CMOS Battery Replacement Questions

Arc/RPCs, peripherals, RISCOS operating system & ARM kit eg GP2x, BeagleBoard
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pollito
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CMOS Battery Replacement Questions

Postby pollito » Mon Feb 06, 2017 6:00 pm

Hi there,

Apologies in advance for the noob question. A few years ago I bought a RiscPC from eBay. The seller told me the battery needed changing, hence the CMOS settings weren't saved.

I immediately removed the old CMOS battery and bought a replacement with nice long wires to avoid any future potential battery damage. I soldered the battery leads onto the same connectors as the old one but it still wouldn't save my CMOS.

I have just come back to my project as I'm visiting my parents in the UK and want to send my RiscPC back to Romania.

I am a little confused and was wondering if someone could please have a look at the attached photo and tell me a) if it's soldered correctly (I have no idea why the positive has a loop) and b) if those components around the terminals look like they have been damaged by corrosion.

Many thanks in advance.
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IMG_7998.JPG
Battery connectors
pollito

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danielj
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Re: CMOS Battery Replacement Questions

Postby danielj » Mon Feb 06, 2017 6:48 pm

Slight damage, I'd be tempted to give it a little wash with vinegar then a good rinse in distilled water just to make sure any remaining rubbish is neutralised. Then you need to check that the resistors are resisting and both them and the capacitors are connected where you'd expect them to be.

Technical drawings are here: http://chrisacorns.computinghistory.org ... awings.zip


The loop isn't necessary - it just needs to be attached to one of the +ve pins (unless something's gone terribly wrong!). I'd be tempted to remove the remainder of the pins, clean up the holes and solder the wires into the holes.

Fingers x'd!

d.

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Re: CMOS Battery Replacement Questions

Postby flaxcottage » Mon Feb 06, 2017 10:43 pm

Tomato ketchup also works a treat as an alternative to vinegar if a longer time is needed to "de-green". Mind you it is messier to wash of! :lol:
- John

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pollito
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Re: CMOS Battery Replacement Questions

Postby pollito » Mon Feb 06, 2017 11:01 pm

Many thanks, Guys. I'm leaving the country in a couple of days and don't have white vinegar, distilled water or my multimeter here. So I'll wait until my RiscPC arrives in Romania and give it a go. :)

I'm quite excited now and have ordered 128MB RAM. :) :)

Thanks again,
pollito

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Re: CMOS Battery Replacement Questions

Postby Captain Jack » Sat Feb 18, 2017 7:03 pm

Have exactly the same issue with my *working* motherboard. Replaced battery but all settings are lost, such as time and mouse type (using a serial one). Not a huge deal since I can set the time via NTP and set various options via !Boot but ... would like this working.

There was a little bit of leakage but nothing terrible, which I cleaned up. The diagrams seem to differ slightly around CMOS - my board this 0197,100 while the diags are for 0197,000. The CMOS is shown in the middle of the board (http://www.riscos.info/images/c/c6/RPC_PCB1_C.png) not on the edge, so not sure which resistors/capacitors are which since they are not labelled on the board.

The chip itself does seem to be getting 1.3v when the power is off on pins 5 and 6, though not 8 and I am not sure what it should be - maybe some kind soul can run a multimeter between pin 8 and ground?

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pollito
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Re: CMOS Battery Replacement Questions

Postby pollito » Sat Apr 22, 2017 11:16 am

Hi guys,

I finally got my Risc PC to Romania and started the cleaning process. It has been more than a little unsettling dabbing white vinegar on a board and then washing it off with an alcohol / distilled water mixture. :shock:

I've got a few questions that and would really appreciate it if someone could advise me:

1. After the first time cleaning with vinegar, I waited a few minutes and then poured the solution of 50% water, 50% alcohol onto the affected part of the board. After 24 hours there seemed to be white fuzzy bits on the board and between some of the chips which I gently scraped off with the blunt end of a needle. Is this normal?

