Sinclair ZX80 / ZX81 / Z88 Forums

I have a ZX81 that I built into a Dell PC keyboard, I cut out the numeric keypad and mounted the 81 board there + internal 32K ram. Main part of the keyboard has been re-wired in ZX81 format, works well

Cheers,

Phill.

Which switched mode reg did you use? Would be interested to try this in one of my 80/81 Machines.

Cheers,

Phill.

Right firstly I feel a total idiot :( I've got it working now, the problem turned out to be that I'd somehow forgotten to solder the WR line on the CPU socket to the board :( :( I guess I didn't spot it because the pads on the board and the pins on the socket fit pretty well and on visual inspection...

So that seems that the system looks o.k. and cpu is running it's program. Yes, I'd come to the conclusion that the CPU was running, though the odd thing is I'm not getting any strobing on /IORQ, just /MEMRQ (and /RD & /WR of course). Did you check the two jumpers on J97 (NMI connector) for the vide...

Please follow advices in chapter "Initial startup", page 25 of manual. Cheers. I did look, several times but kept missing the part with the actual info :( What is exactly the problem ? Please use either ZX80 ROM in ROM switch position 4 or 5 or the ZX81 ROM in position 6. A scope would be a good he...

Hi All, I've just finished building my ZX80 Core kit, V1.1 board with IO LEDS and on board video circuit. I'm using the supplied 62256RAM and 28C256 ROM, rom switch is in position 0. But I'm getting no picture. Couple of questions Which way should J100 be connected Left or Right ? Which way should J...

I take it you have already been here http://www.jupiter-ace.co.uk/ace_hardware.html Yep I posted a message on their forums about this too :) And here http://nocash.emubase.de/zx.htm (scroll down to "Hardware Specs"). (yes I know it just looks like ZX stuff...). And here http://searle.hostei.com/gra...

Hi all, Does anyone know of the existence of a set of good quality Jupiter Ace schematics that have the correct connections on. All the ones on the net seem to be based on the Ace 4000 or not to have the pin numbers on the chips. I'm trying to repair an original board and the schematics I can find d...

Right I now have a CPU clock having changed R7 for a 4K7, now to make it work :) Looks like the machine is running but I'm having video sync problems, I've tried running through a USB video capture device and through an LCD TV via a SCART adapter. The USB capture device has a screen full of pixel li...

Ok, doing some reading on common emitter transistor switches I think the problem is that the signal being applied to the base is too great to ever allow Q2 to switch off. I think the solution to this is to alter the value of R7, I'll do some experements this evening and post my results here. Cheers....