Battery Damage - A3000

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chinnyhill10
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Battery Damage - A3000

Post by chinnyhill10 » Mon Oct 03, 2016 3:46 pm

Hi,

Some of you may possibly know I run a Youtube channel devoted to using original hardware. The number 1 most requested system for quite a while has been the Archie, but alas funds have never allowed (always seems to get beaten on auctions).

At the weekend an A3000, monitor and loads of stuff turned up locally on Ebay. I bid, and won. Hoorah!

Went and collected it and indeed it was trove. The guy was a retired teacher. He had everything including the original invoices, monitor, stacks of disks and 24 pin printer.

I got it home, switched on and it gave me an error about keyboard missing. Now I knew the A3000 suffered from battery issues and this could be a sign. Sure enough I opened her up and the battery was a mess.

After a clean up with white vinegar and IPA, I removed the battery and started taking a closer look. Some components close to the battery fell apart on touch namely the resisters at L9, L13, L14 and a surface mount (possibly a diode) at R7. There's possibly chip damage but it's hard to say. My electronics skills are limited to soldering caps into Master power supplies. Tiny SMD's like the one that fell off aren't my cup of tea at all.

So does anyone know of a repair service who can help me? I'm very keen to get this machine up and running so I can expand the coverage.

Photo attached of this lovely machines board after I cleaned it up. Of course gunk could still be lurking under the chips. :(

Cheers.
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danielj
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Re: Battery Damage - A3000

Post by danielj » Mon Oct 03, 2016 3:49 pm

Where are you, and can you get to Bolton for the November abug meeting? :D

d.

chinnyhill10
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Re: Battery Damage - A3000

Post by chinnyhill10 » Mon Oct 03, 2016 3:53 pm

danielj wrote:Where are you, and can you get to Bolton for the November abug meeting? :D

d.
Hampshire. So Bolton is a little far.

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1024MAK
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Re: Battery Damage - A3000

Post by 1024MAK » Mon Oct 03, 2016 4:37 pm

The items with a 'L' prefix are RF chokes / inductors, not resistors. Really need the schematic and parts list to know their values and properties.

Mark

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Re: Battery Damage - A3000

Post by chinnyhill10 » Mon Oct 03, 2016 4:40 pm

1024MAK wrote:The items with a 'L' prefix are RF chokes / inductors, not resistors. Really need the schematic and parts list to know their values and properties.

Mark
Thanks. This is why I need someone to take off my hands to fix it. I suspect some traces have gone as well and it needs an expert eye and not a bumbling amateur (which is what I am).

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Re: Battery Damage - A3000

Post by chinnyhill10 » Mon Oct 03, 2016 7:29 pm

A few Acorn users I know on Twitter have recommended a chap called Retroclinic so I've emailed him.

The rest of the stuff seems fine and dandy. A nice Acorn monitor with a SCART connector on the back. Wonderfully useful. Feels like a rebadged Philips to me. Pity they skimped and only put a single speaker in it.

And a 24 pin Star printer for which ribbons are still available. Joy!

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Re: Battery Damage - A3000

Post by jms2 » Mon Oct 03, 2016 7:32 pm

Good news... The "L" things are simply links, otherwise known as zero ohm resistors. They physically resemble resistors, but you can replace them with wire links. That should be within your soldering skills hopefully.

As for the SMD item, that will be a resistor. But there are some redundant bits of circuit in that area, so it might not be needed.

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Re: Battery Damage - A3000

Post by jms2 » Mon Oct 03, 2016 7:36 pm

Looking more closely at your photo, the damage does not look too bad. :D R7 is in series with the battery so when you renew the battery it would be possible to install the resistor off board.

Make sure you clean up those sockets for the keyboard membranes.

This machine looks fixable.

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1024MAK
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Re: Battery Damage - A3000

Post by 1024MAK » Mon Oct 03, 2016 7:38 pm


JonC
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Re: Battery Damage - A3000

Post by JonC » Mon Oct 03, 2016 7:41 pm

Last time I emailed Mark (retroclinic) on something Archie related he said he was focussing on Beebs and wasn't inetersted. :?

That's not to say he won't help you, but just be prepared. #-o
Jon
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Re: Battery Damage - A3000

Post by chinnyhill10 » Mon Oct 03, 2016 10:07 pm

jms2 wrote:Good news... The "L" things are simply links, otherwise known as zero ohm resistors. They physically resemble resistors, but you can replace them with wire links. That should be within your soldering skills hopefully.

As for the SMD item, that will be a resistor. But there are some redundant bits of circuit in that area, so it might not be needed.
Good old Acorn. Always over engineering! Like my Master. In any other machine when a PSU cap goes pop, off goes the machine. The Master just sat there merrily carrying on!

