A5000 CMOS Replacement

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nOmArch
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A5000 CMOS Replacement

Post by nOmArch » Mon Feb 13, 2012 3:07 pm

After a rather pleasant run down to Oxford yesterday I came home with Matthew's Faulty A5000 which had suffered the old leaky battery syndrome which had taken the CMOS with it.

Matthew kindly gave me the replacement CMOS he had ordered and wished me luck.

Finally had a chance to get the case off and have a look earlier and here are the results.

Image

Image

As you can see the battery did quite a lot of damage and most of the pads have come off, my question is is this repairable or has too much been taken to create a reasonable circuit?

I would really, really like to get this one working as it's one of the later 33Mhz Alpha's and could turn this into my main machine and keep my present one for backup/spares.
Alex

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Re: A5000 CMOS Replacement

Post by johnkenyon » Mon Feb 13, 2012 4:36 pm

Stupid question, but for tidiness, isn't the A5000 RTC circuit (IC, battery, + crystal) a candidate for moving lock stock and barrel to a small separate PCB with 4 wires (+5v, 0v, SDA, SCL) connected somewhere convenient on the PCB?

ISTR that all 4 are present on the podule port...

/John

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paulv
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Re: A5000 CMOS Replacement

Post by paulv » Mon Feb 13, 2012 5:02 pm

Given my recent success, I'd have a crack at it.

I think in your particular case, the damage looks worse that the one I just repaired and I'd probably opt for a small daughter board to replicate the RTC circuit as John suggests.

Paul

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nOmArch
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Re: A5000 CMOS Replacement

Post by nOmArch » Mon Feb 13, 2012 6:13 pm

paulv wrote:Given my recent success, I'd have a crack at it.
Righto long as it's salvageable I'll give it a go.
I think in your particular case, the damage looks worse that the one I just repaired
Really?!? OK I suppose that bodes well :)
and I'd probably opt for a small daughter board to replicate the RTC circuit as John suggests.

Paul
Woah there hold your horses big fella, this is the guy that had a problem re-soldering the mouse port fuse back in, I think I'll stick with crawling before I try flying! :)
Alex

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TheCorfiot
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Re: A5000 CMOS Replacement

Post by TheCorfiot » Mon Feb 13, 2012 6:16 pm

That is so doable for sure, all the connection points you need are right there, break out the awg30 and go for it my friend.
Nice and slowly and lots of patience.
:D

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paulv
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Re: A5000 CMOS Replacement

Post by paulv » Mon Feb 13, 2012 7:43 pm

Ok, if you're wanting to fix it on the PCB... other things you'll need to check and things I did to make life easier are:

CHECK:

The track that goes from the through hole solder point just above R281 and heads off under the IDE connector actually connects to one of the floppy disc connector pins so you need to check continuity there as I suspect that track is totally gone on your PCB.

There's a very small track between the through hole solder point to the left of R272 and R272 itself. mine had gone and you can't see the wire I used to fix it in the photo's as it's under the others.

You'll also need to check the resistance on the R272 and R281 to make sure they're OK and re-usable.

Pads 1,3 and 4 look ok(ish) check the continuity on them though. Pad 1 to the RHS of C142 and Pads 3 and 4 to the through hole solder point just below them which is a ground point.

Judging by the extra white wires, the connections to the battery have been destroyed. Where do they go, from the -ve side of the battery to earth, it should go through R301 pictured but appears not to. Check the resistance of R301 and if it's good then I'd remove those white wires and re-construct the original tracks.

Check for leakage further down the PCB. The gunk made it all the way down to the ARM3 chip on mine...

TIPS:

You have a lot less solder pads intact than I had so you'll have to think laterally to get the chip soldered down correctly.

Use the through hole solder points to connect your new wiring together as it makes for easier handling of the hookup wire because it's so fine.

Use as fine a point soldering iron as you can lay your hands on. My iron tip is pointy but I still found it a but too big for easy working with the SMT chip and wiring.

Try to avoid using a solder sucker, use solder wick instead. It's fiddly but more gentle and can make a tidier job of it.

