Sinclair ZX80 / ZX81 / Z88 Forums

aah, work over, time to play again. :) I decided to test the ICs. As the ROM seemed to be a definite gonner, there was no point keeping the elaborate hat on the Z80 (which is a shame, as that's what attracted me to it), so off it came. I put the working ROM and ULA back into the working board, along...

The 7805 should only produce only 5v or near enough not a mixture of 5v and 12v. I didn't twig - that's the input. My UK700 9V PSU is putting out 12V! :shock: edit: Now using a 9V power adapter, which I usually use with my speccys, with the inverter switched for the plug from the UK700. That won't ...

I bit the bullet and opened up my other issue 1 board, which definitely works, and I don't think I damaged the keyboard membrane while doing so. Fingers crossed... It has the same ULA version, and a standard Z80 without the math mod, so I swapped over the 550 ROM to test that on it's own. No K. As i...

I suspect I'm the new custodian of this zeddy. :P 20240409_231557~2.jpg so far, I've disconnected the 16k ram, and put in a known-good 1k, and I've added a zigg.net composite mod. output is blank white, sometimes a moving black and white pattern. the power connection is verry dodgy, so my next plan ...

I've now done the zigg composite mod on my porch-less ZX, and it works! I really wasn't expecting it to, especially as I had no 56R resistors, and used a 47+10 instead, and my last veroboard circuit smoked a resistor, somehow. I think that might've been a duff resistor, but it shook my confidence. :...

The ULA you have does generate the back porch signal. This one does, but my other ZX81 is less fortunate, which is why I also bought parts for a mod that adds a back porch. I keep calling it a ZX8-CCB, but it's not - it's a design from zigg.net Thanks for the extra advice, msknight. I hadn't consid...

aah. it's never simple is it? :) in that case, i'll switch the mod for the 220R resistor and keep my fingers crossed. if that fails, I've ordered parts to build a ZX8-CCB that are still in the post. edit: The 220R mod worked! Extra handy, as I already have lumacode on one of my Speccys, my MSX, and ...

I've already checked the compatibility list , and set the CPLD to Analogue YUV, and done a composite mod, but i did the one with a 2N3904 and a 100R . I've never heard of doing it with just a 220R before. I had the rgbtohdmi set to zx81 composite. I guess i could try the 220R version, but I'm not ke...

Hi! ZX81 #2 arrived today; a series 3 with all the fixed bits. 20240404_211940.jpg As i have nothing that can decode an RF signal, my first job was to do the transistor composite mod. Then I gave it a go... First, i tried it with my tiny car monitor, which has a composite input. I just got a white s...

It's so shiny.. I've never seen such a clean mobo! I'll have to do a video out mod, but i don't think i want to do the RAM and 2450 mods anymore. I'll get a RAM pack, instead!