Me repairing it myself will be a last resort. There' s still a Spectrum in the garage that I've been tinkering with for a year. Was bust when I got it and have slowly been working my way through it. If it's left to me the channel will still have no Archie coverage this time next year!
Last edited by chinnyhill10 on Mon Oct 03, 2016 10:09 pm, edited 1 time in total.

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Re: Battery Damage - A3000

Post by chinnyhill10 » Mon Oct 03, 2016 10:08 pm

JonC wrote:Last time I emailed Mark (retroclinic) on something Archie related he said he was focussing on Beebs and wasn't inetersted. :?

That's not to say he won't help you, but just be prepared. #-o
I've popped him an email so hopefully he may respond. If not I'll have to find a plan B.

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Re: Battery Damage - A3000

Post by chinnyhill10 » Mon Oct 03, 2016 10:12 pm

jms2 wrote:Looking more closely at your photo, the damage does not look too bad. :D R7 is in series with the battery so when you renew the battery it would be possible to install the resistor off board.

Make sure you clean up those sockets for the keyboard membranes.

This machine looks fixable.
Didn't have anything fine enough today to get into the crud in the smaller areas. It was a case of get as much as I could off to inspect the damage.To be honest I suspect a couple of the nearby chips could do with coming off to be cleaned (and the board underneath) as well.

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Re: Battery Damage - A3000

Post by danielj » Mon Oct 03, 2016 10:17 pm

If you think there's still crud, I would take the board out, remove any ICs that are socketed and get the vinegar sloshed all over it, give it a rub with an old toothbrush, then get it well rinsed and give it a while to dry. That should at least neutralise the crud even if it's stuck under things.

(I see Mark's reading this thread, I should probably change that to say "give it a rub with an ESD certified carbon-based brush device") :D

d.

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Re: Battery Damage - A3000

Post by 1024MAK » Mon Oct 03, 2016 10:39 pm

While it's wet, a normal toothbrush is fine :D

But don't use toothpaste :lol:

Mark

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Re: Battery Damage - A3000

Post by 1024MAK » Mon Oct 03, 2016 10:41 pm

A set of "jewellers" small screwdrivers, well the flat bladed ones are a handy size for digging rubbish out of places as well.

Mark

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Re: Battery Damage - A3000

Post by chinnyhill10 » Mon Oct 03, 2016 11:01 pm

1024MAK wrote:A set of "jewellers" small screwdrivers, well the flat bladed ones are a handy size for digging rubbish out of places as well.

Mark
Had a set with me but wasn't making an impact on the green inside the connector. Was thinking of finding some fine sandpaper wrap around the smaller screwdriver to get some abrasion on the metal 'teeth'.

Earlier in the year I got an Amstrad PC2086 which had horrific battery leakage (4 AA's worth) that had eaten into the metal casing of the PSU. That was a full on sandpaper job. Came up a treat and finished it off with some WD40. A quick upgrade to a NEC V30 from the stock 8086 and the machine was pressed into service for the Youtube channel.

You have to wonder why Acorn put the battery there in that way. It would have, what, a 5 year life? The one saving grace of the Amstrad was they'd run a connector off the motherboard to a separate part of the case which housed the batteries. Very much like the arrangement in the Master. Just keeps it all away from the vital bits.

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Re: Battery Damage - A3000

Post by leenew » Tue Nov 01, 2016 8:39 pm

Assuming it can be arranged with the relevant parties, I reckon your best shot is to mail the sorry beast to Bolton before the meeting and let the bods have a look at it up there...
Lee.

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Re: Battery Damage - A3000

Post by munchausen » Wed Nov 02, 2016 8:08 am

It's odd, but though I would have assumed those L* parts are inductors I'm pretty sure they are just links. Perhaps someone more familiar with old schematics can have a look, because they are marked in an unusual way, but they don't appear to have any function:
A3000 mouse socket.png
R7 is a 180R resistor in series with the battery (so without it you'll have to keep pressing del on power on).

I'm also in Hampshire, if you want to bring it over some time we could buzz it out and replace the damaged parts (send me a PM).

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Re: Battery Damage - A3000

Post by Richard Russell » Wed Nov 02, 2016 3:57 pm

munchausen wrote:It's odd, but though I would have assumed those L* parts are inductors I'm pretty sure they are just links.
The symbol is quite similar to that commonly used for a Polyswitch resettable fuse (similar to a PTC thermistor), and given their function in the circuit (in series with the mouse socket connections) that seems a likely candidate. Replacing them with wire links would work, but the protection they are designed to provide would of course be lost.

