A540 Help needed

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Trisomie21
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A540 Help needed

Post by Trisomie21 » Wed Jan 01, 2020 8:56 pm

On my A540 i had to remove the socket of IC58 due to damage from an leaking battery.

In this process, so it seems, some tracks of the Main pcb got damaged.

Can somebody help me with the correct routing of this Tracks to get it back into working Order?

Thanks a lot!
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IanS
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Re: A540 Help needed

Post by IanS » Wed Jan 01, 2020 9:04 pm

IC 58 is the IOC.

All details are in the TRM diagrams.

http://chrisacorns.computinghistory.org ... s.html#TRM
http://chrisacorns.computinghistory.org ... awings.zip (IOC is on page 3)

Is the chip still ok?

Trisomie21
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Re: A540 Help needed

Post by Trisomie21 » Thu Jan 02, 2020 8:19 pm

I got the A540 in a non working condition, so I dont know of the IOC is still working.

Is there a way to test it or just in this machine or in an other Archimedes?

Thank you for the links for the technical documents.

How to find the brocken tracks? Just doing an continuity test?

Thank you!

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IanS
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Re: A540 Help needed

Post by IanS » Thu Jan 02, 2020 8:46 pm

Trisomie21 wrote:
Thu Jan 02, 2020 8:19 pm
I got the A540 in a non working condition, so I dont know of the IOC is still working.

Is there a way to test it or just in this machine or in an other Archimedes?

Thank you for the links for the technical documents.

How to find the brocken tracks? Just doing an continuity test?
The IOC should work in any other Archimedes where the IOC is socketed, A3xx, A4xx (not A3000).

Continuity from each pin on the socket, to where it should go, following the circuit diagram, should get you there.

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gidandridge
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Re: A540 Help needed

Post by gidandridge » Thu Jan 02, 2020 8:48 pm

Yes if you have a multi-meter then just follow the tracks visual from start to end. Then test it at various points along the way with the continuity function on your meter.

This is, of course, easier said than done. Keep in mind that the if the track seems to stop at a 'hole' then it likely goes though to the reverse side of the board and continues from there. Also the tracks may disappear underneath other components and IC's which makes it tricky! :(

A mixture of the above and also using the schematics that Ian linked you too should get you there. Those will show you exactly where all the lines run to and from.

Once you have confirmed the breaks you can solder in some new wire's.

Good luck :D
Gav. :D

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Acorn Electron Plus 1, AP6, GoSDC, Slogger Pegasus 400

Trisomie21
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Re: A540 Help needed

Post by Trisomie21 » Sun Jan 12, 2020 8:13 pm

I did a lot of testing now and I found two broken connections.

On Pin 17 IOC to IC 75 Pin 3

On Pin 42 IOC to IC 64 Pin 22

Next step will be replacing the socket and fixing wires on the broken tracks.
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Re: A540 Help needed

Post by Trisomie21 » Sun Jan 12, 2020 8:21 pm

This is the socket before it got removed.
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IanS
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Re: A540 Help needed

Post by IanS » Sun Jan 12, 2020 8:23 pm

Trisomie21 wrote:
Sun Jan 12, 2020 8:21 pm
This is the socket before it got removed.
Did the chip clean up ok? Do you have anything else you can test it in?

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Re: A540 Help needed

Post by steve3000 » Sun Jan 12, 2020 10:45 pm

Definitely some damage to the PCB in the first photos, and looks like more than 2 tracks are broken?

For most of those tracks under the socket, you can clearly see where the track is damaged, so double check they are showing good continuity before fitting the socket. Once the socket goes back in the breaks will be harder to pinpoint. The A540 is very rare, and very fussy, so take your time.

Have you treated everything with vinegar to neutralise battery fluid? If you wanted to be really rigorous you could also consider cleaning up the area under the socket further with very light sanding (800 grit wet & dry, masking other areas off first), followed by cleaning with distilled water and IPA, then sealing with green pcb coating...

But I would suggest leaving the actual track wire repairs until after the socket is fitted - then you can run fine wire links between various IC legs on the underside of the board, which keeps repairs invisible once everything is refitted.

