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

[Ukwebb]

As an admirer of the work of dv8 with the remastered pdf manuals, the only thing missing was the circuit diagrams.

As a result I decided to do my bit towards this preservation task and started to redraw the Circuit/Schematic Diagrams.

So as a first presentation, I give you the BBC Master 128 Diagram, completely re-drawn, Hi-res, full size (A0) PDF.

I've already started work on the BBC Micro version and I'll add that to this post as soon as I have it completed.

Printed out onto A3 or better still A2, these plans look super clean compared to any scans out there.

Although I've checked the drawings many times, if anyone notices any errors please let me know and I'll correct them.

Enjoy !

Update :24/04/24 - I've also added the BBC Master Keyboard schematic now which I've also corrected and colour coded to make it easier to see each trace


BBC Master 128 Circuit Schematic (latest update 24/04/2024)

Log of corrections completed:
26/05/2021 22:20 : corrected CO to CQ and Added A5/A6 ( missing from original ) on ICs 17/18/23/26
26/05/2021 22:36 : corrected L1 value to 33μH
27/05/2021 12:50 : correct C40 and C43 to 4n7
07/07/2021 : changed crystal near C86 on page 1 to X2
13/08/2022 : Pin 7 of IC49 changed to GD / Pin 2 of IC4 changed to "Q1" / couple of capitalisation errors fixed
09/01/2023 : Fixed missing RW track
23/08/2023 : corrected R36 to R38 / fixed searchable text layer
10/09/2023 : corrected SC1/SC0 labels on IC10 ( should have been SC1&2)
04/01/2024 : corrected DMA 0,1,2,3 to remove space
24/04/2024: corrections: IC40-Pin2>3 'BLANK', IC11 pin 16>18, Q11 & Q13 Graphic to PNP rather than NPN - added Keyboard Schematic

[IanS]

Looks incredible, well done.

I haven't checked the original, but was curious why the A5/A6 pins are not labelled on the RAM (IC17/18/23/26). Aren't the data pins D0-D3, rather than all D0?

[Ukwebb]

Looks incredible, well done.

I haven't checked the original, but was curious why the A5/A6 pins are not labelled on the RAM (IC17/18/23/26). Aren't the data pins D0-D3, rather than all D0?

Thats a very good question - I dont know.

[IanS]

Ah, the data pins should be labelled DQ, not D0.

[Ukwebb]

Ah, the data pins should be labelled DQ, not D0.

on which chip ? --

edit : forget that - I see now ! I'll edit that now !

[KarateEd]

Just wondering if you're following the Copywrite and asked Acorn first.......

[Multiwizard]

I just saw it on FB,, nice work...


Greetings, Wim...

[Ukwebb]

thankyou

[dp11]

C40 and C43 should be 4.7nf caps.

[DaveLecky]

Great work, a fantastic resource...

[TobyLobster]

Nice. See also my circuit diagram for the BBC B https://tobylobster.github.io/mos/mos/S-s25.html

[Ukwebb]

C40 and C43 should be 4.7nf caps.

thanks - fixed

[Ukwebb]

Nice. See also my circuit diagram for the BBC B https://tobylobster.github.io/mos/mos/S-s25.html

Nice work -
nice site too

[retroclinic]

Both brilliant, well done.

Can either of you do a recreation now of the B+ and Compact schematics? The only ones available (that I know of) are really bad quality, these are the ones we could really do with having a good version of!

Thanks, Mark.

[arg]

Nice. See also my circuit diagram for the BBC B https://tobylobster.github.io/mos/mos/S-s25.html

Do you have the resources to produce variants for the different PCB issues (I'm not quite sure which issue yours is).

I have a dyeline print of Issue 3 BBC, though it's faded to almost unreadable having been stuck on the wall for some years. Notable differences are the Econet clock/terminator deleted from your version (empty space top right-hand corner), R172 (suppressing the audio buzz from the 1MHz bus connector), and minor changes around the printer port (the latter crudely drawn on this print - but obviously on the master from which the print was taken rather than my annotation; I think these were changes done as rework on earlier PCBs, maybe reworked on iss2 and rolled in to iss3, or maybe this print was meant to show how iss3 came out of the factory with rework done).

[TobyLobster]

Do you have the resources to produce variants for the different PCB issues (I'm not quite sure which issue yours is).

I don't, I only have the one diagram, which has no issue marked, but I would assume is Issue 7.

[marcelaj1]

Very useful and as it's a PDF you can text search it.
Spotted page 1 top right hand corner, 16MHz crystal should be X2.

Ashley.

[Ukwebb]

Very useful and as it's a PDF you can text search it.
Spotted page 1 top right hand corner, 16MHz crystal should be X2.

Ashley.

Thanks and amended

[nicolagiacobbe]

Wonderful. Thanks for the effort, it is gorgeous.

[Ukwebb]

Wonderful. Thanks for the effort, it is gorgeous.

thankyou

[whizadree]

I've just came by the original 80s blue prints my self , They are Huge and are a pair, ill get a few more images later ,
they came direct from some who worked in Cambridge in the early 80s

[Ukwebb]

oh wow ! theyre awesome ! you're very lucky !!
they belong in a museum! somewhere like TNMOC

[baz4096]

I’d love a print of these!

What a great find

[whizadree]

I Actually could help with prints I have a Professional A3 printer , if you would like one i could see what the best wat to capture them , the only thing is the question of copyright , is there any one here that knows about reproduction info regarding Acorn stuff ,

[baz4096]

I think whilst the copyright probably still belongs to someone, nobody seems to be asserting it recently. I seem to see a lot of “if you’re the copyright holder, please contact me and I’ll stop” around the Acorn themed stuff.

[lushprojects]

Although I've checked the drawings many times, if anyone notices any errors please let me know and I'll correct them.

Thanks so much for this. It really helped me out today.

I did spot a tiny mislabel on Pin 2 of IC4 (should be "Q1")... well actually I personally think it should be Q0 but that's a whole other discussion

[benk]

I’d love a print of these! Make some Great Wall art

[davidmc]

This is beautiful, thanks for drawing this.

One minor detail I noticed is that Pin 7 of IC49 (the uPD7002 ADC) should also be GD, same as pin 5. You have it as G0 (g-zero). Have checked this against an old scanned master schematic, and also the uPD7002 datasheet (https://www.farnell.com/datasheets/100687.pdf)

Aside: Acorn have implemented this (drawn and I buzzed it out on an actual master) with pin 5 and 7 open, yet the datasheet suggests shorting them with an O-shaped trace around pin 6 and the capacitor leg.

[Ukwebb]

Davidmc and lushprojects - :sorry its taken a while but your noted errors have now been corrected and uploaded to the original post

Many thanks for reporting them

Richard

[1024MAK]

Hi Richard,

Nice work

On my PDF viewer, the R/W circuit under the processor (IC14) from pin 34 is incomplete. It should connect to various places including TP6, IC20 pin 31, etc. Can you have a look at this please.

Also, I understand that you may not want to show a drawing version number on the drawing itself. But it would be helpful if you include a version number in the filename. Maybe in hex? That way, it will be obvious in future when your drawing spreads across the internet, which version is which... Saves confusion when someone asks for help when repairing their machine

Mark