2. I could see there were bits of blue/green left so I had another go. This time I had bought a big bottle of isopropyl alcohol. I used this neat (instead of mixing it with the distilled water). Was that okay to do or should I do it again adding the water?

3. I can't seem to get all of the blue/green stuff off and was hoping somebody could tell me if this is a problem or not:

corrosion_small.png
Corrosion


If so what is the best way of removing it? Maybe I'm not leaving the vinegar on for long enough?

4. When I re-solder the battery to the board, which positive terminal should I use? And should I completely remove the bits of metal that are soldered to the - and one of the + terminals?


Thanks again in advance. It's really nice to have some expert advice when doing something like this. I really hope my Risc PC still works when it's back together. #-o
pollito

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Re: CMOS Battery Replacement Questions

Postby Zarchos » Sat Apr 22, 2017 11:42 am

There are more qualified people to answer but with my Archies and RPCs, I don't absolutely try to get a motherboard 'ultraclean' : as long as the vinegar has been poured on and let working for a dozen minutes, to me it's enough.

For the '+' terminals you can choose any : on the other side of the motherboard, they are linked, anyway.

And no don't bother removing the bits : it's more important you make a good soldering, than having a motherboard so nice that you can dream of it at night ... really who cares except purists ... (says the guy who spent hours simply to save 1 cycle here and there in his code ah ah ... self critism is much fun, oops).

Hope this helps !

Xavier.

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Re: CMOS Battery Replacement Questions

Postby vanekp » Sat Apr 22, 2017 11:57 am

I would look very closely at this part of the circuit especial R130 (181 on the board) and R133 (470 on the board) to make sure you have 1.2v going to the cmos chip (IC20)
battery backed ram_rtc.png

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1024MAK
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Re: CMOS Battery Replacement Questions

Postby 1024MAK » Sat Apr 22, 2017 2:00 pm

pollito wrote:1. After the first time cleaning with vinegar, I waited a few minutes and then poured the solution of 50% water, 50% alcohol onto the affected part of the board. After 24 hours there seemed to be white fuzzy bits on the board and between some of the chips which I gently scraped off with the blunt end of a needle. Is this normal?
The idea is to apply white (clear) distilled vinegar to neutralise the leaked battery fluid. Then wash it off with tap water. Then a second wash with distilled water. Then let it dry. Once dry, any grease or similar dirt can be cleaned with IPA (alcohol).

There are a number of causes of white fuzzy stuff.

pollito wrote:2. I could see there were bits of blue/green left so I had another go. This time I had bought a big bottle of isopropyl alcohol. I used this neat (instead of mixing it with the distilled water). Was that okay to do or should I do it again adding the water?

3. I can't seem to get all of the blue/green stuff off and was hoping somebody could tell me if this is a problem or not.
The blue/green stuff is the byproduct of the copper/brass having corroded. A bit like rust on steel. Neither vinegar, water or IPA will remove it on it's own. You need to either carfully scrape it (be VERY gentle on PCB tracks, or they will lift off or break) or use a fibre pencil to clean it off. As long as the board stays dry, and as long as the blue/green deposit does not short across anything, it's safe to leave it there. Just get the worst off.

pollito wrote:4. When I re-solder the battery to the board, which positive terminal should I use? And should I completely remove the bits of metal that are soldered to the - and one of the + terminals?
Do you mean the positive terminal on the battery or the board? On the battery, it does not matter. On the board, if the two positive pads are still linked by a PCB track, it does not mater, otherwise use the pad that has tracks leading from it. Upto you if you want to remove the legs on the board. Some people prefer to solder wires to what is left of the old battery leg. But don't try to solder directly to a new battery, connect to the legs provided by the manufacturer.

Mark
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Re: CMOS Battery Replacement Questions

Postby pollito » Tue Apr 25, 2017 2:45 pm

Hi guys,

Many thanks for all your advice.

I think the thing that everyone seems to agree on is that the acid in the vinegar neutralises the (presumably alkaline) gunk from the battery and, after 10 minutes or so, this needs to be washed off with water or/and isopropyl alcohol.

