Sinclair ZX80 / ZX81 / Z88 Forums

I love my ZX80s, and I know that not many were made compared to the Spectrum, ZX81 etc, but there is an endless supply of them for sale over at that famous auction site and there always has been - if anything there are more on sale now than ever (currently there are 11 listed!) 20 years ago it was h...

I just received another batch of 2114 chips. Too many to stick into a RAM pack and test them in sets of six and then figuring out which one failed. Thinking of using an arduino and a bread board to make a small test jig. And then write a sketch that uses different patterns to test the device. Shoul...

Does a ZX80 booting up to BASIC prove the RAM is OK? The reason I ask is because I have a selection of 2114 RAM chips and would like to sort them into "good" and "bin"... there does not appear to be many (cheap, or off the shelf) ways of testing this RAM Obviously if it fails to boot at all, I can d...

They both look fantastic. My ZX80 looks like a Simpsons Special Edition, so I am tempted to do this myself (but like you, slightly wary given some other results I've seen) My main concern however is the longevity. I've seen articles where the yellowing eventually came back, and possibly that it weak...

Update - back to square one, but better than being at square -1! Reflowed all connections, cleaned thoroughly with Isopropyl Alcohol - no change. Removed & checked all logic with my TL866 EPROM programmer's tester - all passed (assuming the logic testing function is accurate.) Tried alternative Z80 ...

Hello Mark, pin 20 looks nothing like compared to the real '80 pin 20 (2).jpg pin 20 (1).jpg Not sure if the clock looks quite the same either. It didn't used to have that little "lower" edge - not sure if that's normal? pin 6 (2).jpg pin 6 (1).jpg I almost had a working clone previously, it's got t...

Just a mini update... gah, my clone now does not display anything at all! Just blank like before (nothing at the video out, plenty of activity around the CPU and other areas, including many of the previously checked ICs, so its not totally dead!)- so it's not an issue with the CPU as previously. non...

@ MaFli - yes the character set appears perfect on the non-inverted characters (at least, to me) If I do a basic PRINT CHR$(N); program to display all the characters, it's only the inverted ones which go crazy. The regular characters are never affected. If I attach the probe lead to the "bottom" leg...

Hi, If I understand you correctly, that measurement comes from the "upper" part, of C11 the side closer to the rear of the case? I am a total scope novice, but took a measurement there: pic_32_3.jpg (When I do this, the text on screen disappears, if I probe the other side, I get a 3.2Mhz square wave...

Hi Mark, you may be right, as I have a further update! I was comparing IC18 between my Real ZX80 and clone; What I've noticed is that if I check pin 9, with the probe grounded to the Modulator, the flicking completely disappears and it all looks normal. I'm pleased to have (hopefully) narrowed it do...