Sinclair ZX80 / ZX81 / Z88 Forums

XavSnap wrote: ↑Thu Aug 13, 2020 8:33 am [edit]
http://www.computinghistory.org.uk/det/ ... ack-GB18U/

Link to Maplin magazines :
https://worldradiohistory.com/Maplin-Electronics.htm

TalkBack_SPO256al2.jpg


Zx81 Talk-Back : Maplin #5
https://worldradiohistory.com/UK/Mapeli ... -03-05.pdf

Have fun.

Thank you for the readable scans!!!!!
That will make things much easier

R7 on my board is 4k7 ohm

Mageco (VTR) SPO256-al2 board:

From:
http://zx81.ordi5.free.fr/vtr/download/ ... ECO%5D.pdf

R7:
YEL-VIO-BLK-BLK-BRN
470x1 qua:1

470 Ohms 1%

Something's wrong in this kind of circuits…
Like "Elletronica mister kit", this article seem to be a rough draft of the original project.

This purpose (article) is clearly sloppy and wrong to sell the greatest number of PCB…

Buy a PCB, and put a bunch of components…
That's all.

XavSnap wrote: ↑Fri Aug 14, 2020 12:32 am R7:

resistor.jpg

YEL-VIO-BLK-BLK-BRN
470x1 qua:1

470 Ohms 1%

I have altered my original post here as I've come to the conclusion that on my board, who ever assembled it has reversed R2 and R7 I shall reverse their position and report back as to whether it works or not.

EDIT.

Have now reversed R2-R7 as per the schematic and can report it all works ok.

"R" is the decimal notation in the BS1852 format.
https://reviseomatic.org/help/e-resisto ... 0Codes.php

R47 = 0R47 = 0.47 Ohm.

47R = 47R0 = 47 Ohm.

470R= 470R0 = 470 Ohm.

XavSnap wrote: ↑Fri Aug 14, 2020 8:16 pm "R" is the decimal notation in the BS1852 format.
https://reviseomatic.org/help/e-resisto ... 0Codes.php

R47 = 0R47 = 0.47 Ohm.

47R = 47R0 = 47 Ohm.

470R= 470R0 = 470 Ohm.

Er yes I know I'm fully aware how to read resistor code,what does that have to do with R2 and R7 being in the wrong place on my board? I assume this is aimed at me?

I am only pointing out that R7 which should be 470 ohm and R2 which should be 4700 ohm seem to have been swapped on my board regardless of terminology.

XavSnap wrote: ↑Fri Aug 14, 2020 8:16 pm "R" is the decimal notation in the BS1852 format.
https://reviseomatic.org/help/e-resisto ... 0Codes.php

R47 = 0R47 = 0.47 Ohm.

47R = 47R0 = 47 Ohm.

470R= 470R0 = 470 Ohm.

Maybe it was for me
It was something I didn't know (at least the R47 one - never run across that notation before)

I'm one of the lucky 10000 who learned something today

Moggy wrote: ↑Fri Aug 14, 2020 1:54 pm I have altered my original post here as I've come to the conclusion that on my board, who ever assembled it has reversed R2 and R7 I shall reverse their position and report back as to whether it works or not.

EDIT.

Have now reversed R2-R7 as per the schematic and can report it all works ok.

Thank you.
It's good to know that the design as written (or with the resistors reversed) works.

When I run into issues I now know it's my implementation rather than a design error.