A3000 Battery Damage Repairs

discuss the archimedes & risc pc, peripherals and risc os/risc os on pi
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hatchcliff
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Re: A3000 Battery Damage Repairs

Post by hatchcliff » Thu Apr 18, 2013 9:37 am

Naomasa298 wrote:Hopefully, replacing the socket will cure it.
I'm really interested in your technique for removing these large sockets. Would it be possible to provide some description or photographs?

In the very first picture in this thread, some blue discoloration is just visible on the leftmost (disused) connections on the ROM 4 socket. It looked pretty bad before the cleanup, and it occurred to me that there might be damage in this area. Fortunately it turned out there was none, and when I fitted full sized RISC OS 3.11 ROMs later even the discoloured connectors were fine.

I did wonder how I would have removed these sockets if necessary though.

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Re: A3000 Battery Damage Repairs

Post by Naomasa298 » Thu Apr 18, 2013 10:41 am

cliffh wrote:
Naomasa298 wrote:Hopefully, replacing the socket will cure it.
I'm really interested in your technique for removing these large sockets. Would it be possible to provide some description or photographs?

In the very first picture in this thread, some blue discoloration is just visible on the leftmost (disused) connections on the ROM 4 socket. It looked pretty bad before the cleanup, and it occurred to me that there might be damage in this area. Fortunately it turned out there was none, and when I fitted full sized RISC OS 3.11 ROMs later even the discoloured connectors were fine.

I did wonder how I would have removed these sockets if necessary though.
I'll let you know once I've done it successfully. :lol:

I've had another machine with some bad discolouration on the sockets, but they were ok. In this case though, the metal connector in the pin socket has actually corroded through and broken in half, so it'll need to be replaced. Fortunately, the legs of the ROM itself are ok.

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Re: A3000 Battery Damage Repairs

Post by paulv » Thu Apr 18, 2013 2:21 pm

With turned pin sockets, I break them whilst in place by cutting the plastic out that links the two rows of pins, then I snip the plastic between each pin.

It means you write off a socket but by allowing each pin to be removed individually, you're much less likely to damage the PCB.

Paul

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Re: A3000 Battery Damage Repairs

Post by hatchcliff » Thu Apr 18, 2013 5:00 pm

Thanks Paul, that's very useful information. :D

Best Regards

Cliff

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Re: A3000 Battery Damage Repairs

Post by Naomasa298 » Fri Apr 19, 2013 12:25 am

Machine 2's mouse proved easy to fix. None of the tracks on the underside of the board were damaged, so a quick touch of the soldering iron to the pins to melt and reform the solder fixed it. If only they were all that easy to resolve...

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Re: A3000 Battery Damage Repairs

Post by paulv » Fri Apr 19, 2013 1:07 am

Yay! It looks like my initial diagnosis/advice was spot on for all three machines :D

Nice to hear that they're all working or well on their way to working again. When you remove the ROM socket in the other machine take the time to check the tracks under there too. It'll be easier to do with the socket removed :D

Paul

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Re: A3000 Battery Damage Repairs

Post by hatchcliff » Fri Apr 19, 2013 9:04 am

2 out of 3 machines rescued - well done! Hope you can make it 3 out of 3. [-o<

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Re: A3000 Battery Damage Repairs

Post by Naomasa298 » Tue Apr 23, 2013 8:43 pm

cliffh wrote:2 out of 3 machines rescued - well done! Hope you can make it 3 out of 3. [-o<
Removing the socket proved easy enough. I followed paulv's advice and cut the socket's plastic in order to remove the legs one by one. There was so much corrosion that some of the legs just broke away on their own at the point of contact with the motherboard. For those, I just withdrew the pins from the underside of the motherboard. Checked all the tracks and everything seems ok.

I have another problem though - link L13 was also badly corroded and snapped off while I was doing it. I shall have to display my ignorance here - as it's a zero-ohm resistor, can I just solder a piece of wire across in its place?

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Re: A3000 Battery Damage Repairs

Post by jms2 » Tue Apr 23, 2013 8:52 pm

That's what I did - so I hope its ok!

