BBC Master 128 Circuit Schematics (Remastered PDF) Mainboard and keyboard

[Ukwebb]

thanks - fixed now - not sure where that went to !
and updated the edit date on the pdf in the bottom right of the page, and added JAN23 to the filename

[1024MAK]

thanks - fixed now - not sure where that went to !
and updated the edit date on the pdf in the bottom right of the page, and added JAN23 to the filename

Excellent, thank you

Mark

[BeebMaster]

Just noticed that it shows pin 5 of IC13 (LM386) connected to R36 10R which should be R38 10R. Hopefully anyway, as that's how Station 112 is connected up!!

[Ukwebb]

Just noticed that it shows pin 5 of IC13 (LM386) connected to R36 10R which should be R38 10R. Hopefully anyway, as that's how Station 112 is connected up!!

fixed and updated thanks !

[vexorg]

Another small bug in the text. IC30 outputs are "DMA 0","DMA 1","DMA 2","DMA 3" (with a space); and the same lines elsewhere are "DMA0","DMA1","DMA2","DMA3" (no space)

[Ukwebb]

nice spot
Looks to have been wrong in the original too !

fixed and uploaded to the first post

[vexorg]

Was just spotted by chance as hunting down a problem with DMA0 to DMA3 signals.

[arnoldemu]

I was tracing VS I think I've got a correction:

IC40 Pin 2 is labelled as blank but on the MDFS scanned schematics it's pin 3?

[vexorg]

Another small bug, IC11, the 146818 cmos chip, pin 16 should be pin 18

[vanekp]

Transistors Q11 Q13 are PNP transistors in the diagram they are shown as NPN and are connected in reverse (emitter and collector should be swapped around) to what they are in a BBC master.

[Ukwebb]

Hi Peter
Not 100% sure on this one; unless I'm mis-understanding you?

The components Q11 and Q13 on my actual master are as per the schematic BC309's which are indeed PNP transistors, and physically sit just behind the composite video output port.

The Motorola datasheet schematic shows the BC309 as the same drawing as on the master schematic, albeit they are upside down to each other

But in both schematics the arrow is pointing at the junction, not the outer circle as it would be for a NPN transistor

Maybe someone with better electronics knowledge can confirm one way or the other?

[vanekp]

1. the arrow is point out which is indicates a NPN transistor
2.being PNP the emitter cant be connected to 0V it would be revers biased so would never conduct.
3. I have looked in my BBC Master which is how I discovered it was not shown correctly on the circuit diagram when I was helping some on on the forum with a problem with the circuit.
you can find more over this Here

[Ukwebb]

Oh - I was looking at the picture you first posted - which shows it as it should be - ahhhhh!
that wasnt clear ! - i thought you were showing the problem area and describing the problem - not that you've editing it then posted the fixed version!

I'll get that amended asap

[Ukwebb]

IC40 Pin 2 is labelled as blank but on the MDFS scanned schematics it's pin 3?

Another small bug, IC11, the 146818 cmos chip, pin 16 should be pin 18

Transistors Q11 Q13 are PNP transistors in the diagram they are shown as NPN and are connected in reverse (emitter and collector should be swapped around) to what they are in a BBC master.

all done Thanks !
and a bonus of an updated keyboard schematic too

[vexorg]

What cad package do you use?

[Ukwebb]

It's done in Corel Draw currently.
It would be nice to do it in kicad or similar but I wanted to get as close to original as possible. But once this is stable it will give someone a clear design to build it in kicad

[vexorg]

What are the common export options for corel? I suspect it's a pure drawing package that wont be able to go into any kind of schematic/pcb editor.

[Ukwebb]

Correct it's a vector drawing program. As the objective was to reproduce the original drawing sheets.
The information within would be useless to kicad/etc, other than as a clean/correct image reference to work from.
But given that on the schematic some parts are the logic gates with a chip, and others are the chips themselves, and others again are somewhere in-between.... I'm not sure any drawings in any system other than directly in kicad/easycad etc. would be workable.