I used the vinegar, rinsed it off with distilled water and then rinsed it a second time with isopropyl alcohol. That was on Sunday.

It's now Tuesday and the board seems to be dry (it has been above the radiator in the kitchen as I don't have an airing cupboard). Do you think it's okay to reattach the battery and reassemble the machine? Or should I wait longer?

Thanks for the battery advice as well 1024MAK. I'm really looking forward to putting everything back together and am really hoping to hear the familiar start up beep when I do.

Kind regards,
pollito

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danielj
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Re: CMOS Battery Replacement Questions

Postby danielj » Tue Apr 25, 2017 2:55 pm

When I did my A3010 this weekend, it just got overnight (that said there are less bitty connectors around the battery on that) - I'm sure it's fine :)

d.

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Re: CMOS Battery Replacement Questions

Postby 1024MAK » Tue Apr 25, 2017 9:40 pm

Yes, it will be dry, so go ahead and re-assemble :wink:

Mark
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Re: CMOS Battery Replacement Questions

Postby pollito » Sat Apr 29, 2017 11:00 am

Okay so I soldered the CMOS battery to the pins and checked the voltage on the pins underneath the board. Then I put the machine back together and, to my relief, it booted. :D

However I have the same issue as I did before - whenever I power on the machine I get a brief message "Warning: CMOS RAM for EtherM in socket 8 defaulted" and the machine won't remember the time. Telling it to get its time by NTP sets the year to 1949 so I can't even use that as a workaround. :?

I am not good at following electronics diagrams or particularly good at soldering but I would really like to get this working. Where should I start?
pollito

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Re: CMOS Battery Replacement Questions

Postby DutchAcorn » Sat Apr 29, 2017 11:33 am

pollito wrote:Okay so I soldered the CMOS battery to the pins and checked the voltage on the pins underneath the board. Then I put the machine back together and, to my relief, it booted. :D

However I have the same issue as I did before - whenever I power on the machine I get a brief message "Warning: CMOS RAM for EtherM in socket 8 defaulted" and the machine won't remember the time. Telling it to get its time by NTP sets the year to 1949 so I can't even use that as a workaround. :?

I am not good at following electronics diagrams or particularly good at soldering but I would really like to get this working. Where should I start?

Are configuration options retained while the power is on? You can check this by setting an option (e.g. baud), reset, and then check with *status if the option is still set.

If options are retained as long as the computer is switched on, the issue is most likely related to the battery circuit. You can check if the cmos is getting the voltage from the battery by measuring the voltage on pin 8 on the CMOS chip (IC20) when the computer is switched off. You should measure more than 1V between pins 8 and 4 (pin 4 is / should be connected to 0V).

cmos marked.JPG
(22.94 KiB) Not downloaded yet


If the settings are not retained while the computer is switched on the issue is likely to be caused by:
1 Broken tracks to and from the CMOS chips
2 Broken components (e.g. resistors) in the circuit to and from the CMOS chip
3 A faulty CMOS chip

In that order :wink:
Paul

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Re: CMOS Battery Replacement Questions

Postby pollito » Sun Apr 30, 2017 1:45 pm

Hi Paul,

Thank you very much for your reply.

I ran the SaveCMOS utility in RISC OS 6 which appeared to make the network warning go away, and the network settings are being retained. However the screen resolution is not saved, nor are the number of CDROMDrives and, without NTP enabled, the clock seems to jump around like crazy. Occasionally I get this error when I switch on: Error: DataAbort:Abort on data transfer at &03AC0CF4 (Error Number &80000002).

I can set the parameters such as CDROMDrives and these survive a reboot, but not a power cycle. I checked and there is definitely no voltage reaching the CMOS chip when the computer is off. However there is voltage when it is powered on.