My mouse socket is all corroded inside so the mouse still doesn't work though. :(

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Re: A3000 Battery Damage Repairs

Post by hatchcliff » Thu Apr 25, 2013 9:16 am

Naomasa298 wrote:as it's a zero-ohm resistor, can I just solder a piece of wire across in its place?
This puzzled me too. It seems clear that a piece of wire will do, but why on earth would the design specify a zero ohm resistor :?:

I found the answer in Wikipedia:

"A zero-ohm link or zero-ohm resistor is a wire link used to connect traces on a printed circuit board that is packaged in the same format as a resistor. This format allows it to be placed on the circuit board using the same automated equipment used to place other resistors instead of requiring a separate machine to install a jumper or other wire. Zero-ohm resistors may be packaged like cylindrical resistors, or like surface-mount resistors."

Glad to hear the socket came out OK. :)

Best Regards

Cliff

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Re: A3000 Battery Damage Repairs

Post by 1024MAK » Thu Apr 25, 2013 10:03 am

Ah, zero ohm resistors. If they ever get room temperature superconductors then we can have real zero ohm resistors :lol:

Back in the real world, I have seen boards with machine fitted naked wire links. They are however only common on keyboard PCB's.

Note, one thing to watch out for, is some components that look a little like zero ohm resistors are in fact fuses...

Mark

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Re: A3000 Battery Damage Repairs

Post by Naomasa298 » Thu Apr 25, 2013 11:54 pm

Well, we have progress, sort of. Soldered in a new ROM socket, and also replaced L13 and L14 (which had also surreptitiously broken). No longer getting a ROM checksum error, which is good, and the machine now always gets to the red screen in the POST sequence - before, it would sometimes get there, but would get stuck on the flashing cyan/magenta screen.

Now the drive code indicates a MEMC protection failure and MEMC CAM mapping failure. Does anyone have any experience with these errors, and/or have a diagram of the area around the MEMC chip?

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Re: A3000 Battery Damage Repairs

Post by jms2 » Sat May 04, 2013 11:35 pm

Some progress on my A3000 keyboard here. Paulv's suggestion that there was probably a broken track between the keyboard sockets and IC4/IC5 turned out to be correct!

I was curious as to why the pattern of broken keys didn't match up to the keyboard row/column list in the A300 component level service manual supplement (which is the only publication covering Arc keyboards that I've been able to find). The explanation is simple - the details given aren't correct for the A3000. They may even not be correct for the A3xx and A4xx models as well, I don't know.

Anyway, to help future A3000 keyboard menders, here are my diagrams of how the keys are connected.

I can't explain the multiple pads under the return key. This isn't an error, it is what's really there on the membrane - but maybe there isn't a keyswitch next to every pad, perhaps a couple of them are optional.
A3000 keyboard cols.png
A3000 keyboard cols.png (634.63 KiB) Viewed 2204 times
A3000 keyboard rows.png
A3000 keyboard rows.png (568.74 KiB) Viewed 2204 times

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Re: A3000 Battery Damage Repairs

Post by hatchcliff » Sun May 05, 2013 10:22 am

Congratulations \:D/ . Am I right in thinking that one of your two machines is now in full working order?

Thank you for solving the keyboard mapping puzzle. I was using the A3000 Technical Reference Manual, and it never occurred to me that the keyswitch mapping table could contain so many errors (I assumed I must be misreading it somehow). I suppose the mapping for a different machine must have accidentally found its way into the wrong manual. :shock:

Great diagrams too :D . I'm sure these will help to take some guesswork out of future restoration projects. They confirm that in my case I had three failed rows towards the right of the keyboard.

Best Regards

Cliff

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Re: A3000 Battery Damage Repairs

Post by paulv » Sun May 05, 2013 11:23 am

Congrats on the repair and some very cool work on the keyboard mapping. As Cliff says, it'll come in useful for future repairs.

Paul

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Re: A3000 Battery Damage Repairs

Post by jms2 » Sun May 05, 2013 12:08 pm

cliffh wrote:Congratulations \:D/ . Am I right in thinking that one of your two machines is now in full working order?
Not quite - I haven't actually done the repair yet! Its easy to do though, so I don't anticipate problems.

