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

Discussions about Sinclair ZX80 and ZX81 Hardware
TEEGEE
Posts: 1
Joined: Sat Nov 06, 2021 7:02 pm

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

Post by TEEGEE »

Hello

My zx81 Keybord

sandwich

LASER TRANSPARENT
PAPER
3D PRINT
SWITCH
PCB
Attachments
PAPER.jpg
KB_3D_PRINT.jpg
Laser_transparent.jpg
KYZX81.jpg
PCB_switch.jpg
Franck78
Posts: 12
Joined: Mon Mar 08, 2021 11:24 am

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

Post by Franck78 »

@mahjongg

Hello,

maybe you know, maybe not, but KiCad 5 accept a tilde to put a negate bar on any word (label & comment)

nRD => ~RD

In comments you have to explicitly mark the word to negate.

The ~RD~ signal is blah blah

In V6, it changed. It's now something with ${}, have to explore it.

I'm curious where did you get the ULA functions.
Andy Rea base ?
jojo
Posts: 160
Joined: Mon Mar 16, 2020 5:25 pm

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

Post by jojo »

C1-C2 4.7 pf critical ( as i only have 5pf available ) .


someone can advise ?
Zx81-16k exp.- Spectrum 48 - Spectrum 128- Interface 1 - DIVide - Zx flashcard- Zx printer - Ram turbo-Velleman interface system-Currah microspeech -Ql - 512k exp.- Ql printer - Cst floppy interf.- Double 3.5 floppy- Minerva - Qimi-and much more .
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Paul
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Location: Germanys west end

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

Post by Paul »

Capacitors normally are exact with 10 or even 20 percent tolerance.
So 5pF should do the job
In theory, there is no difference between theory and practice. But, in practice, there is.
jojo
Posts: 160
Joined: Mon Mar 16, 2020 5:25 pm

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

Post by jojo »

another question ,

where are JP3 and JP7 ?

did i miss something
Zx81-16k exp.- Spectrum 48 - Spectrum 128- Interface 1 - DIVide - Zx flashcard- Zx printer - Ram turbo-Velleman interface system-Currah microspeech -Ql - 512k exp.- Ql printer - Cst floppy interf.- Double 3.5 floppy- Minerva - Qimi-and much more .
jojo
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Joined: Mon Mar 16, 2020 5:25 pm

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

Post by jojo »

will there be a problem using bat85 diodes as a replacement for the bat 46 ( hard to find )
Zx81-16k exp.- Spectrum 48 - Spectrum 128- Interface 1 - DIVide - Zx flashcard- Zx printer - Ram turbo-Velleman interface system-Currah microspeech -Ql - 512k exp.- Ql printer - Cst floppy interf.- Double 3.5 floppy- Minerva - Qimi-and much more .
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1024MAK
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Location: Looking forward to summer in Somerset, UK...

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

Post by 1024MAK »

jojo wrote: Thu Dec 09, 2021 8:49 pm will there be a problem using bat85 diodes as a replacement for the bat 46 ( hard to find )
I don’t see a problem with using a BAT85 in 5V circuitry, various other BAT4x diodes can also be used.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Autumn is here. Bye bye summer 2024...
jojo
Posts: 160
Joined: Mon Mar 16, 2020 5:25 pm

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

Post by jojo »

Hi forum , help needed with my zx81+38

have a working unit ( white screen and black cursor ) , but the cursor is NOT a K .

the clone responds to keyboard activity ( every key-stroke gives extra info on the screen ) , but on screen is the same problem as the cursor ( it is only stripes no text ) .

ntsc and pal give the same image .
32k /16k also same result

What did i do wrong ??
m_IMG_1839.jpg
m_IMG_1842.jpg
m_IMG_1840.jpg
update ;

if you wait 10-15 seconds after switching on the screen-image changes from 2 black rectangles to 3 rectangles and stays that way for hours
m_IMG_1852.jpg
Zx81-16k exp.- Spectrum 48 - Spectrum 128- Interface 1 - DIVide - Zx flashcard- Zx printer - Ram turbo-Velleman interface system-Currah microspeech -Ql - 512k exp.- Ql printer - Cst floppy interf.- Double 3.5 floppy- Minerva - Qimi-and much more .
jojo
Posts: 160
Joined: Mon Mar 16, 2020 5:25 pm

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

Post by jojo »

hi forum ,

i found several pictures of build clones with a cat28c256 on it , but
how did you guys manage to get an cat28c256 working on this board ??

i know there is a track to be cut ( as indicated on the pcb ) , but what else needs to be done ?
patch wire 27 to 1 , but what about j10 ?? as indicated in the readme files

any help welcome
Zx81-16k exp.- Spectrum 48 - Spectrum 128- Interface 1 - DIVide - Zx flashcard- Zx printer - Ram turbo-Velleman interface system-Currah microspeech -Ql - 512k exp.- Ql printer - Cst floppy interf.- Double 3.5 floppy- Minerva - Qimi-and much more .
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1024MAK
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Location: Looking forward to summer in Somerset, UK...

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

Post by 1024MAK »

jojo wrote: Tue Dec 28, 2021 2:04 pm Hi forum , help needed with my zx81+38

have a working unit ( white screen and black cursor ) , but the cursor is NOT a K .
That’s most likely a problem with the pixel shift register U9, the connection to it, or the logic that feeds it/controls it. Or it may be U28 or U29. Also check U7 and U4.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Autumn is here. Bye bye summer 2024...
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