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Re: I started on my new ZX-81 replacement board (kit) ZX81+38
Posted: Sat Nov 06, 2021 8:54 pm
by TEEGEE
Hello
My zx81 Keybord
sandwich
LASER TRANSPARENT
PAPER
3D PRINT
SWITCH
PCB
Re: I started on my new ZX-81 replacement board (kit) ZX81+38
Posted: Sun Nov 28, 2021 12:38 am
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 ?
Re: I started on my new ZX-81 replacement board (kit) ZX81+38
Posted: Thu Dec 09, 2021 2:38 pm
by jojo
C1-C2 4.7 pf critical ( as i only have 5pf available ) .
someone can advise ?
Re: I started on my new ZX-81 replacement board (kit) ZX81+38
Posted: Thu Dec 09, 2021 5:08 pm
by Paul
Capacitors normally are exact with 10 or even 20 percent tolerance.
So 5pF should do the job
Re: I started on my new ZX-81 replacement board (kit) ZX81+38
Posted: Thu Dec 09, 2021 7:42 pm
by jojo
another question ,
where are JP3 and JP7 ?
did i miss something
Re: I started on my new ZX-81 replacement board (kit) ZX81+38
Posted: Thu Dec 09, 2021 8:49 pm
by jojo
will there be a problem using bat85 diodes as a replacement for the bat 46 ( hard to find )
Re: I started on my new ZX-81 replacement board (kit) ZX81+38
Posted: Fri Dec 10, 2021 12:58 pm
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
Re: I started on my new ZX-81 replacement board (kit) ZX81+38
Posted: Tue Dec 28, 2021 2:04 pm
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 ??
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
Re: I started on my new ZX-81 replacement board (kit) ZX81+38
Posted: Wed Dec 29, 2021 8:22 am
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
Re: I started on my new ZX-81 replacement board (kit) ZX81+38
Posted: Wed Dec 29, 2021 9:48 pm
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