Sinclair ZX80 / ZX81 / Z88 Forums

Thank You all, Regarding the video signal, I did some tests a few weeks ago, see https://sinclairzxworld.com/viewtopic.php?f=7&t=4306 After that post I connected my 'oscilloscope' again and got a much better image. I think I,m going to change the composite electronics with one with a 555 timer, then...

I still can't get my old ZX81 to work. I think the problem is with my monitor's composite video input, but I don't have another one to try. Meanwhile I plugged my Z80 into another Z80 computer and it works. My ULA also gives a signal, but it is still the type without a back porch. To make sure it's ...

Yes I mean 7805 and I have access to a multimeter (and a ' scope' ;) ) And my ULA is indeed a version without back porch. My next step is testing my ROM (it seems possible to test a rom with an Arduino) I have ordered a simple Z80 board ( https://www.budgetronics.eu/nl/bouwpakketten/z80-retrocompute...

Thanks Marc, After my ZX81 came a Spectrum, followed by a QL. So my ZX81 has been stored for a very long time and I wanted to get it working again. The keyboard flat cables fell apart, but replacing a keyboard seems not that difficult. Because some capacitors, in the RF box, looked rather weird. I d...

Hello, To be able to use my ZX81 again, I connected the collector of a BC547B to 5v, the base to pin 16 of the ULA and the emitter to the composite video output and to ground via a 100 Ohm resistor. I did not put a resistor between the emitter and composite video out. IMG_0150.jpg IMG_0158.jpg But I...

Thank you Mark

My first "computer" was a Texas Instruments calculator that you could program in up to 50 steps. Then I soldered and Mk14 together and programmed it in machine code. It took me 3 months to write a program that calculated my bio-rhythm. But running the program took barely half a second. I then regula...