What do you think I should do next?
pollito

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danielj
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Re: CMOS Battery Replacement Questions

Postby danielj » Sun Apr 30, 2017 2:09 pm

So, check connection from battery positive to Resistor R130, then check that R130 has a resistance of 180ohms across it, then check connection from R130 to R133 - assuming you're getting 5V to pin 8 of the CMOS IC when it's turned on, then the issue has to be somewhere between the +ve terminal of the battery and where that meets up with the circuit that leads from 5V to pin 8 :)

d.

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Re: CMOS Battery Replacement Questions

Postby DutchAcorn » Sun Apr 30, 2017 8:26 pm

danielj wrote:So, check connection from battery positive to Resistor R130, then check that R130 has a resistance of 180ohms across it, then check connection from R130 to R133 - assuming you're getting 5V to pin 8 of the CMOS IC when it's turned on, then the issue has to be somewhere between the +ve terminal of the battery and where that meets up with the circuit that leads from 5V to pin 8 :)

d.


I concur :D

It can also be the connection of the - terminal. So there are two resistors to check; R212 and R130:
battery backed ram_rtc marked.png


They do not seem to be marked on the PCB. I marked them in the picture below. You can check if the resistors are doing their job by measuring resistance between the battery - terminal and pin 4 of the CMOS chip (for R212) and the resistance between the battery + terminal and diode D2:

corrosion_small RPC marked.jpg


Both should measure 180 Ohms. You don't have to remove the battery to check this.
Paul

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Re: CMOS Battery Replacement Questions

Postby pollito » Sun Apr 30, 2017 9:04 pm

Thanks guys! You are awesome! :D

The verticle (- to the CMOS chip) reading was fine - 180 Ohms, so I guess that R212 is okay. The horizontal one (+ to D2), however, didn't show a reading at all. How should I proceed?
pollito

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Re: CMOS Battery Replacement Questions

Postby danielj » Sun Apr 30, 2017 9:21 pm

Can you check + to the south side of R130? then the north side of R130 to D2?

Did you check the resistance across R130?

d.

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Re: CMOS Battery Replacement Questions

Postby DutchAcorn » Sun Apr 30, 2017 9:37 pm

From your photo it looks as though the track just above R130 has been eaten away. The resistor itself may still be ok.

If that is correct you should be able to measure 180 Ohms between the + terminal and the north part of the resistor, as Daniel suggests ^^

corrosion_small marked2.png



I don't know your soldering skills but you could then solder a small bit of wire between the diode D2 and the north of R130.

corrosion_small marked3.jpg



Alternatively you could use a new 180 Ohms resistor and put that as a bypass between the + terminal of the battery and D2.
Paul

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Re: CMOS Battery Replacement Questions

Postby 1024MAK » Sun Apr 30, 2017 9:38 pm

Measure between the pins of resistor R130. Your meter should read 180 ohms.

Measure between the top most pin of R130 and the pin of the diode (D2) that is arrowed in the photo a few posts above. Your meter should read less than 1 ohms.

Measure between the bottom most pin of R130 and the battery positive terminals (+). Try first one + terminal, then the other + terminal. Your meter should read less than 1 ohms.

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Re: CMOS Battery Replacement Questions

Postby pollito » Mon May 01, 2017 7:21 pm

I am unable to measure the resistance of the R130 resistor (doesn't show anything on the multimeter), nor does there appear to be any connection from the positive terminal to R130, or from R130 to D2. However, the south side of the resistor inbetween R212 and R130 (R133) appears to be connected to D2 fine.

Does this mean I can buy a 180 ohms resistor and solder it between the positive terminal and the top pin of D2?
pollito

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Re: CMOS Battery Replacement Questions

Postby danielj » Mon May 01, 2017 7:40 pm

Yes :) - So, we assume that R130 is dead and the tracks to/from it are gonners. Hook up a normal through hole 180ohm resistor between the +ve battery terminal and D2 - I'd probably cut one lead fairly short, get that well soldered onto the pad of D2, then cut the other lead on the resistor and use a flying wire from the +ve battery terminal to that. Once you've done that, check that you measure 180ohm between the +ve battery terminal and D2 and then check the voltage hitting IC20 :)

(I'd be tempted to remove R130 just in-case too)

d.

