Author Topic: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000  (Read 23022 times)

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Online EEVblog

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Dave tears down and attempts repair on a 1989 vintage Acorn Archimedes A3000 Computer, using the very first ARM processor, the Acorn RISC ARM v2

Service manual: http://acorn.chriswhy.co.uk/docs/Acorn/Manuals/Acorn_A3000SM.pdf
Reference Manual: http://acorn.chriswhy.co.uk/docs/Acorn/Manuals/Acorn_A3000TRM.pdf
Schematics: http://acorn.chriswhy.co.uk/docs/Acorn/Manuals/Acorn_A3000TRM_drawings.zip

 

Offline Zad

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #1 on: August 15, 2013, 12:12:30 am »
It looks like that battery is the achilles heel of the Archimedes. There is this one going on Ebay UK at the moment, and this is what the battery looks like:



www.ebay.co.uk/itm/Acorn-Archimedes-A3000-/161083181402

Yeah... Definitely heading in the same direction as Dave's.

These come up quite regularly on Ebay, so I'm not really sure it is worth repairing. Other than the battery issue though, it looks pretty well engineered.


Offline jaycee

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #2 on: August 15, 2013, 12:14:52 am »
Unfortunately this is very common on computers of this era with battery backed clocks and suchlike. There are plenty of Commodore Amigas which also suffer the same fate, particularly the A500+ and larger A1000/2000/3000/4000 models which had a battery backed RTC.

If caught early enough they can usually be restored. The usual recommendation is to use something alkaline to neutralise the battery acid from doing further damage.
 

Offline MrAureliusR

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #3 on: August 15, 2013, 12:36:05 am »
As I said on YouTube comments, I think this could be a GREAT restore video, or short series of videos. Just get in there and really scrub with Electrolube IPA, then something to stop corrosion... jump broken traces with thin wire and a steady hand, replace all the off-the-shelf components  (which it looks like they basically all are) and bob's your uncle! I think this could seriously be a very popular video that beginners and experienced EE's alike would find incredibly interesting to watch -- in incorporates many of the things you've done tutorials on together in one job, to show how you attack something like this methodically etc etc. I personally find it very satisfying to restore something this far gone than just a simple 'replace a few caps' job...

Anyway, if you're totally uninterested in doing it, there's a good chance fellow YouTuber jpkiwigeek would be interested in repairing it - he basically fixes old broken computers and documents his really incredible collection of vintage stuff. Plus he's a fellow "from down under"-er...  :-+ :-+

I suppose, like most of us, you've probably got more going on that's of more interest to the blog though, so maybe this isn't an ideal project...

[EDIT] Someone suggested sanding down the problem areas, to get through the solder mask and to the traces. Then use conductive paint/epoxy or something similar to repair! That's an even better idea than what I was thinking. I mean, this could seriously be a cool way to show how to come up with a novel approach to fix something like this. The sand/conductive paint is just one option. I'm sure there are many other ways!
« Last Edit: August 15, 2013, 12:46:48 am by MrAureliusR »
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Offline c4757p

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #4 on: August 15, 2013, 12:43:28 am »
I agree. You've got the makings of a very good short series here, Dave.
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Offline Zad

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #5 on: August 15, 2013, 01:49:47 am »
Way back when this Archimedes beastie was being made, I got myself £1000 worth of Technics hifi for £90 by doing this sort of repair. The tuner had been dropped in the shop and split the PCB in 2 - there was only a small dink in the case to show for it too. Unfortunately for the shop, all the remote control signals for the separates went through the tuner, so it was essentially useless (or so I convinced them). The PCB was only double sided, but the track widths were surprisingly fine and dense. An ideal job for a slightly short-sighted teenager.

A few metres of 30AWG Kynar, a fibreglass pencil and a couple of hours had it sorted. Those fibreglass pencils are excellent for this sort of repair work.

Offline gslug

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #6 on: August 15, 2013, 02:52:29 am »
I still have an Archimedes 310, though I haven't used it in years. That has a couple of AA batteries mounted off-board and connected to a header on the PCB. I didn't realise that the A3000 used a coin cell.