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Re: A540 Help needed

Post by Trisomie21 » Thu Jan 16, 2020 4:22 pm

IanS wrote:
Sun Jan 12, 2020 8:23 pm
Trisomie21 wrote:
Sun Jan 12, 2020 8:21 pm
This is the socket before it got removed.
Did the chip clean up ok? Do you have anything else you can test it in?
Yes, I can test it in an working A310 that I have here!
steve3000 wrote:
Sun Jan 12, 2020 10:45 pm
Definitely some damage to the PCB in the first photos, and looks like more than 2 tracks are broken?
You are right, the two broken connections I mentioned in my post are the two that are to difficult to guess, so I repaired the all the other tracks and I test everything and now I´m left with this two.

So, I will see what and how to do, and I will take my time for this to get everything right and correct.

The board is an ISS. C version, and somebody did some handsoldering allready.

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Re: A540 Help needed

Post by Trisomie21 » Mon Jan 27, 2020 11:39 am

On the weekend, I now had the time to fix the socket back and do the track repairs.

I have used fine wire to make the correct connections and put everything back together.

The A540 is back to live again! :D

The only problem that Im left with is, that the disk drive is not recognized and when I add a RAM Module the computer crashes/hangs up! :(
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Kazzie
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Re: A540 Help needed

Post by Kazzie » Mon Jan 27, 2020 12:17 pm

Well done =D>

Time to move on to other parts of the board now, I suppose... :roll:
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Re: A540 Help needed

Post by Trisomie21 » Sun Feb 02, 2020 12:13 pm

So the Floppy Drive is also back to live now. :D

This A540 is running on RIsc OS 2.01 dated 08.03.1990, seems it is an early version of it :?:
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Re: A540 Help needed

Post by steve3000 » Sun Feb 02, 2020 3:13 pm

Oh well done!

May not be the same issue, but I find that my A540 is very fussy with RAM modules changes. I suspect the contacts are a bit iffy, as it always has problems after changing RAM or CPU card, requiring several attempts to refit/reseat them before it springs into life.

I notice you have the rather uncommon ceramic 35MHz ARM3 on your A540. This is a real find - I've not seen one on an A540 CPU card before - I have seen 26MHz and 30MHz cards, and DIY 35MHz cards...but not the real thing! Check you crystal is 70MHz or more, and you'll easily overclock this to 40MHz or more, with the appropriate crystal.

For RISC OS 2.01, I'm not sure of the release date, but FOX was the code name for the A540 release. Worth checking the available 2.01 download has the same date.

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Re: A540 Help needed

Post by Trisomie21 » Sun Feb 02, 2020 9:06 pm

After the power on self test, which is passed, it takes only some seconds for the A540 to freeze.
Maybe it is the RAM Module. I will get a different one and try it out. Then I will know where to start with.

In the Moment The Quarz is a 52 MHz and it is socketed, so it will be an easy task to change this to a different Type.

I found that the Risc OS 2.01 Version that was used in the A540/R260 Range is dated 05. July 1990. So this one used here is an early one.

The front and the backside of the CPU module.
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steve3000
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Re: A540 Help needed

Post by steve3000 » Sun Feb 02, 2020 9:33 pm

Ok, great, the hand-written serial number certainly suggests this was a prototype (if the early RO2.01 and the hand-soldering on the PCB wasn't enough...)

Is it stable running without a RAM card present, just on the built-in 4mb? And did the RAM card come with the computer, or did you get it separately? - I know RISC OS 2.00 had problems with >4mb fitted (desktop won't load), so if you got the RAM separately, it could be the early RO 2.01 ROMs don't fix all the >4mb issues?

Do you have any way to dump a copy of the ROMs it would be very interesting to see the differences to the release version of 2.01.

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Re: A540 Help needed

Post by waldorfmuppet » Mon Feb 03, 2020 6:31 pm

Out of interest can you say where the A540 came from? It seems odd noone swapped the ROMs for the release version so it may have an interesting history!

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Re: A540 Help needed

Post by Trisomie21 » Wed Feb 05, 2020 11:40 am

No, the ram module Im using here was bought after I got the A540 and on this module there are no markings so I dont even know who produced it.

Yes, it is running stable without the module installed. I played popolous on it and there was no Problem so far.

How can I do a Dump from the ROM´s? Do I Need Spezial Hardware for it or is it working on Software base?

I got this unit from a Garage sale like one and a half year ago. It came with a SCSI Module and a HD (Nothing special on it), so there is not much I know about the history behind it. Sorry!

