Sinclair ZX80 / ZX81 / Z88 Forums

Quick and dirty snapshots of both of them. Timebase is set different on each, but you get the picture (pun intended )

Maybe the C11 is not the problem, but looking at the schematic this part is where normal/inverted characters are generated. And looking at the TV snapshots on the previous page, this seems to be the problem. Just to make sure, only inverted characters come out wrong? Normal characters remain the sam...

Incidentally, the ZX81 that I was looking at earlier today had two 2114LC-1 fitted. My ZX80 has one 2114LC (IC3) and one 2114LC-1 (IC4). Mark Yup, same here! Just realised my 2114's are soldered in my ZX80... But the ones in my RAM pack are socketed. I could use those and test/swap these in my ZX80...

Indeed, that is the only reason that I can think of, the requirement for the RAM to be fast enough for the video/refresh access. In order to keep costs low, a slower chip was permissible for the other data bits. That's why some instructions say it's okay to fit the faster chips in both positions. I...

Hi Zeddex, Had a quick look at the schematics and pin 9 IC 18 drives part of the video circuits. There's an C-R after this pin that drives the input of IC11-2 and IC16-11. Do you have the correct values installed? 47pF and 470 ohm? I suspect that probing this point adds a bit of capacitance and caus...

Yep, definitely alive! Even works with the ZX80 RAM pack clone. Last post for today

As my late father used to say "Now there's a thing of service". :D :-) Well said! And it is alive! Haven't hooked it up to a screen yet, but I can see a composite signal! Probed around a bit and everything looks okay. Weird thing is it's only drawing 275mA while my original one draws well over 400m...

The fun has begun...

And I just noticed the RS logo on the 74LS138. Weird Never knew RS Components had their own 'brand' of logic devices. And no date code either. Fascinating...

A very nice expansion, extra credits for time-appropriate chips! Thanks! Actually got my original version today! And I am still surprised about the markings on the chips. Each 1K of RAM consists of 2 of these chips. One for the high nibble, the other for the low nibble. But why is one half done wit...