BBC Master 128: The evolved 8-bit computer from Acorn

In the basement today we have quite a rare machine (for North America:) The BBC Master 128. It's an evolution of the original Acorn BBC Micro from 1981. My first task is to service the PSU and convert it to 120v, then see if this machine is working.

Part 1: This part!

0:00 Intro
21:10 PSU service, conversion to 120V
41:38 First power up of the computer

--- Video Links

My old video showing off the two BBC Micro machines I brought back from the UK:

BBC Micro PSU repair and 120v conversion:

BBC Master:

65C12 datasheet:

Performing a CMOS reset on the BBC Master:

Adrian's Digital Basement Merch store:

Adrian's Digital Basement ][ (Second Channel)

Support the channel on Patreon:

-- Tools

Deoxit D5:

O-Ring Pick Set: (I use these to lift chips off boards)

Elenco Electronics LP-560 Logic Probe:

Hakko FR301 Desoldering Iron:

Rigol DS1054Z Four Channel Oscilloscope:

Head Worn Magnifying Goggles / Dual Lens Flip-In Head Magnifier:

TL866II Plus Chip Tester and EPROM programmer: (The MiniPro)

TS100 Soldering Iron:

EEVBlog 121GW Multimeter:

DSLogic Basic Logic Analyzer:

Magnetic Screw Holder:

Universal ZIP sockets: (clones, used on my ZIF-64 test machine)

RetroTink 2X Upconverter: (to hook up something like a C64 to HDMI)

Plato (Clone) Side Cutters: (order five)

Heat Sinks:

Little squeezy bottles: (available elsewhere too)

--- Links

My GitHub repository:

Commodore Computer Club / Vancouver, WA – Portland, OR – PDX Commodore Users Group

--- Instructional videos

My video on damage-free chip removal:

--- Music

Intro music and other tracks by:
Nathan Divino
@itsnathandivino

[adriansdigitalbasement]

George who sent me this machine told me that it was indeed used inside the BBC studios, hence the "brand" on the top cover and stickers on the underside. Also, Pete Sapwell (adn some other folks) commented this on the PSU situation:

Hi Adrian, you’re correct about the voltage doubler for the 110V mod on the PSU, the two smithing caps are in series for 240V with the middle unconnected, and if powered on 240V each cap would have 120V across it. When you fit the 110V wire link mains neutral is connected to the centre connection of the caps, the the normal bridge rectifier action charges one on the positive cycle and the other on the negative, again resulting with 110V across each cap and being in series presents 220V to the power supply switcher. :) hope this helps

[cowasakiElectronics]

I was an acorn component level service engineer. Acorn gave out the schematics with the advanced user guide so everyone could see what everything did. Econet was a file system and could be used for loading and saving or printing and acorn sold a server that sat on the network with the other devices. The analogue socket was for analogue joysticks or paddles. Rs423 is TTL RS232 so basically compatible but minus the 10v or whatever 232 was supposed to be. All BBC model A and B computers boards had space and holes for Econet and the disc system but you just had to install the floppy components and a floppy filing system ROM to use it.

[Zerbey]

I owe my entire career to the wonderful BBC Micro, including the BBC Master. I think many IT professionals who grew up in the 1980s and early 1990s do, every school had at least one and they were absolutely fantastic machines.

[adriansdigitalbasement]

George confirmed that this machine was used at BBC Broadcasting House as part of the studio infrastructure! So, there is some real pedigree here to this particular specimen!

Also, thanks to many good tips from patrons, I now know how to service the keyboard on this machine. Watch for part 2, coming soon!

[jimmoores]

The deal with the battery is that the battery sized slot next to the speaker was originally for a rechargeable 4.5V lithium cell, but there was a mistake with the charging circuit which caused it to catch fire/explode. They quickly swapped it out for the shrink-wrapped three AA duracells down the side of the keyboard and a (rather essential) diode in the pack to stop the charging circuit from pushing current through them. The 1MHz bus wasn't for slow peripherals, but rather fast ones like a hard drive - they had a larger amount of address space mapped to them than e.g. the user port. The analogue in is for a multi-channel analogue joysticks/crap mouse/experiments.

[aw]

A Raspberry Pi CoProcessor kit will upgrade the Beeb to the max. The BBC Micro was originally designed to be a multi processor machine with a TUBE interface to connect external coprocessors. Back in the day 3MHz and 4MHz 6502s, Z80, 68000 and x86 coprocessors were available. The coprocessor ran programs and sent API calls over the TUBE to the host machine. Acorn used this feature to develop the original ARM-1 CPU. Using software adapted from the 1985 vintage ARM Development System the Beeb and Master can be upgraded with a modern ARM on a RaspberryPi. As the Beeb was designed to be a multi processor machine which could be upgraded with faster coprocessors adding the Pi upgrades the machine as Acorn historically intended.

[UpLateGeek]

I bet whoever used this machine at the BBC back in the day would be blown away by how much computers run a modern TV studio (assuming they haven't worked in the industry or been retired for a while). We're building a new studio at work and pretty much everything runs off an Ethernet fabric network. There's no huge vision router with hundreds of video inputs and outputs, the network carries all the audio & video to/from the cameras, monitors, and everything else. It has two 400Gbps backbones, with switching capacity over 25Tbps (yes, that's terabits per-second) for each spine switch. The video streams are multicast, and the "video switching" of the streams is done in software (it's basically a software-defined network).