The leakage problem seems to be common in a lot of 1980s electronics. I have a few synthesisers which use battery backed RAM to store the patches. So far I have been lucky, but whenever I get a "new" toy, the battery is one of the first things I check.

BTW, this is my first post here so I guess I should say Hello!
 

Offline Tothwolf

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #7 on: August 15, 2013, 03:56:36 am »
That board really doesn't look too bad compared to some. The trick is to neutralize the alkaline solution that's corroding the metal parts and traces. I've used this cleanup technique probably 100s of times and it should give you pretty good results: http://www.classiccmp.org/pipermail/cctech/2012-October/098565.html
http://www.classiccmp.org/pipermail/cctech/2012-October/thread.html#98562

I don't really recommend sanding off the solder mask unless you need to repair a trace. Once you neutralize the alkaline mess, the small amount of tarnish/corrosion under the solder mask won't really cause any further trouble.

On the upside, the ROM socket damage also gives you a good excuse to replace the cheap leaf contact sockets with higher reliability machined pin sockets. You may find that you need to pre-tin the solder pads with fresh solder and a liquid flux before installing the new sockets. (I generally just desolder, re-tin, and then desolder again before fitting the new components.) Some battery electrolyte solutions can do some really weird stuff to these solder connections and make resoldering them quite tricky if you don't remove the old contaminated solder.
 

Offline orin

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #8 on: August 15, 2013, 04:23:19 am »

If caught early enough they can usually be restored. The usual recommendation is to use something alkaline to neutralise the battery acid from doing further damage.


It's a NiCd - the electrolyte is alkaline.   If you wanted to neutralize it, you'd have to use an acid.

There are some that say that neutralizing with an acid runs the risk of insoluble precipitates that you'll never get ride of, so it's best just using plain water.

I'd give it a good old rub-a-dub with plain water, followed with distilled or de-ionized water, followed with iso-propyl alcohol to help get rid of all the water.  Bake at 150 deg F for a few hours to dry it out.  Pick your own temperature - 150 shouldn't do anything any harm.

I have a Fluke 731B in need of this treatment.  Fortunately, someone caught it before it got anywhere near as bad as Dave's Acorn.  I keep putting it off since the unit is working.  Whoever cleaned it in the past didn't get all the contamination off the board.  You can put a test lead on a trace and run another alongside on the board and read about 3M ohms.

The problem is on the power supply board which is a low impedance point, so it shouldn't be much of a problem (and it isn't as far as the output voltage is concerned), but the leakage is to the guard terminal - it makes the guard terminal useless.

In my case, I'll have to unsolder the bridge rectifier as the contamination clearly goes under it.  Between the contamination and desoldering, the plated through holes will likely be destroyed.  I have a pcb repair kit with eyelets/funnelets* waiting in the wings... I already have repairs to do where the battery connector header pin was broken off.  No solder mask, so the battery wire is soldered directly to the trace at the moment.

Orin.

*that does seem to be the usual spelling, though I've seen 'funnelette' too.
 

Offline orin

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #9 on: August 15, 2013, 04:49:26 am »
Shame about the Acorn being in such poor shape.

In the early to mid eighties, in a former life, I went to Acorn in Cambridge to look at putting Unix on the original ARM chip.  Nothing ever came of it* to my knowledge - the ARM chip at the time wasn't that suited to Unix - they had separated their supervisor/user modes too well.  What they had done was produce an amazing CPU chip for its time given their resources.  Personally, I'd probably have preferred the NatSemi 16032 for ease of programming, but where did that go?

Decades passed and I didn't use the ARM architecture to my knowledge before the Luminary Micro Stellaris chips in the last decade.  The RISC premise worked and still works.

I went onto the Intel 286 (UGH!) and 386 (slightly less UGH!).  The baggage the Intel chips carry to still support the segmented architecture is amazing.  (Though occasionally it was useful when the behind the scenes segment limits weren't reset when the chip went back to real mode.  You could set the limits to 4GB in protected mode, return to real mode and access all memory using 32bit instructions!  Remember himem.sys?  It used that trick.)

Orin.

