Sinclair ZX80 / ZX81 / Z88 Forums

Thank you for the offer, that's very kind :) I'll persevere with it for the moment as I feel it's something very small, and I'll kick myself once I find the issue :) I might take you up on it in the new year if I haven't gotten anywhere by then. I've tried a number of CPU's (both CMOS and NMOS) BTW....

Thanks, made the measurements tonight and will try and grab some time with the schematic tomorrow or over the weekend to see what's out of place. For reference, here's what I got: pin 2 ic15 IC1 pin 6 1.46k pin 10 24k pin 11 1k pin 17 11k pin 22 4.27k pin 24 11k pin 25 11k pin 26 22k pin 29 3.94k pi...

Thanks for the advice PokeMon! Luckily everything on the board is socketed. Removing the Z80 results in a nice reset signal with a rise time of about 0.5 secs. Through a process of elimination I've worked out that removing IC15 allows the reset signal to be produced normally with the Z80 in place. I...

Hey folks, Having some problems building the ZX80Core and thought I might find some help here. Upon power on, the /RESET line never goes about 1.4V - not enough to release the Z80 from reset. The VCC end of R21 measures 5V exactly, other end at 1.4V. The system clock (6.5/3.25MHz) is running fine, n...