my workbench and we'll be back in a minute so if I was to be brutally honest with you the main reason I wanted to do this and with the ram expansion it's to play 3d monster maze on the original computer so I've busted out my little svi Cass and it should just be a case of load quote quote enter play and I'll go enjoy my coffee for 15 minutes and there we go sometime later we finally get 3d monster Maze and I suppose the upshot of that internal Ram expansion is I don't have to worry about rampack wobble so there's a plus all right let's see how we go whoops I think I just turned around right ah that didn't take long funnily enough I actually had a really bad habit back in the day in Counter-Strike without fail if I got to a T intersection and the bad guy was on the right and there was a safe on the left I would turn right without fail every time really doesn't take long for him to find you no that's a dead end footsteps are approaching he's seen me did I get out of there in time no ah there you go now it's not all just about 3d monster maze Believe It or Not uh down is actually one of my favorite games that I first found on the Commodore pet and just recently I realized I found that there's a version for the zx81 which I'm kind of like because both the pet and the zx31 I love the Simplicity and I love what people do like this with the Simplicity of such a let's be honest rudimentary computer so now that I've finally worked out what the keys are it's enter is input and O and P is left and right and that's pretty much it I think some of the Collision detection is a little average but this is so cool I love this game come on damn shitty keyboard and it just gets faster and faster ah I keep losing where o and P are on the keyboard but that is such a cool game and there we go the mighty little zx81 it's an awesome little machine I've really come to like it um I'll put a link in the description to Revival Studios page if you want to have a look at this down game I was really kind of pleased to discover it um I didn't know it was available for the zx81 like I said I discovered it on the pet so that's kind of cool but we've managed to get through quite a lot in this video uh We've replaced the RF modulator so we've got nice clean crisp composite video replace the keyboard more at a necessity than anything else we've switched this USA model from 60 hertz to 50 hertz and we installed that 16k memory expansion with all the bits and Bobs going on I hope I can edit this video into something that actually makes sense but for now that will pretty much do it if you like the video click like subscribe or the usual YouTubey stuff as always a massive shout out to my patrons who are scrolling up the screen as I speak and if you'd like to help out the channel there is a link in the description but until then I'll see you in the next one

Channel: Mr Lurch's Things

Views: 47,948

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Id: iqtOFtKxTro

Length: 21min 4sec (1264 seconds)

Published: Tue May 30 2023