The other issue on this machine is the mouse port. This is all gummed up with green stuff and the mouse doesn't work. However last night I started the job of sticking a pin into each of the holes and checking for continuity. Only had time to check out the top row but these seemed OK. It is possible that instead of open circuits I may be seeing shorts due to the gunk. Also it could be a couple of broken tracks as with the keyboard.

What I need to decide is whether to order a new Schurter mini-DIN socket from Farnell as detailed in another thread.

As for the second A3000, I haven't been back to that one - but I am starting to wonder whether the keyboard microcontroller (IC1 I think) might have failed. If so, I can swap with the good machine and see if that fixes it.
I suppose the mapping for a different machine must have accidentally found its way into the wrong manual.
I forgot that the same information is also in the A3000 manual. I was looking in the A300 manual because I thought there might be a better explanation in there (there is actually, its a bit longer). I suspect that actually all Arc keyboards are wired like this - it seems to have been done to avoid key clashes. The published information has possibly always been wrong.

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Re: A3000 Battery Damage Repairs

Post by jms2 » Thu May 09, 2013 10:11 pm

I've successfully fixed the keyboard! :D

I have also repaired the mouse circuits, but the mouse itself still doesn't work. I think this must be due to the buildup of corrosion inside the socket, so I'll need to get a new one I think.

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Re: A3000 Battery Damage Repairs

Post by jms2 » Sat May 11, 2013 2:16 pm

With the problems on machine 2 reduced to just a dodgy mouse socket, I've started to attack machine 1 (the dead one) using the oscilloscope. This is what I've managed to find out so far:

Good things:
- 5V present on the board
- RST goes high when you press the reset button
- There is a 24Mhz clock on LK28 and on IC41 (VIDC) pin 19.
- I get a 2.6Mhz RAS signal at R133 and pin 9 of all the DRAMs.

Bad things:
- No CAS signals at R129-R132.
- Clock signals at pins 1 & 2 of IC37 (ARM) seem to fluctuate, not consistently 8Mhz.

Does this suggest anything to anyone? Failed MEMC perhaps? :(

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Re: A3000 Battery Damage Repairs

Post by SarahWalker » Sat May 11, 2013 3:07 pm

A fluctuating ARM clock signal is normal, MEMC varies the frequency depending on the current access. Lack of CAS signals suggests that either MEMC is broken, or RISC OS is stuck in the very early stages of startup, and hasn't got as far as programming it yet.

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Re: A3000 Battery Damage Repairs

Post by jms2 » Sat May 11, 2013 3:25 pm

OK, thanks Tom, I'll do some more testing.

Its encouraging to think that MEMC isn't necessarily trashed. This machine worked perfectly up until the point when it suddenly failed for no apparent reason other than a slightly crusty battery.

I'll check all the address and data lines around the ROM sockets - although they look fine, they are vulnerable to battery acid and would certainly prevent Risc OS from booting.

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Re: A3000 Battery Damage Repairs

Post by Naomasa298 » Sat May 11, 2013 8:33 pm

jms2 wrote:OK, thanks Tom, I'll do some more testing.

Its encouraging to think that MEMC isn't necessarily trashed. This machine worked perfectly up until the point when it suddenly failed for no apparent reason other than a slightly crusty battery.

I'll check all the address and data lines around the ROM sockets - although they look fine, they are vulnerable to battery acid and would certainly prevent Risc OS from booting.
I'll watch your progress with interest, as my dead A3000 also has a problem with the MEMC. Keep us updated!

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Re: A3000 Battery Damage Repairs

Post by retroclinic » Sat May 11, 2013 8:39 pm

As:

a) A get out of trouble solution, if your board is toast, and
b) A shameless marketing plug...

I've got a couple of spare working A3000 motherboards :D Trouble is....finding them may prove difficult in all this "junk" "stock" I still have!

Mark.
Image

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Re: A3000 Battery Damage Repairs

Post by jms2 » Sat May 11, 2013 10:01 pm

I reckon I've cracked it... three of the four roms are not connected to nOE. This is pin 2, right next to the battery.

Thanks for the motherboard offer though Mark - I may still need it!

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Re: A3000 Battery Damage Repairs

Post by 1024MAK » Sat May 11, 2013 10:34 pm

jms2 wrote:I reckon I've cracked it... three of the four roms are not connected to nOE. This is pin 2, right next to the battery.
That's not good :(

Looks like you are going track tracing then... Best go study the circuit diagram / schematic...

