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Acorn Archimedes A3000 Repair


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Thanks to old mate @narf_ for sending this over to me.

 

A bit of history on the Acorn Archimedes on the Wiki https://en.wikipedia.org/wiki/Acorn_Archimedes

The significance of this computer is it uses a ARM 2 processor which is the predecessor to processor found in almost all modern technology from phones to TV's

 

I've only assessed the damage to the computer at this stage.

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The is the damaged caused by the leaking battery. I'm going to strip most of the components in the area with the exception of the surface mounted caps and resistors and clean it with white vinegar. The roms to the right are for the Risc OS

 

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I turned the psu on last night to see what I did. I recall Narf saying there was no 5 volts., sure enough turning the switch mode psu on gave me that familiar sequel switch mode power supplies make when something is shorted.

Poking around with my multimeter both of these components had dead shorts along with the 2 caps to the right. I will have to remove them from the circuit to confirm whats bad. I can't find any schematics on this PSU so I'm winging it.

The component on the left is a (labeled SCR) TIC126M is a silicon thyristor, U = 600V, I = 7.5A

On the right (labeled D6) C82-004 15A Schottky barrier diode

The two caps C16 and C17 are 2200uf 10 volts

I'll have to see if I can find any equivalents locally.

More to come.

 

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PSU Repair.

 

I've removed the 4 suspicious components to test.

IMG_20200122_112132.thumb.jpg.09ebaee68f5bd22cd74a9ad7e48a332d.jpg IMG_20200122_112045.thumb.jpg.ab6f747e7a60923f50034534e3173157.jpg

These looks ok.

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This capacitor checked out ok.

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Bam here's the culprit with a dead short. (caps were discharged before the test)

I don't know if this has caused any other damaged to the psu. I'll dig around for some replacement caps and report back.

 

 

 

 

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IMG_20200122_161815.thumb.jpg.7c4c17905d2a3a14c850dc8d248db429.jpg

Replaced the 2200uf caps at c16 and c17 and 1uf caps at c14 and c18 and the power supply is now working.

Initially I was worried about getting 6 volts but this is without a load. Once a load was applied it droped right down to 4.6 volts with the adjustment pot turned all the way down.

Edited by Arcade King
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How do you approach cleaning corrosion damage on the PCB like this? Strip the components away, wash with vinegar and let dry? Is there much value in scrubbing off the solder mask and re- seal it, or if there's continuity on the traces etc best to let leave?
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How do you approach cleaning corrosion damage on the PCB like this? Strip the components away, wash with vinegar and let dry? Is there much value in scrubbing off the solder mask and re- seal it, or if there's continuity on the traces etc best to let leave?

 

The tracks are pretty fine so the less scrubbing the better. The plan at this stage is to strip all the IC's and sockets out around that area brush some vinegar over the area wash it off then dry. Next assess the area and lightly go over it with a fibre glass tip pen. Lightly seal then put the sockets and new IC's in. I've got the 74LS145's I'm just waiting on the PCF8583P real time clock chips.

If all goes to plan and she boots up I'll upgrade the Risc OS roms to 3.11.

 

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Anybody know what these 20 pin sockets are called? The lower one has corrosion damage and has damaged the ribbon connector for the keyboard. I'm confident I can repair the ribbon using conductive paint however these sockets really need to be replaced.

 

 

 

 

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Awesome

 

i did get it to boot using an external 5v power supply. Glad its gone to a good home vs the dump or my shed shelf

 

That's a good sign. Apparently holding delete while booting resets the cmos.

To answer my own question about the keyboard connector its a FFC & FPC Connector made by TE Connectivity part number 7-520355-0 available from Mouser :D

 

 

 

 

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Area cleaned up ok with vinegar, tracks look in tact however all the zero ohm jumpers are falling apart.

The biggest concern is melting the solder on the underside causing through hole and track damage due to the alkaline getting into the solder.

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I'm going to desolder all the parts with my desoldering station. I usually add new solder to the joints to make it easier but the problem is when the corrosion eats into the solder it changes it (somebody with brains can chime in here) and can make it impossible to melt.

This board doesn't look too bad at first glance however the corrosion has reached the underside joints which could make life difficult. Hopefully I'll have some time on the weekend to get stuck into it.

 

Side note.

The roms were 1 meg Fujitsu MB831000 mask roms.Two of them are bad and from the other two I worked out this was running Risc OS 2.0. I'm going to upgrade it to OS 3.11 using 4x4 meg roms.

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Parts stripped, I also removed those furry jumpers on the bottom. Surprisingly all the sockets and IC's came out easy but the zero ohm jumpers not so much. I've already found 3 bad traces just above IC6 so I'm sure there will be more mainly due to the corrosion damaging the plated through holes :( IC10 74hc74 also tested bad. I gave the area a light once over with the fibre glass pen trying to avoid damaging tracks.