HTH

Paul

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nOmArch
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Re: A5000 CMOS Replacement

Post by nOmArch » Mon Feb 13, 2012 9:00 pm

Thank you Paul that's fantastic I feel like I have a slim chance of actually fixing this now, i should have some spare time some evening next week so I will strip down the motherboard and have a good look at the state of the rest of it.

So shopping list so far is

AWG30 wire
Solder Wick
Vinegar/Iso
extra value bag of luck
Alex

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Re: A5000 CMOS Replacement

Post by 1024MAK » Tue Feb 14, 2012 12:41 am

If you don't fancy playing with putting a surface mount chip back on your main board, you could solder a DIL version of the chip to a piece of stripboard (maybe along with some of the other components). Then run wires from good connection points on the main board to the stripboard. Just remember to cut the tracks on the stripboard between the pins on the two sides of the chip :mrgreen:

Mark

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paulv
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Re: A5000 CMOS Replacement

Post by paulv » Tue Feb 14, 2012 12:43 am

Adding to your shopping list, use some proper tip tinner and cleaner. It is so much easier if your soldering iron tips are in good order :D

Something like this does the trick...

http://www.maplin.co.uk/tip-tinner-cleaner-3929

Paul

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AndyF
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Re: A5000 CMOS Replacement

Post by AndyF » Tue Feb 14, 2012 10:07 am

I think either RS or Farnell had them in last time I wanted one, they were not that much money either really. I think I brought three expecting to damage one during fitting and have one spare etc, although no idea where the unused spare is now...
Andy

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nOmArch
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Re: A5000 CMOS Replacement

Post by nOmArch » Tue Feb 14, 2012 11:58 am

You mention small tips, would it be worth investing in something like this?

http://www.ebay.co.uk/itm/Metcal-Hot-Ai ... 35b978036f
Alex

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paulv
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Re: A5000 CMOS Replacement

Post by paulv » Tue Feb 14, 2012 12:52 pm

nOmArch wrote:You mention small tips, would it be worth investing in something like this?
Sadly, I'm not the one to be asking about soldering irons in general.

My usage over the past few years has only been light and I've never gone to the bother of buying an expensive soldering rig as I've never felt that the work I normally do requires it.

To that end, others on the forums are probably better placed to answer that question for you.

All I can say is that my pointy tip felt a shade too big to be 100% accurate with the SMT work.
SolderingTip.jpg
SolderingTip.jpg (25.74 KiB) Viewed 3221 times
Paul

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nOmArch
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Re: A5000 CMOS Replacement

Post by nOmArch » Wed Feb 15, 2012 2:47 pm

Had a spare few minutes so decided to have a look at the mobo.

White wire is soldered to the point derectly underneath the battery

Image

Apart from CMOS looks in pretty good nick.

Image
Alex

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Re: A5000 CMOS Replacement

Post by jgharston » Wed Feb 15, 2012 7:11 pm

My standard recommendation regarding loosing CMOS settings: When you've got the machine configured how you like it, save the setting to disk *SaveCMOS (pathname) so if the settings get forgotten or messed about with a quick R-Power-On and then *LoadCMOS (patname) returns everything to normal.
I save the settings inside !Boot and also have an obey file in there:

Code: Select all

|>!Boot.ReloadCMOS
LoadCMOS <Obey$Dir>.Configure
SyncTime

Code: Select all

$ bbcbasic
PDP11 BBC BASIC IV Version 0.32
(C) Copyright J.G.Harston 1989,2005-2020
>_

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paulv
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Re: A5000 CMOS Replacement

Post by paulv » Wed Feb 15, 2012 7:28 pm

nOmArch wrote:White wire is soldered to the point derectly underneath the battery
Looks to me like there was no need for that. The tracks appear intact on the underside so the secondary hole for the -ve terminal could have been used to seat the battery without having to add any extra wires at all. I'd remove that battery, gently reset the pins or get a new battery and then re-seat it as it should be without the extra wiring :D

Then it should "just" be a case of reconstructing the tracks with some Kynar wire :D

In fact, thinking about it... To give you more space and make life easier, remove the battery, fix the circuit and test and then re-fit the battery once everything else is working as it should be...