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Re: CMOS Battery Replacement Questions

Postby 1024MAK » Mon May 01, 2017 10:25 pm

One thing to be aware of: soldered connections that have suffered corrosion due to battery leakage need carefully cleaning before new solder will "take". I use a fibre pencil, as shown in this thread. Go careful, gentle cleaning, not elbow power is all that is required. And best to avoid breathing in the dust.

The very same corrosion can prevent test probes from making good electrical contact.

Mark
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Re: CMOS Battery Replacement Questions

Postby pollito » Tue May 02, 2017 9:09 am

So this is what we believe is happening, right?

BatteryCircuit.png
(2.2 KiB) Not downloaded yet

Daniel - I have ordered some 180ohm 1/4W through hole resistors. Would they suffice? Also why would you remove R130 if it and it's tracks aren't working? I'm not even sure how I would remove it and am worried about damaging the board.

Mark - I have also ordered a fibre pencil and will use this to double-check my diagnosis once the component contacts are clean. I will double-check everything and let you know if anything is different before I attempt to solder a new resistor from +5V to D2.

EDIT: R130, not R133 - thanks Daniel ;)
Last edited by pollito on Tue May 02, 2017 10:26 am, edited 1 time in total.
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Re: CMOS Battery Replacement Questions

Postby danielj » Tue May 02, 2017 9:16 am

It was really just in-case it was making spurious contacts or slightly conductng or something. Just seems neater to get rid of anything potentially confounding, even if it's extremely unlikely it'll confound :) (it's R130 I'd remove -not R133!)

d.

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Re: CMOS Battery Replacement Questions

Postby 1024MAK » Tue May 02, 2017 9:23 am

pollito wrote:Daniel - I have ordered some 180ohm 1/4W through hole resistors. Would they suffice? Also why would you remove R133 if it and it's tracks aren't working? I'm not even sure how I would remove it and am worried about damaging the board.

Yep, a 180 ohm 1/4W through hole resistor is fine.

The idea behind removing R130 is in case the problem with it, or its connections is intermittent. If both it and the new 180 ohm resistor are both in circuit and both conduct electricity, with the computer powered on it will increase the charging current to the battery. Also leaving it there may confuse someone working on the board in the future.

However, my view is that as I would like you to do a couple of tests once you have had a go at the pads with the fibre pencil, I think we can then determine if it is a track fault, or R130 that is faulty. And as the charging current is low anyway, I do not consider leaving R130 there a risk.

Ahh, Daniel got in first :lol:

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Re: CMOS Battery Replacement Questions

Postby danielj » Tue May 02, 2017 9:28 am

:D
If it's got to the "removing it" stage, it's just a question of getting it fairly hot with a soldering iron across the width of it, and you should be able just to nudge it off its pads gently. Don't force it! Once it's off, you can clean the pads with some desoldering braid.

d.

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Re: CMOS Battery Replacement Questions

Postby pollito » Tue May 16, 2017 7:35 pm

A fibreglass pen from the UK finally arrived and some 180 ohms resistors from France (the pièce de résistance :wink:)

My multimeter died so I had to buy a new one. It's digital and doesn't seem to be as accurate, but it works (which is the important thing)

I spent some time gently rubbing away the years of dirt on either side of R130. As far as I can tell the resistor is dead as is the track between the positive terminal and R130, and also the track between R130 and D2.

So it looks like I'll have to remove R130. The trouble is that finding a chisel-tipped soldering iron here in Romania seems impossible. Can I use the conical one or should I get my dad to send one from the UK, delaying things by another week? I'm really keen to get this fixed.
pollito

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Re: CMOS Battery Replacement Questions

Postby danielj » Tue May 16, 2017 8:31 pm

The other way to do it is to feed enough solder in so it blobs across onto both sides of the resistor, which will then melt both sides, then nudge it off?

d.


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