It just goes to show no matter how good a battery damaged board cleans up there's always underlying damage.

Looking at pictures from other peoples repairs R7 180ohm surface mounted resistor is missing. What I'll do is bypass it with a diode and install a 3 volt coin battery and holder. I'm still not sure if I'll use those keyboard sockets yet, they did clean up ok. I got replacements from Mouser but they are dual wipe so I'll need to inset the already damaged ribbon connector in one and see if it goes in ok.

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IMG_20200204_131038.thumb.jpg.8a5790f95ee5a102bcced153b43bc251.jpg IMG_20200204_132128.thumb.jpg.96ff31e3c8e1c66a3060bf44b7a2f310.jpg

Some more progress.

I tested those ribbon connector sockets with the keyboard ribbon and they do work well. I've sourced a replacement 9 pin mini din connector (on the left) from Germany. I'm not sure if it's really needed but I've already replaced everything else. I also have a replacement crystal but the one I got is a lot smaller so if this one still works I'll leave it.

 

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I got a couple of spares of those 20 pin sockets, the old ones are at the top.

 

So now the hard part which is checking all the traces and repairing any bad ones, install a CR2430 battery, burn some Risc OS 3.11 roms and hope all of this was worth the effort :)

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Well some great progress this afternoon.

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Got the thing to boot into Risc OS :D at first I thought there was a fault. The screen wouldn't sync, I could make out Supervisor 2048k and a prompt. Wasted a bit of time thinking this was a fault. I decided to hook up the keyboard and hold DEL while powering on to reset the CMOS and that did the trick.

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Luckily the unique 9 pin mini din mouse came with the system. It's quite possibly the ugliest mouse ever made but it works.

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Not much to do in Risc OS 2 except change a few colour settings and this app which shows the memory usage.

Interesting how the 2 meg ram expansion(left pic) doesn't seem to include the 1 meg onboard ram :unsure Right pic is without the 2 meg expansion installed.

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I want to upgrade to Risc os 3 which uses 4x4meg roms. Apparently the roms floating around need to be byte swapped to use in a real machine same as Amiga Kickstart. It's been a long time since I've messed around with that. I need to find a program to do the job.

Anyway I'd call this a win.

 

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I'm kind of amazed that you didn't after this test!

 

Well I didn't have the best of afternoons. The Mrs Ratbird decided to get in and chew up my expensive Hakko desoldering gun that I just dug out to do some work. It's 500 bucks to replace it.

Somebody up there hates me :(

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Well I didn't have the best of afternoons. The Mrs Ratbird decided to get in and chew up my expensive Hakko desoldering gun that I just dug out to do some work. It's 500 bucks to replace it.

Somebody up there hates me :(

 

:cry Holy shit.

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Worked out how to byte swap the roms so Risc OS 3.11 installed.

Too bad the mouse decided to stop working so I couldn't check it out :( It only moves up and down now :unsure More than likely a problem with a bad track somewhere.

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Nothing I hate more than people who hand out cryptic information and don't fully explain how to do something so here's the easiest and quickest way to join and byteswap the roms to use on real hardware. The roms on the net are memory dumps for use with emulators.

You need 4x4 megabit roms 27c4001 or 27c040

Download the Risc OS 3.11 roms from HERE

Download SRecord from HERE

Download the attached zip file containing a batch file I made up to do the job. (for Windows)

Unzip everything in one folder

Run acorn.bat

You'll end up with 4 roms 512k each named with the socket they need to go in.

Burn the roms and set the jumpers as per the above pic under U17

Enjoy.

Acorn Rom Byte Swap.zip

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Hooked up the Hxc floppy emulator to try loading some games. Unfortunatly the 9 pin mini din mouse connector on the computer needs replacing so I have to keep pressure on the connector to make the mouse work correctly.

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@Womble this ones for you brother.

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Suprised to see Nebulus on here. Fantastic game.

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Everybody knows this game.

Overall im impressed with this computer which is easily comparible to the Amiga. Only thing lacking on this model is a Joystick port however im aware of a mod to turn the serial port into one.

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Pretty much the home stretch now.

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The 9 pin mini din sockets finally arrived from Germany so I desoldered the old one and cleaned underneath.

 

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No wonder I was having issues with the mouse.

 

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All done. I made up some labels for the roms and changed the 40 pin socket for the keyboard/mouse controller.

Sprayed some pcb clear lacquer on the bottom and added a pic so you can see the fixed tracks. All up about 4 or 5 needed to be repaired.

Mouse now works perfectly. I 'd like to make the serial to joystick mod before closing the case and possibly the audio mod that apparently gives it clearer sound.

There's also a modern IDE podule I've been eying off on ebay but at 180 bucks I don't think I'd use this computer enough to justify it :unsure anyway the main repair is now done and the computer has been restored to 100% working order :)

 

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