Paul

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nOmArch
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Re: A5000 CMOS Replacement

Post by nOmArch » Tue Mar 27, 2012 9:12 pm

OK this is definitely beyond my soldering skills and my buddy is too busy at the moment to take a look.

So I'm looking for someone who is a bit handy with a soldering iron, I could pay £30-£40 also if it's resurrected I will be needing to get rid of my standard A5000 for which I'll be asking the price of repair of the CMOS chip (if that makes sense)

Or I could offer my working A5000 as a straight swap.

Just to be clear I would be removing the IDE Card and other upgrades I've made to it though, you would get a perfect working order A5000 that was refurbished by Mark.

Any takers?
Alex

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Re: A5000 CMOS Replacement

Post by paulv » Tue Mar 27, 2012 10:07 pm

Hmmmm... PM'd you :D

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Re: A5000 CMOS Replacement

Post by TheCorfiot » Tue Mar 27, 2012 10:54 pm

Alex

I'm not that far from you based in mid glamorgan, if paul can't help and you fancy bringing her over I can solder the new chip on for you.

Regards
TC

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Re: A5000 CMOS Replacement

Post by nOmArch » Tue Mar 27, 2012 11:00 pm

Thanks for the offer :) but Paul is gonna have a go at it for the moment.
Alex

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Re: A5000 CMOS Replacement

Post by paulv » Sat Mar 31, 2012 12:47 pm

Well, stage one is complete. I've cleaned up Alex's board and checked continuity. There's actually a reflection in the lacquer now :D

The images are reasonably high res. if you open them up in a new window :D

In the first photo, you can see the tracks quite clearly. All the tracks to the RHS of the 47R resistor are gone. The capacitor C153 also appears to be dead.

The replacement CMOS Alex sent is a through hole type so I've ordered a couple of components and the plan is to build a daughter board with the CMOS chip, X5 crystal and new through hole equivalent of the 15pF C153 cap on.

If I repair the track between R281 (47R) and C154, I can then use four flying leads to connect the daughter board to the motherboard at the existing through hole solder points for power (RHS C154), ground (pins 3 & 4 IC58) and C0 and C1 (pins 5 & 6 IC58).

That's the plan. The daughter board is all mapped out and I'll be soldering up part of that later and removing the crystal X5 from the motherboard in the process.

Image

In the picture below, you can see there's been some damage to the solder pads where the battery attaches. Thankfully, the damage is cosmetic and this part of the circuit seems to be working just fine. While I'm at it though, I'll be replacing the IDE socket :D

Image

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Re: A5000 CMOS Replacement

Post by nOmArch » Sat Mar 31, 2012 1:19 pm

Paul you are a god among men!
Alex

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Re: A5000 CMOS Replacement

Post by paulv » Sat Mar 31, 2012 2:07 pm

nOmArch wrote:Paul you are a god among men!
I wouldn't go that far... LOL

I've done nothing that some IPA a soft bristle toothbrush and some cotton bud swabbing can't sort out yet. Let's wait to see if we can actually make it work again first!

Paul

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Re: A5000 CMOS Replacement

Post by nOmArch » Sat Mar 31, 2012 7:38 pm

New daughter board taking shape nicely
I had a brainwave! You know those old PC sound card to CD player audio cables... Well, I've got tons of them kicking around so this is what I've been up to with one of them...

Here's the component side. I'm missing the socket and 15pF cap. I'll put the socket on later but wanted a shot without so you can see the construction that will be hidden.

The veroboard I've used is in blocks of three rather than in strips as you will see in the bottom photo, so I've used a couple of tinned copper wire (TCW) links which are to the right of the crystal just to bridge two groups of three.

The vertical TCW link will be hidden by the socket once the socket is in place creating a common earth for those two pins as per the circuit.

The yellow hookup wire which is currently unsoldered at the LHS of the board is waiting for the 15pF cap to go in and will link the yellow wire to the top pin of the crystal and pin 1 of the socket which will be in the hole to the right of the top TCW link.
Image

Image
The plan is that once the board is fully soldered and checked as working, I'll attach some double sided sticky backed Velcro and the wire should be long enough for you to place the circuit somewhere safe (probably to the right of the floppy drive somewhere). Using Velcro means that if you need to take the motherboard out later, you can just detach the RTC circuit and pull out the board as normal.
Hat is well and truly off sir!
Alex

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Re: A5000 CMOS Replacement

Post by paulv » Sat Mar 31, 2012 10:18 pm

nOmArch wrote:Hat is well and truly off sir!
Thanks :D I just hope it'll work though. That's the important bit :lol:

I've replaced the IDE socket now and repaired the track needed to provide the last solder point for the "umbilical" as I'm calling it.