Oh yeah, and the cameras are robotic and fully remote controlled entirely by software. The camera operator can sit it the control room and can move any of the cameras pretty much anywhere on set using a joystick. They can program their camera moves, and it will repeat the exact same move perfectly for take after take. For a single host news program, they don't even need camera operators. They just program the camera moves in the first recording, then as long as every broadcast sticks to the same format, no camera operator needed. They don't need a vision switcher or graphics operator, because the switching between the talent, graphics, and rolling clips is pre-programmed into the rundown. The lighting is all pre-programmed and also robotic, so no lighting director. You can basically run an entire live news show with 4 people, including the talent. Of course, if you're doing interviews or have multiple anchors or a weather presenter, or anything that might need manual camera switching, you'll probably need more crew than that.

So yeah, things have definitely changed a lot in the relatively short time I've been in the industry, let alone since this computer would have been used at the BBC. Thankfully as a network engineer, my job is pretty safe. Software can't troubleshoot and fix a faulty network cable or dirty fibre!

[tom_]

George was extremely kind to send you such an awesome parcel - a rare computer, a ton of jello and some mugs?! What an amazing guy!

[kodabar]

The 'Network 23' writing is interesting. The BBC Master came out in 1986. In 1985, Max Headroom first appeared - and did so on British television. Yes, Max Headroom appeared in the UK first. Now it wasn't a BBC production - it was Channel 4 (there were four channels in the UK at that time). In the initial film (the TV series followed a few days later) Edison Carter crashes into a barrier marked "Max. Headroom 2.3 metres" and the TV network he worked for was Network 23. So I have to wonder if the writing is a reference to that. It may simply have been a reference to the machine's position on the Econet network, but the timing is right.

I used to have "Welcome to Network 23" as my Windows startup sound as well as various Max Headroom noises for all the other system sounds. I also had Network 23 wallpaper and a screensaver. My friends and I would amuse ourselves making these things.

I guess we'll never know if this is a Max Headroom reference, but I've never seen any BBC asset tags like that Television Network sticker.

[andyjdhurley]

This is bringing back lovely memories for me. The BBC B was my 3rd computer which my mum bought for me when my Dragon 32 died within warranty and could not be replaced as the company had gone under. The shop gave us a credit which we used plus extra from mum (a teacher) to get a BBC B on the condition that I used my programming skills to write maths quizzes for her classroom. I was very glad to do this and ended up going in to her school and sorting out all their computers and training the other teachers (they had the machines but no support provided). As a result I came across a few Masters but the 'B's were far more common, I can safely say the Masters ran my code a LOT faster but without any issues at all.

[aw]

The best 8-bit machine ever built in my opinion. It even shares a name with a character from Dr Who.

[sparthir]

More BBC computer videos would be awesome. They are such an interesting machine. The BASIC was one of the best 8-bit ones ever made. And the history is fascinating. They were really well made machines with incredible architecture for the time.

[GavinLyonsCreates]

I had Model B, with Z80 second processor, CUB monitor, AMX mouse and AMX Art, 16 expansion ROM board with Spreadsheet, Wordprocessor, Speller, speech synthesiser, twin floppy drives. It was our family computer for years it was maxed out, it eventually wore out. Great machine, most kids in Ireland at the time had the ZX Spectrum, VIC20, C64. I had Dragon 64 too and used an Oric 1 at some point in school (quite a sad machine that!). My friend had a Tandy TRS 80 with tapes didn't enjoy that machine as I was spoiled with the Beeb with 30 games on floppy. Chuckie Egg, Danger UXB, Zalaga, Elite... so much fun and so many fights with my sister over whose turn to play!

[Psychlist]

Trivia: "arm" used to mean Acorn RISC Machine as you mentioned, but they eventually changed that to another meaning, and then in 2018 made it so their name wasn't an acronym at all anymore. That's also when they changed their branding. That's why they've asked us (Microsoft, but applies to everyone) to write "Arm" and "Arm64" instead of "ARM" and "ARM64" when talking about processors and architecture. They still have old stock out there (especially microcontrollers) with the older branding, but that will eventually go away.

[stevesmusic]

At my school in NZ, when I was 15 we had 10 of them econetted together. One machine had a 20megabte Winchester hard drive attached to it. Another had a floppy drive. That was the machine I always used, so I could play Acornsoft games.

[kpanic]

Hey Adrian, I already commented about how dual input voltage PSUs work on your Mac plus repair video two weeks ago :D
You almost nailed it!


"In case anyone wonders how these dual supply voltage switch mode power supplies work:
They're basically 220-240V power supplies, only the big charge capacitor on the primary side is replaced with two capacitors in series. On 230V everything works as normal, the mains AC is rectified and goes to the capacitors.
If you switch the power supply to 120V (either with an external switch or, like in this case, with a wire link), the center point of the two capacitors gets connected directly to the AC supply, before the rectifier. That way you turn the full bridge rectifier into two half-wave rectifiers, basically creating a voltage doubler circuit: the positive half wave of the input AC charges one capacitor with a positive voltage, the negative half wave charges the other one with a negative voltage (referenced to the center point). That way you get two capacitors charged to roughly 170VDC, which in series is equal to the roughly 340VDC you would get when rectifying 230VAC.
It's simple, elegant and quite ingenious!"

[maxeaves]

I used to do Tech Support at BBC White City at TVC. These machines were used in studios for basic graphics as well as countdown clocks. They were also used in preparing pages in Ceefax.

[timvickerstaff]

I completed my A Level Design Technology on my schools only BBC Master. A couple of years later my teacher called me to say they were having a clear out and did I want the computer? 30-something years later I still have it.

[leeshepherd]

The finest 8 bit machine ever produced IMHO.

[Focusstturbo]

The UK, 1987. A BBC Micro B and a BBC Master in the library of my Secondary School. Serial cables, five and a quarter inch disk drives and playing Mr Do at lunchtimes. Great memories, thank you for making this video.