*at that time of course ;)
 

Offline Tothwolf

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #10 on: August 15, 2013, 05:41:13 am »
If caught early enough they can usually be restored. The usual recommendation is to use something alkaline to neutralise the battery acid from doing further damage.

You mean a mild acid (such as white vinegar).

Alkaline, NiCd, NiMH, etc have an alkaline electrolyte, not acid. You'd use a mild acid like white vinegar to neutralize it, followed by a water rise and something like baking soda to to neutralize any residual vinegar, followed by another clear water rinse. Alkaline, NiCd, NiMH, etc tend to be pretty easy to clean up after, but carbon zinc "heavy duty" batteries often make a huge mess and stain everything (even plastics) bright orange.
 

Offline true

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #11 on: August 15, 2013, 06:45:17 am »
Ctrl in this position is a relic of the IBM XT, and really it makes more sense as it is on the Acorn than the position we have it in now...
 

Offline mikeselectricstuff

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #12 on: August 15, 2013, 06:50:45 am »
Acorn had some "history" with batteries - on the BBC Master, the last of the 6502 range, they used an AA lithium cell, and had a couple of "being on fire" incidents in schools, I think due to reverse-charging through diode leakage.
They did an ugly field replacement using a pack of 3 alkaline AAs on a metal plate which screwed into a rarely used peripheral slot, and subsequently became very cautious about batteries, tending to use alkalines or nicads in future models.
 
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Offline G7PSK

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #13 on: August 15, 2013, 08:22:44 am »
I have found that the best thing for removing corrosion from battery electrolytes whether acid or alkaline in nature is soap and water, seem to neutralise both as well as dissolving the residue and when you have that much spillage it really doesn't matter immersing the whole board in water just rinse with fresh water and then alcohol and place in a warm oven to dry, about 50 or 60 deg C. for a while or sit on top of the hot water cylinder overnight. 
 

Offline Psi

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #14 on: August 15, 2013, 08:56:27 am »
Here's how i'd approach the repair.

- Unsolder every component within the area and keep note of values and locations.
- Remove all the soldermask from the area with some sandpaper. This will remove any loose/corroded tracks as well, all that will remain is the intact copper which makes it obvious where the breaks are.
- Tin all exposed copper with solder
- Solder bare wire along and over the top of any broken tracks
- Spray with pcb lacquer
- Reinstall components
- Test
« Last Edit: August 15, 2013, 09:00:28 am by Psi »
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Offline MrAureliusR

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #15 on: August 15, 2013, 01:12:42 pm »
Hey Dave -- on second thought if you don't feel like repairing it feel free to send it to me and I'll make a video series out of it :D  :-+

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« Last Edit: August 15, 2013, 02:31:10 pm by MrAureliusR »
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Offline rolycat

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #16 on: August 15, 2013, 02:27:55 pm »
In the early to mid eighties, in a former life, I went to Acorn in Cambridge to look at putting Unix on the original ARM chip.  Nothing ever came of it* to my knowledge - the ARM chip at the time wasn't that suited to Unix - they had separated their supervisor/user modes too well.


Acorn did produce an ARM2-based Unix machine in the eighties - the R140, which cost £3,500 when it was released in September 1988. The machine was adapted from the A440. The OS was called RISC iX and was based on BSD4.3 Unix.

As far as I know it was the first commercially available ARM Unix computer.




 

Offline LaurenceW

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #17 on: August 15, 2013, 04:17:27 pm »
It's a question of return on investment, isn't it? No doubt if somebody's LIFE depended on it (and like, this was the last A3000 on the PLANET), then Dave could repair it, yes. But given the state it's in, this is a big ask, just for the "fun" of it. Especially when "other Acorns are available."

I'd share Dave's reluctance to invest time on this one. Part of being an EE is knowing when to bail out.
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Offline orin

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #18 on: August 15, 2013, 05:08:15 pm »
In the early to mid eighties, in a former life, I went to Acorn in Cambridge to look at putting Unix on the original ARM chip.  Nothing ever came of it* to my knowledge - the ARM chip at the time wasn't that suited to Unix - they had separated their supervisor/user modes too well.


