Search found 170 matches

by mahjongg
Thu Mar 26, 2020 4:35 pm
Forum: Hardware
Topic: I started on my new ZX-81 replacement board (kit) ZX81+38
Replies: 24
Views: 13132

Re: I started on my new ZX-81 replacement board (kit) ZX81+38

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...
by mahjongg
Thu Mar 12, 2020 1:51 pm
Forum: Hardware
Topic: I started on my new ZX-81 replacement board (kit) ZX81+38
Replies: 24
Views: 13132

Re: I started on my new ZX-81 replacement board (kit) ZX81+38

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...
by mahjongg
Wed Mar 11, 2020 11:54 am
Forum: Hardware
Topic: I started on my new ZX-81 replacement board (kit) ZX81+38
Replies: 24
Views: 13132

Re: I started on my new ZX-81 replacement board (kit) ZX81+38

And this is how the PCB will look like:
Image

Next up, ordering the PCB's (ZX81+38 and keyboard PCB) and testing it.
by mahjongg
Wed Mar 04, 2020 11:36 am
Forum: Hardware
Topic: I started on my new ZX-81 replacement board (kit) ZX81+38
Replies: 24
Views: 13132

Re: I started on my new ZX-81 replacement board (kit) ZX81+38

Finished the last two remaining signals, and applied copper fills. Next is to tweak solder mask and silk screen:
Image
by mahjongg
Wed Feb 26, 2020 11:56 am
Forum: Hardware
Topic: I started on my new ZX-81 replacement board (kit) ZX81+38
Replies: 24
Views: 13132

Re: I started on my new ZX-81 replacement board (kit) ZX81+38

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

Image
by mahjongg
Wed Feb 19, 2020 12:29 pm
Forum: Hardware
Topic: I started on my new ZX-81 replacement board (kit) ZX81+38
Replies: 24
Views: 13132

Re: I started on my new ZX-81 replacement board (kit) ZX81+38

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...
by mahjongg
Thu Jan 30, 2020 2:46 pm
Forum: Hardware
Topic: I started on my new ZX-81 replacement board (kit) ZX81+38
Replies: 24
Views: 13132

Re: I started on my new ZX-81 replacement board (kit) ZX81+38

The layout is coming along nicely, here is a preview, the white lines (ratsnest) are the connections I have yet to make:
Image
by mahjongg
Mon Nov 25, 2019 12:55 pm
Forum: Hardware
Topic: French ZX81, mod on video out before the modulator
Replies: 6
Views: 828

Re: French ZX81, mod on video out before the modulator

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...
by mahjongg
Wed Oct 30, 2019 3:19 am
Forum: Hardware
Topic: I started on my new ZX-81 replacement board (kit) ZX81+38
Replies: 24
Views: 13132

Re: I started on my new ZX-81 replacement board (kit) ZX81+38

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...
by mahjongg
Thu Oct 24, 2019 2:37 pm
Forum: Hardware
Topic: 16K RAM Pack photos
Replies: 9
Views: 3345

Re: JRS 16K RAM Pack

I wondered that too, for a second, when I saw it, then I realized Its probably used to generate the -5Volt from the Raw +9V supply by running it as an oscillator, then driving a diode doubler circuit to invert it to -9V and using a 5V1 Zener to smooth and regulate it. You can see the components to d...