Not quite 8-bit: Acorn A4000 refurbishment

Any 8bit repairs, images, cool things, upgrades etc.
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stephen_usher
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Not quite 8-bit: Acorn A4000 refurbishment

Post by stephen_usher » Sat Mar 09, 2019 5:10 pm

OK, not quite 8 bit, more 32 bit really, but a part of another fine 80s micro lineage...

I've been working recently getting an Acorn A4000 (Archimedes) back up and running after a nasty case of NiCd battery leakage and a dead hard disk (which I actually thought was a power supply problem, but I'll get to that later).

The machine was given to me over 10 years ago by a friend who was clearing out his house. If I hadn't taken it then it would have been skipped!

At the time it was in full working order and came with a very useful Microvitec slow-scan VGA monitor. At the time I had no space down stairs and no Archimedes software, so it went up into the loft. The monitor was used now and again with the Amiga A1200 I bought and renovated a while later. If I knew then what I know know I'd have cut out the NiCd battery there and then and saved the motherboard from some damage.

A couple of years ago I thought I'd take another look at the machine. After all there were Gotek devices which would allow me to use ADF images of software from the 'Net so as to install software. Having heard about the battery issue I opened it up and got a shock. It was a bit nasty in there. So I cut out the battery and cleaned up as best I could. I then plugged it in and turned on. The drive started spinning up and then about 5 seconds later there was a loud *POP* and the power went off. Turning off and on via the power switch showed no life. Given its age I thought it must be a PSU capacitor. I couldn't be bothered to look any further so put it back up into the loft.

A few weeks ago, after someone asked if they could borrow the mouse for a video they were doing, I decided to take a look at the machine again. After all if it were only a capacitor in the PSU that could be fixed. Unfortunately I had quite a few things I had to do so it wasn't until just over a week ago I got the time to bring the machine down.

Thinking that the PSU was probably the main issue I took it out and opened it up. Everything looked good. No popped capacitors. I did a quick voltage check on the 12V and 5V lines and everything looked sound. I put it back in and plugged everything together and still nothing. I was puzzled!

I did another check and the voltages seemed fine, so plugged things back in. This time I forgot to plug the Molex connector into the hard disk though. When I pressed the power button the machine sprung to life! Checking the hard disk, it had a dead short on the 12V line and this was causing the PSU short protection to kick in.
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Having found the major fault I decided to check out the battery area...
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It still had a little dormant corrosion to clean up and the cut off legs of the battery needed removing. I decided that I'd not replace it with another soldered in rechargable but instead fit a coin cell and make it easily disconnected for storage.

It took quite a bit of cleaning before I could install the new connection pins and I was a bit worried about one track on the board. Thankfully the only via/pad which had disintegrated from corrosion was an alternative for the battery so it wasn't required. I then built a little board with the CR2032 cell holder, diode and resister and attached it on the board with some double-sided foam tape.
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Success! (well, other than managing to somehow blow the soldered in 2 amp keyboard fuse when knocking the keyboard on the floor.)

Still, I needed to replace the hard disk. Unfortunately the stock IDE interface and OS drivers for RiscOS 3.11 can only handle hard disks up to 512MB in size. Not only this but I didn't have the hard drive formatting software. I could download a disk images for the RiscOS utilities but as it's a special format I wouldn't be able to actually write it to a floppy disk.

Thankfully I had a pre-LBA IDE disk, an old 10MB drive rescued from a 2000 vintage iMac which would do the hardware job, if I could format it in the correct manner first.

So, how could I get around the formatting problem? How could I get software onto it afterwards?

The Raspberry Pi rides to the rescue!!!

Thankfully there is a port of the latest RiscOS to the Raspberry Pi, so I loaded this onto a 2GB SD card, slammed it into my Pi Model B and away I went. Having a network connected RiscOS machine (albeit a very slow one) meant that I could download the software I needed to get going as well as formatting the hard disk in the special manner people had discovered when using IDE/CF adapters.
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I was away! I had a working machine.

Yesterday the Gotek unit running "FlashFloppy" arrived from AmigaKit and I fitted it. I had to use an old PC floppy cable as the Gotek is rather shorter than a real floppy drive and the original cable wasn't long enough. The only issue was that until a lot of Googling had been done that the FlashFloppy configuration need to be set to "ibmpc" rather than "shugart". This caused a bit of head scratching before I got that working.

Having found a resource for the ADF files necessary, I can at last play games... :D
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Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.

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Icky
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Re: Not quite 8-bit: Acorn A4000 refurbishment

Post by Icky » Sat Mar 09, 2019 7:41 pm

:goodpost:

Storing these old machines in the loft with a battery in is one of the biggest problems. I had a similar issue with an Amiga 500 that had an RTC card in it.

Hard drives are also a pain when they fail. Shorting 12V is not good. Am surprised it didn't take anything else out with it.

stephen_usher
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Location: Oxford, UK.
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Re: Not quite 8-bit: Acorn A4000 refurbishment

Post by stephen_usher » Sat Mar 09, 2019 9:33 pm

Icky wrote:
Sat Mar 09, 2019 7:41 pm
:goodpost:

Storing these old machines in the loft with a battery in is one of the biggest problems. I had a similar issue with an Amiga 500 that had an RTC card in it.

Hard drives are also a pain when they fail. Shorting 12V is not good. Am surprised it didn't take anything else out with it.
I was amazed that it didn't take out the power supply. Acorn obviously thought about their power supplies and designed them well.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.

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DrF
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Re: Not quite 8-bit: Acorn A4000 refurbishment

Post by DrF » Sun Mar 10, 2019 9:27 am

Always wondered about these machines and why they never really took off, yet when I looked deeper they had some big name games released on them so there must have been enough out there to develop for them. I saved I think it was a A7000 from a skip years ago, sadly had to sell it at the time :(

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