Image

... here's the solder side ...

Image

You can see the through hole solder points are all ready for the wiring to be connected and soldered in for the "umbilical" and then once the cap arrives for the daughter board, we should be good to go :D

The CD audio cable makes for a very neat solution to the problem of four flying leads to the daughter board. I have to say I'm pleased with the way things are progressing :D

Paul

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Re: A5000 CMOS Replacement

Post by paulv » Mon Apr 02, 2012 2:50 pm

Ok, here we are then, the moment of truth!

The RTC/CMOS circuit completed and tested for continuity/shorts etc...

Image

The battery replaced and motherboard fitted to my A5000 case ready to be powered on... [-o<

Image

...and finally...

Image

A working A5000 33MHz with 4MB of RAM!

=D> =D> =D>

I'm soak testing for a few hours to check that the battery is charging which it appears to be but it was pretty much fully discharged so that'll be a while yet. I also need to check the IDE socket for full operation and I'm going to stick an Econet module in there for good measure so I can test that too...

On the whole though. It's looking up :D

Paul

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Re: A5000 CMOS Replacement

Post by nOmArch » Mon Apr 02, 2012 3:17 pm

WOOT!

Image

Those pics are a little pot of sheer joy! Fantastic job mate =D> 8)
Alex

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Re: A5000 CMOS Replacement

Post by paulv » Mon Apr 02, 2012 3:28 pm

nOmArch wrote:Those pics are a little pot of sheer joy! Fantastic job mate =D> 8)
You're very welcome :D I'm going to let the battery charge for 5 or 6 hours before I even attempt to power it down now so I can check to make sure it's keeping time and retaining the CMOS settings. The battery was reading 0.75V when I fitted it and now it's reading 3.88V and slowly climbing so it's looking like it's behaving just like mine in the other A5000 thread :D

I'd like to keep the board for another 24 hours before I box it up and send it back to you just to be sure that everything is working as it should.

Paul

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Re: A5000 CMOS Replacement

Post by paulv » Mon Apr 02, 2012 6:45 pm

I couldn't wait the 5 or 6 hours and the battery had reached around 3.95V so I figured I'd power down, fit my IDE CF card and spare Econet module and see what happened.

Around 10 minutes later I powered the A5000 back up and it had retained its settings just fine and kept perfect time too :D

I re-configured the machine to boot from the CF card. Which it did without a hitch and I was able to access the Econet and read floppy discs too so as far as I can tell, everything else on the board seems to be just fine :D

More soak testing this evening and keeping an eye on that battery charge rate before I power it down for a longer CMOS retention test overnight. If everything is working in the morning, I'll leave it on all day to further charge the battery and then post it back first thing Wednesday 8)

EDIT: I should add, now I've got my system drive in there, !ArmSI reports 17.02 MIPS so it's definitely running at the quoted 33MHz... It screams along :D

Paul

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Re: A5000 CMOS Replacement

Post by retroclinic » Mon Apr 02, 2012 7:10 pm

Just to put a slight dampner on your great work - A5000 + CF cards don't mix very well, at least from my experience. I've tried it a couple of times, and I've had data corruption and broken directories on several occations. The ones that work best are the IDE - SD adaptors, they're also faster (for some strange reason).

Mark.
Image

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Re: A5000 CMOS Replacement

Post by paulv » Mon Apr 02, 2012 7:51 pm

Just to put a slight dampner on your great work - A5000 + CF cards don't mix very well
Thanks for the heads up.

I've been running mine with the CF card for about 6 weeks now and it's been fine. I'm using a SanDisk Ultra II card and I know some CF cards don't implement the IDE protocol quite right but at the moment, it does seem to be OK. I'll keep an eye on it though now you've mentioned it :D

Paul

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