Sinclair ZX80 / ZX81 / Z88 Forums

Well... I do just as well as Poland (and even better: with tin plating of the tracks), in my kitchen...

Not wanting to be rude but frankly, for double-sided PCBs of this basic quality, you don't really need a manufacturer.

Instead of loading the ULA with a 2K resistor to the ground (which might not even be enough and will only make the ULA heating more), you can put a diode in series with the base of the transistor (i.e. pin 16, diode, base resistor, transistor base), this way you will lower the level of the signal to...

Using this extremely simplified schematic, you will get a much too strong video signal, which will saturate the video input of your TV set both for the white and the black levels; back porch or not, this can't properly work, but perhaps with an already partly damaged ULA providing a much too weak si...

PokeMon wrote:There is by the way another feature, you can easily invert the video signal with a jumper or even use a switch. Try that with your single transistor.

Don't dare me !

Note that the transistor speed doesn't change a thing about the noise, but if you use a "generic" (BC547 & Co) transistor, its Ton/Toff, and most important, Ts are simply too large (up to 500ns for Ts with a BC547 against 20ns for a ZTX313 or 2N2369A), which will cause trailing effects on white to ...

Well - it depends on the quality of TV/monitor you use to display. A 46" Sony LCD TV for me. And yes, you mileage may vary depending on your TV. I was not happy with the transistor solutions and regardless of the speed of transistor and filter you do - this is not noise from the power supply this i...

With the 210E ULA, which provides already a back porch, you do not need any such circuit... Well - the circuit does more than just add a backporch. It removes the "shit" (noisy white background) that comes out of the ULA and can not be removed with a simple transistor emitter follower (which repeat...

I have a few ZX81s, three are V3 motherboards and work perfectly with the CCB board. My fourth will tune into a 22" flat screen Phillips TV giving a fuzzy but recognisable cursor. When I added the ZX8 CCB I get the same image as Balfords Fairly sharp cursor but about 4 or 5 characters wide. No amou...

I was not totally satisfied with v1: three gates were left unused, and it did not have a way to shadow the ROM with the RAM (there was already the two banks EPROM feature, but erasing the EPROM and reprogramming it each time you want to test some new ROM code is rather tedious)... Well, here is v2.0...

The Memotech HRG is much more complex, using (by remapping) the ZX81 internal 1K RAM so to "patch" the ROM with its own HRG routines. It however doesn't include any RAM expansion like your card does. I'd suspect that the EPROM (if not yet totally erased because of the lack of any protection on its U...