Mark

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Re: A3000 Battery Damage Repairs

Post by jms2 » Sat May 11, 2013 10:50 pm

Fixed the pcb track problem - now three of the four roms are connected!

The reason why I am not getting all four is apparently because of a poor pin/socket connection. I'll lever rom 3 out and try to fix it.

EDIT:

It boots! :D

The only remaining issue is that all the keyboard LEDs are intermittent. Flexing SK7 by applying light pressure to its exterior seems to fix it, as does flexing the cable. I'll try some switch cleaner tomorrow.

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Re: A3000 Battery Damage Repairs

Post by jms2 » Sun May 12, 2013 9:37 pm

Switch cleaner has worked and the machine is now happily running again! :D

The list of faults is pretty trivial now -

1) Caps Lock LED doesn't seem to work (this was always faulty before, I think its the LED itself rather than the connections to it).
2) One rubber foot unstuck at the back, and both of them look too small to be the original items.

I can live with those! :D

So in summary, if your battery leaks, these are the things that could go wrong:

a) CMOS RAM chip. These are a PCF8583, and are available on Ebay. If you renew one, it might be a good idea to socket the replacement.
b) Keyboard - either due to broken PCB tracks, failure of IC4, IC5 or IC10, or gunk affecting SK7. All the ICs are available and replaceable, but I have not found a direct replacement for SK7. Note that some forms of damage will prevent the POST error code from flashing the floppy disc light (because this signal goes through SK7).
c) Mouse - damage to PCB tracks, zero-ohm resistors or socket. Resistors can be replaced with wire links and apparently-compatible replacement sockets are available from Farnell, though nobody has tried them out yet!
d) ROMS - check especially the pins nearest the battery. Pin 1 on each rom should be connected to pin 1 on the other three, etc. If the rom connections are damaged the machine will not boot at all and you won't see a POST error sequence.

Pretty much all of the above is fixable with access to the circuit diagram, a multimeter, a sharp soldering iron, side cutters and Kynar wire. So don't despair!

As a result of fixing "machine 1" I no longer have a lot of enthusiasm for fixing "machine 2" that I bought in a moment of weakness as a donor (and which I described repairing earlier). This machine is cosmetically quite reasonable, boots to the desktop, and contains Risc OS 2. The battery damage was quite extensive but I believe I have repaired it all except for needing a new mouse port. So if anyone is interested in an A3000 project, PM me.

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Re: A3000 Battery Damage Repairs

Post by hatchcliff » Tue May 14, 2013 10:52 am

Good to hear your machine is running again =D> =D> =D> .

Great summary! There are several surface mounted resistors and capacitors close to the battery which were drenched in battery fluid in my case. The crystal is fairly close too. I haven't heard of any cases of these failing, but I wonder if they should be added to the list.
jms2 wrote:I no longer have a lot of enthusiasm for fixing "machine 2" that I bought in a moment of weakness as a donor
I wouldn't call the acquisition of a donor machine a moment of weakness, but then I have the hoarder gene turned full on in my DNA. I inherited this from my father who would routinely buy bargain electronic gadgets in threes: one to use, one for a spare, and a spare for the spare. So true to form, I have three working A3000's.

I hope you find a good home for your second machine, prospects for repair of the mouse port seem pretty good.

Best Regards

Cliff

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Re: A3000 Battery Damage Repairs

Post by jms2 » Tue May 14, 2013 12:07 pm

I should add that I've now had an expression of interest for "machine 2" so consider it provisionally sold.

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Re: A3000 Battery Damage Repairs

Post by paulv » Tue May 14, 2013 12:09 pm

1) Caps Lock LED doesn't seem to work (this was always faulty before, I think its the LED itself rather than the connections to it).
I've got some spare LED's if you want a couple for postage.

Paul

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Re: A3000 Battery Damage Repairs

Post by jms2 » Tue May 14, 2013 12:14 pm

I might just take you up on that offer Paul, as it is slightly annoying to not know whether caps lock is on or not!

That said, its a bit unusual for an LED to actually fail so maybe there is a bit of fluff or corrosion under the contacts or something like that. I'll have a little look first.

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