UK's National Computer Museum Looks For Help Repairing BBC Micros

tresho writes: 1981-era 8-bit BBC Micro computers and peripherals are displayed in a special interactive exhibit at the UK's National Museum of Computing designed to give modern students a taste of programming a vintage machine. Now, the museum is asking for help maintaining them. "We want to find out whether people have got skills out there that can keep the cluster alive as long as we can," said Chris Monk, learning coordinator at the organization.

"Owen Grover, a volunteer at the museum who currently helps maintain the cluster of BBC Micro machines, said they held up well despite being more than 30 years old. The BBC Micro was 'pretty robust,' he said, because it was designed to be used in classrooms. This meant that refurbishing machines for use in the hands-on exhibit was usually fairly straightforward. 'The main problem we need to sort out is the power supply,' he said. 'There are two capacitors that dry out and if we do not replace them they tend to explode and stink the place out. So we change them as a matter of course.'"

Comments

Ah That's Good Shit

[Greyfox]

The first computer I bought for myself was a Vector II graphics machine. It was an odd beast -- integrated computer/video, MFM 10 MB hard drive, some number of kilobytes of RAM, I forget exactly, and most oddly a dual processor machine. It had both an 8086 and a Z80 chip in it and could use either one or the other to run DOS (I want to say 2.0) or CP/M. Mine came installed with CP/M. This was in the early 90's, just before the 286 really started to catch on.

For my hardware class, I brought it in, took it apart and handed the chips around the class. At the end, I reassembled the whole thing and booted it back up. Fun little presentation. That old hardware could really stand up to a lot of abuse.

Re:Ah That's Good Shit

[gsslay]

This was in the early 90's, just before the 286 really started to catch on.

I think your dates may be a bit out. By the early 90s the 286 was vintage.

Ask other retro communities

[Neo-Rio-101]

There is a fairly healthy C64 community, including electronic engineers and tinkerers, who have been able to build replacement power supplies for the good ol' breadbox given that it had particularly ugly power supply issues as well.

I don't think it would be too difficult to ask them to take a look at the BBC Micro to see what could be done there....

Re:Ask other retro communities

[MacTO]

Yes, and replace them with modern power supplies before they fail. Power supplies rarely fail in a clean manner, which is to say that they will still provide power even if it is not functioning properly. The voltage may be too high or too low or, in the case of dried out capacitors, fluctuate. In most cases the computer will behave irratically, yet there are also cases where it can end up damaging other components. So just take the preemptive measure of replacing the power supplies to ensure that the critical components, the ones that are hard to replace, will have a lower chance for failure.

Re:Ask other retro communities

[BasilBrush]

This is the UK, where they'll find more engineers with experience fixing BBC Micros than C64s.

They'll certainly get some education support people that maintained BBC Micros for Local Education Authorities. And they may well even get some ex-Acorn engineers - some of them will be retired now, and would be happy to help a museum out preserving something they love.

BTW, one of the neat things about the BBC Micro is that they shipped with a complete circuit diagram for the main board in the back of the manual.

Re:Ask other retro communities

[LWATCDR]

This is for a cluster that is being used not an exhibit in a glass box.
I think modifying the existing power supplies is probably the best way to go today. Replace the caps and possibly the voltage regulators with newer parts might be a really good way to go today.
I would suggest starting a project to create a modern PS that could be a drop in replacement for the old one. It could use a lot less power and be more reliable in the long run.

Re:Virtulize it

[adnonsense]

Emulators are ten-a-penny, here's one which works in your browser: http://bbc.godbolt.org/ The point of the exhibit is to provide the full tactile 80's microcomputer experience.

Re:Replacing capacitors...

[Bing Tsher E]

Power supply circuit boards of that vintage, and even some of them today, are usually single-sided without plated through vias to pull out.

Not sure if you knew this, or if you're sorta bush league yourself.

Re:Virtulize it

[wonkey_monkey]

Yes, and they could copy the Mona Lisa so everyone could see it up close.

Re:Boooooooooo...

[famebait]

Damn, just when my points expired.
Loved that machine, and can still hear that boot-up sound.

Pity the 64 beat it hands-down on graphics - the BBC was way more advanced on the OS side, and the built in BASIC was actually a decent structured language you could do real stuff in.

I could do this, I used to be a Commodore Service.

[MindPrison]

..technician back in the 80's to 90's.

I can read from the various posts in this thread that you all think it's a walk in the park to fix these old 80's computers, oh boy...you guys may know a couple of common things such as dry soldering and drying capacitors, but there's a lot more to fixing those things than you might know.

One of the most common faults of the 80's was the ROM/RAM circuits, they where often clusters of 2/4/8 kilobyte ram chips (often 4164 etc.), and finding dead ones requires a couple of "old skool tech skills", one of the simplest one is the "thumb test", is one of the Ram chips very hot (you could of course use a bottle of cold-spray, I don't know what it's called in your country...but to us it was just Cold spray, this is essentially a spray that sprays super cool air because of a chemical process when in comes in contact with air, the surface will be really cold, forming ice crystals) and then you can see clearly which surface is getting hot fast. Another method is to use the oscilloscope to see if anything is out of the ordinary (you need to know how it looks as an image first, the voltage changes because of the logic communication will form an image, and if you know how it looks when normal, this is also a method we used.)

You can also use a logic tester, this is an instrument that can monitor the traffic in those logic circuits, you can set it to the speed of the actual logic (usually 1 to 20 MHz, depending on the computers speed) and see if everything is okay.

Another common flaw back then, was broken prints...over some time, these boards gets really hot, and this stretches the metal on the PCBs, and broken connections is some of the hardest things to find.

Another typical flaw is design flaw, over time...we needed to change I/O chips on certain models simply because it was so badly designed that they would eventually go bust, they where very sensitive too...so many of the DIY'ers out there who made their own Fast-Loaders/Robotics connected to the I/O ports would regularly blow these chips.

Pity I live in Scandinavia, I'd love to retire doing this :)