Richard.

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Re: Battery Damage - A3000

Post by chinnyhill10 » Wed Nov 02, 2016 10:13 pm

munchausen wrote:It's odd, but though I would have assumed those L* parts are inductors I'm pretty sure they are just links. Perhaps someone more familiar with old schematics can have a look, because they are marked in an unusual way, but they don't appear to have any function:

A3000 mouse socket.png

R7 is a 180R resistor in series with the battery (so without it you'll have to keep pressing del on power on).

I'm also in Hampshire, if you want to bring it over some time we could buzz it out and replace the damaged parts (send me a PM).
Thank you. The original repair arrangements have fallen through. Really want to get this beastie up and running as it has an interesting history. DM will be incoming shortly!

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Re: Battery Damage - A3000

Post by 1024MAK » Thu Nov 03, 2016 3:49 am

You can see the components denoted as Lxxx in the photo here.

One day I may find the time to work out exactly what they are. But given the lines they are in, and knowing about the RF inductors used in other computers, I still think they are RF inductors. They are used on all lines (including 0V) except for the screening/shield connections. They are unlikely to be any type of fuse, as the power required to blow (or activate in the case of polyswitch fuses) would be greater than that available in most of the circuits. And of course, a RF inductor may well have very little DC resistance.

The case for zero-ohm "resistor" links is even worse. Why would you fit so many if you are trying to keep the production cost low?

Mark

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Re: Battery Damage - A3000

Post by munchausen » Thu Nov 03, 2016 10:53 am

It seems clear they are some kind of filter or input protection, but they also clearly aren't strictly necessary.

They do look like some kind of choke, and it makes sense given that the mouse is essentially just some switches and phototransistors at the end of a wire. But it is still a little odd that they use a different symbol than inductors elsewhere in the circuit, and that their value isn't given.

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Re: Battery Damage - A3000

Post by IanS » Thu Nov 03, 2016 10:22 pm

The clue on the circuit diagram is the "NF", "Not fitted", and as there is space on the board for them, they fitted zero ohm resistors.

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Re: Battery Damage - A3000

Post by munchausen » Thu Nov 03, 2016 10:34 pm

Two black lines on a resistor, 0 ohm and 0 multiplier...

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Re: Battery Damage - A3000

Post by veegee850 » Thu Nov 03, 2016 10:37 pm

They are listed on page 53 of the service manual for the A3000

L1-L13 - Resistor Zero Ohm 0W25
L14 - listed as a wire link but is the 0 Ohm on my Issue 3 board.

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Re: Battery Damage - A3000

Post by 1024MAK » Fri Nov 04, 2016 7:52 am

IanS wrote:The clue on the circuit diagram is the "NF", "Not fitted"
Oops, missed that :oops:

So, presumably the intention was (and maybe they did) fit inductors to "export" models. So as to help reduce the RFI output. But as the UK's regulations were different, they did not see the need to do so on UK models. Hence using zero ohm resistors (machine pickable wire links) instead.

So an insulated or uninsulated wire (depending on the risk of short circuits) can replace any broken or damaged zero ohm links.

Mark

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Re: Battery Damage - A3000

Post by jms2 » Fri Nov 04, 2016 7:56 am

I can confirm wires work fine. That's what I had to use on mine.

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Re: Battery Damage - A3000

Post by munchausen » Fri Nov 04, 2016 8:29 am

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Re: Battery Damage - A3000

Post by poink » Fri Nov 04, 2016 9:41 am

1024MAK wrote:So, presumably the intention was (and maybe they did) fit inductors to "export" models. So as to help reduce the RFI output. But as the UK's regulations were different, they did not see the need to do so on UK models. Hence using zero ohm resistors (machine pickable wire links) instead.
In terms of EMC regulations, the usual reason for NF pads is that if the basic design fails testing, you can spend 15 minutes with a soldering station adding a few caps/inductors etc., at the testing house and finish on schedule. The alternative is having to leave to modify the PCB design, have a new PCB made, assembled, and then going back and paying for a further day of testing. A few additional pads you might not use are just a lot quicker and cheaper.

At the time, it seems likely that Acorn would have been looking for a single model conformant with UK national regulations and the upcoming harmonised EU ones (which were originally expected to be in force within a couple of years).

The area around the RTC in the A3000 is just generally odd though - maybe there was the idea of an 'A3000 with separate keyboard model' as a more direct A3xx replacement? Either way, there seems to have been a desire for variations on the keyboard and mouse - hence the links, the mouse socket, the alternative mouse socket, alternative keyboard socket and ability to disable the 8051's clock.

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