Sinclair ZX80 / ZX81 / Z88 Forums

The latest version (the one uploaded to GitHub) has exactly those jumpers, on the bottom side, so you can still change them even after soldering in a ROM socket. And yes, one of the jumping options is to use the old original ROM, the default is to use a modern OTP, in 8 and 16K variations.

Finalized the PCB https://revspace.nl/images/9/95/Final_ZX81plus38_PCB_rev_1%2C4_top_view.PNG also uploaded production files to github: https://github.com/mahjongg2/ZX81plus38/tree/master/LICENSE.md more pictures here: https://revspace.nl/ZX81plus38_simple_to_build_ZX-81_clone#March_26.2C_ZX-81plus3...

It will look like this: https://revspace.nl/images/7/7a/ZX81%2B35_keyboard_top.png just with some superfluous stuff removed (reset button and LED's). I also designed a keyboard overlay. Here you can see a prototype, together with my older ZX-81 clone, built from SMT components. https://revspace.nl/i...

And this is how the PCB will look like:


Next up, ordering the PCB's (ZX81+38 and keyboard PCB) and testing it.

Finished the last two remaining signals, and applied copper fills. Next is to tweak solder mask and silk screen:

Almost finished, only nBUSACK and nWAIT have not yet been routed to the expansion port. The layout is now quite "busy".
Next week I will attempt to do the two missing connections.

I have made 100% all connections. The expansion port is not fully wired, but enough for I / O devices such as the printer, and programmable sound generators and the like. I'm going to add ground planes on both sides. https://revspace.nl/images/8/82/Finished_layout_ZX81%2B38_19_feb_2020_without_coppe...

The layout is coming along nicely, here is a preview, the white lines (ratsnest) are the connections I have yet to make:

It seems the patch schematic is drawn wrong, the emitter should be on the 150 Ohm resistor side: The emitter can never be on the V+ side, unless the transistor is a PNP, but a ZTX313 is an NPN device. Here is a corrected schematic, also drawn in a more conventional way, with ground at the bottom. Fr...

did a preliminary placement of the components, here is a preview: https://revspace.nl/images/7/73/ZX81%2B38_component_overview_proposal.png its a (very) tight fit, there is hardly any space four routing, and I probably have to optimise the placement (component and port swapping) a lot to get the nec...