Acorn did produce an ARM2-based Unix machine in the eighties - the R140, which cost £3,500 when it was released in September 1988. The machine was adapted from the A440. The OS was called RISC iX and was based on BSD4.3 Unix.

As far as I know it was the first commercially available ARM Unix computer.

That was a few years later then.  I wonder who did it.  Did they do it themselves or was it Logica/SCO?

 

Online AndyC_772

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #19 on: August 15, 2013, 06:59:53 pm »
Looks like they did quite a few Unix boxes, not that anyone really ever bought them.

http://acorn.chriswhy.co.uk/RISCiXComputers.html#R140

The original Archimedes ran an OS called "Arthur", later updated to RISC OS version 2. The RISC OS 3 ROMs that Dave identified as probably being newer than the rest of the unit were indeed an upgrade.

I still have a set of the original RISC OS 2 ROMs, manufactured by Toshiba, sitting in a drawer from when I upgraded my own A3000 back in the early '90s!

It was a nice machine - remarkably fast and capable for its day - but always suffered from a lack of memory, and its early performance advantage over the competition was never really maintained. The ARM2 processor could, on many machines, be removed and upgraded to an ARM3 processor on a carrier board, which added a cache and a speed boost to 25 or 33 MHz. RAM upgrades were costly, and the genuine Acorn 2MB upgrade (1MB on the main board + 1MB on the expansion board) on Dave's machine was quite uncommon as there were plenty of cheaper, functionally identical 3rd party alternatives.

After a few years I upgraded from the A3000 to the newer A5000, which had the ARM3 processor, a built in IDE controller and room inside the case for a hard disc - an expensive peripheral which was only just becoming commonplace. It also had a faster video clock, which allowed it to display higher resolutions and was really worthwhile.

The GUI was attractive and usable, and there's never been an easier machine to start programming since. At any time, press F12 and the GUI scrolls up and you have a command line. Type 'BASIC' and you get BBC BASIC version V, which includes a full ARM assembler. C was available as a commercial package from Acorn and I regret not learning it back then - but there was no need, BBC BASIC was so fast and capable.

Despite the fact that RISC OS used co-operative rather than pre-emptive multi-tasking, it was a lovely machine to use, and way ahead of the competition in many ways. Unfortunately it never caught on commercially in the way the PC did. I still miss my A5000.

Offline nathanpc

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #20 on: August 15, 2013, 07:06:19 pm »
Dave really has the worst luck ever in terms of getting products to make a repair video, they are either working or seriously damaged like this one, but I think this would make for a great "extreme" repair video, but it would take a lot of time and patience to repair it like he described in the video.
« Last Edit: August 15, 2013, 07:08:46 pm by nathanpc »
 

Offline c4757p

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #21 on: August 15, 2013, 07:09:30 pm »
I'd share Dave's reluctance to invest time on this one. Part of being an EE is knowing when to bail out.

True. Still, if he were willing to put in the work (I know he's very busy, though), I think this could be a great opportunity for a very popular and informative video series. There are a lot of people interested in this kind of repair work.
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Offline jahonen

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #22 on: August 15, 2013, 08:21:19 pm »
This video reminded me that I really should remove the NiCd battery from Amiga 4000 that I still have lying around. Fortunately I already had replaced the battery once. There was no leakage from the battery, but I still removed it as one can never know if the battery decides to leak. I intended to remove the charging resistor and run the RTC backup from lithium battery but didn't bother with that. Ended just removing the NiCd battery.

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Offline Spunky

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #23 on: August 15, 2013, 08:28:03 pm »
I used to fix these back in the 90s, and I too would bail out upon seeing that mess. The problem for me was knowing I'd never get paid for my time if it took more than 2 hours.

Great to see one of these old micros again though. I smiled when I saw Dave unscrewing the disk drive...and sure enough it fell out. LOL
 

Offline Stonent

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Re: EEVblog #507 - The First ARM Computer - Acorn Archimedes A3000
« Reply #24 on: August 15, 2013, 09:01:26 pm »
I haven't watched the video yet because I'm at work, but was there ever an NTSC version of this released?
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