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Re: A540 Help needed

Post by steve3000 » Thu Feb 06, 2020 10:26 pm

Trisomie21 wrote:
Wed Feb 05, 2020 11:40 am
No, the ram module Im using here was bought after I got the A540 and on this module there are no markings so I dont even know who produced it.

Yes, it is running stable without the module installed. I played popolous on it and there was no Problem so far.
Ah, that could explain it - some A540's were said to be fussy about the RAM cards they accepted, due to the MEMC1a's not being matched, resulting in slightly different timings. It is interesting to note that various 8mb upgrades for the older Archimedes came with matched pairs of MEMC1a's...

My A540 has (eventually) accepted the two different makes of RAM cards I have acquired - although when adding these, the computer did refuse to start several times, or suffer multiple Address Exceptions at boot, which I've put down to slightly iffy sockets - but these issues disappeared with a bit of wiggling of the cards. The issue you have (booting ok, then failing) sounds different.

If the MEMC timing issue is real, then I wonder if these issues were fixed with later software or hardware mods... you clearly have an early A540, with an early version of RO2.01, so your's may be more susceptible to this issue? Could try updating to RO3.1, and scouring the A540 tech. ref. manual for indication of hardware patches?
Trisomie21 wrote:
Wed Feb 05, 2020 11:40 am
How can I do a Dump from the ROM´s? Do I Need Spezial Hardware for it or is it working on Software base?
It's quite easy if the computer is running. Just type the following:

*SAVE ROM201a 3800000+80000

This should produce a 512kb file, which you can transfer out on a formatted DOS disc. :)

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Re: A540 Help needed

Post by IanS » Thu Feb 06, 2020 10:29 pm

steve3000 wrote:
Thu Feb 06, 2020 10:26 pm
This should produce a 512kb file, which you can transfer out on a formatted DOS disc. :)
Didn't DOS disk support (in the OS) come with RISC OS 3?

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Re: A540 Help needed

Post by steve3000 » Thu Feb 06, 2020 10:39 pm

IanS wrote:
Thu Feb 06, 2020 10:29 pm
steve3000 wrote:
Thu Feb 06, 2020 10:26 pm
This should produce a 512kb file, which you can transfer out on a formatted DOS disc. :)
Didn't DOS disk support (in the OS) come with RISC OS 3?
Quite right. So to do this under RO2, you'll need !MultiFS from the PC emulator package or one of many PD DOS disc writers for RO2. If you have a RISC OS 3 Archi to hand, just transfer with ADFS discs, and then onto DOS under RO3.

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Re: A540 Help needed

Post by Trisomie21 » Mon Feb 24, 2020 11:39 am

So, here it is the ROM from the A540. It took me some time, cause my PC was dead, so I had to get this one up and running. No other 3.5" FDD around! :x

I had to add the .txt Extension to it, if not I would not be able to post it here.
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Re: A540 Help needed

Post by Trisomie21 » Mon Feb 24, 2020 11:42 am

And I add now two RAM Modules to it, Acorn original type and they are working properly.

What I notice is that I can not put the module fully inside the socket because this will create Problems, just like 1mm out and it works! A real strange behavior.

Last but not least I got another A540 with battery Damage and I got it also back into working order and all in just a few Hours. :D

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Re: A540 Help needed

Post by TimoHartong » Sun Mar 01, 2020 11:14 am

"Last but not least I got another A540 with battery Damage and I got it also back into working order and all in just a few Hours".
Good news another nice Acorn Machine saved from certain death. Just out of curiosity where did all those A540 come from? I was able to save a R260 also a lot of work and I got an extra memory module from a fellow club member and have now 12 Mbyte of RAM. Looking to see if I can get the last module..;-)

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Re: A540 Help needed

Post by Trisomie21 » Sun Jul 12, 2020 11:15 pm

steve3000 wrote:
Sun Feb 02, 2020 9:33 pm
Ok, great, the hand-written serial number certainly suggests this was a prototype (if the early RO2.01 and the hand-soldering on the PCB wasn't enough...)

Is it stable running without a RAM card present, just on the built-in 4mb? And did the RAM card come with the computer, or did you get it separately? - I know RISC OS 2.00 had problems with >4mb fitted (desktop won't load), so if you got the RAM separately, it could be the early RO 2.01 ROMs don't fix all the >4mb issues?

Do you have any way to dump a copy of the ROMs it would be very interesting to see the differences to the release version of 2.01.
Are you able to find a difference between the two Risc OS2 versions? 🤔

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