I have been slowly adding to my collection of retro goodies over the last few months, and one of my more recent acquisitions was a cute little ZX81.
My first memory of any interaction with a computer was with one of these back when I was in Primary school. I don't remember being particularly impressed, especially as the keyboard seemed awful to use, and the only programs we had, we had to type in ourselves! (Not particularly engaging for this 7 year old I'm afraid)
Still it was the first computer I had ever seen, and it did have an impact upon me and so is maybe worthy of a second chance.
I picked this up from a work colleague with a big stack of tapes, a spectrum+ and a collection of joysticks and interfaces, no tape deck though. He told me he hadn't fired them up for quite a while, and they had lived in his mum's loft since they disappeared into there back in the 80's.
It was with a small amount of anticipation that I unpacked and fired them up.
The Spectrum+ was absolutely fine and was duly packed back up again until I had time to play with that some more.
The ZX81 was in a bit of a state though. Cosmetically it's not too bad but the RF output is heavily distorted. Bizarrely, the output becomes worse the more I type, this will need some investigating later on.
Unfortunately half the keys were also unresponsive. I knew that it was pretty easy to get hold of replacement membranes so I ordered one and waited for it to flop through my letterbox. It would be something I could be getting on with whilst I tried to find out what was going on with my Video output.
The membrane finally arrived today, so time to get busy.
Removing the RAM pack is a doddle. It is only held on with Velcro after all. This was a Sinclair approved and quite necessary Mod in order to hold any expansion in place!
Next, flip over and remove 5 screws, 3 of which are hidden underneath the rubber feet.
The base pops off nice and easily and you are straight at the bottom of the motherboard, with only 2 more screws to remove,
Carefully pulling the two keyboard ribbons free I flipped the motherboard over to have a look. A simple looking design, but then there isn't much to it.
Obviously, I wasn't the first person to open this and have a play. One of the ribbons had quite a substantial tear across it! Oh well, the rest of it seems ok.
Anyhoo, the new membrane/ keyboard replacement is an almost identical match for the original in appearance and feel. I was a little worried that it would be very obviously a replacement, but you would be hard pressed to tell the difference.
Continuing with the rampant professionalism that is the halmark of this little beauty the keyboard is glued to the plastic casing. It can actually be removed quite easily by careful peeling.
One way to tell the difference between the original and replacement keyboards does require you to remove the keyboard in order to see the most distinguishing mark. A handy manufacturing date. This one was knocked up in 1980, the new ones have 2008 on them.
I had always wondered how these worked, and was intrigued by what it would actually look like. If like me this has been a cause of unbearable curiosity, prepare to be gratified.
Lovely isn't it.
Threading the ribbons through, pressing the new keyboard into place and reattaching them to the motherboard took literally minutes and I had the whole thing back together in less time it takes to make a cuppa. If only all repairs were as simple.
Firing her up and testing the keyboard out reveals that at least the keyboard function is now fully servicable! The Display, however, is still garbage though. I may investigate a composite hack, this has proven to be a vast improvement on my other speccy's but that's for another day.
I thought that maybe it was down to a weak PSU or maybe some bad caps, but testing the voltages on the PSU everything seems fine. I also swapped out the RF cable with one I know to be absolutely fine and made sure there was no power packs or obvious sources of possible interference in the way.
That said, it's been a good start and a simple little machine to work on. I mean 'little' quite literally, these things are much smaller than I remember. But then again, I was quite a bit smaller myself back in 1981.
The only thing I was disappointed with really, is finding out about the tear in the ribbon cable. I had believed my colleague when he said it had been untouched. I could have save myself a tenner by having a look and trimming the ribbon cable instead! According to some of the forums I have visited, this is quite a normal repair option. There is plenty of spare cable after all! Ho Hum, It's quite possible that the old keyboard contacts could have been on their way out anyway.
My first memory of any interaction with a computer was with one of these back when I was in Primary school. I don't remember being particularly impressed, especially as the keyboard seemed awful to use, and the only programs we had, we had to type in ourselves! (Not particularly engaging for this 7 year old I'm afraid)
Still it was the first computer I had ever seen, and it did have an impact upon me and so is maybe worthy of a second chance.
I picked this up from a work colleague with a big stack of tapes, a spectrum+ and a collection of joysticks and interfaces, no tape deck though. He told me he hadn't fired them up for quite a while, and they had lived in his mum's loft since they disappeared into there back in the 80's.
It was with a small amount of anticipation that I unpacked and fired them up.
The Spectrum+ was absolutely fine and was duly packed back up again until I had time to play with that some more.
The ZX81 was in a bit of a state though. Cosmetically it's not too bad but the RF output is heavily distorted. Bizarrely, the output becomes worse the more I type, this will need some investigating later on.
Unfortunately half the keys were also unresponsive. I knew that it was pretty easy to get hold of replacement membranes so I ordered one and waited for it to flop through my letterbox. It would be something I could be getting on with whilst I tried to find out what was going on with my Video output.
The membrane finally arrived today, so time to get busy.
Removing the RAM pack is a doddle. It is only held on with Velcro after all. This was a Sinclair approved and quite necessary Mod in order to hold any expansion in place!
Next, flip over and remove 5 screws, 3 of which are hidden underneath the rubber feet.
The base pops off nice and easily and you are straight at the bottom of the motherboard, with only 2 more screws to remove,
Carefully pulling the two keyboard ribbons free I flipped the motherboard over to have a look. A simple looking design, but then there isn't much to it.
Obviously, I wasn't the first person to open this and have a play. One of the ribbons had quite a substantial tear across it! Oh well, the rest of it seems ok.
Anyhoo, the new membrane/ keyboard replacement is an almost identical match for the original in appearance and feel. I was a little worried that it would be very obviously a replacement, but you would be hard pressed to tell the difference.
Continuing with the rampant professionalism that is the halmark of this little beauty the keyboard is glued to the plastic casing. It can actually be removed quite easily by careful peeling.
One way to tell the difference between the original and replacement keyboards does require you to remove the keyboard in order to see the most distinguishing mark. A handy manufacturing date. This one was knocked up in 1980, the new ones have 2008 on them.
I had always wondered how these worked, and was intrigued by what it would actually look like. If like me this has been a cause of unbearable curiosity, prepare to be gratified.
Lovely isn't it.
Threading the ribbons through, pressing the new keyboard into place and reattaching them to the motherboard took literally minutes and I had the whole thing back together in less time it takes to make a cuppa. If only all repairs were as simple.
Firing her up and testing the keyboard out reveals that at least the keyboard function is now fully servicable! The Display, however, is still garbage though. I may investigate a composite hack, this has proven to be a vast improvement on my other speccy's but that's for another day.
I thought that maybe it was down to a weak PSU or maybe some bad caps, but testing the voltages on the PSU everything seems fine. I also swapped out the RF cable with one I know to be absolutely fine and made sure there was no power packs or obvious sources of possible interference in the way.
That said, it's been a good start and a simple little machine to work on. I mean 'little' quite literally, these things are much smaller than I remember. But then again, I was quite a bit smaller myself back in 1981.
The only thing I was disappointed with really, is finding out about the tear in the ribbon cable. I had believed my colleague when he said it had been untouched. I could have save myself a tenner by having a look and trimming the ribbon cable instead! According to some of the forums I have visited, this is quite a normal repair option. There is plenty of spare cable after all! Ho Hum, It's quite possible that the old keyboard contacts could have been on their way out anyway.