New Varta Battery not holding CMOS settings on A3010

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KarateEd
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New Varta Battery not holding CMOS settings on A3010

Post by KarateEd » Sat Dec 03, 2016 8:40 pm

Hi Folks,

I installed the Varta battery some time ago, gave it lots of opportunity to charge up and made some *configuration changes which included !Boot, LCDMode, and monitor settings.

I can shutdown my A3010 and power off, then power on. The setting seems to stick for the *configure settings but not the LCDMode stuff. I think maybe I haven't set up the !Boot file correctly.

Having said that, if I leave the computer off overnight, and I always do, then the settings are lost. It will boot into supervisor mode instead of WimpMode.

Now the question..... shouldn't the Varta battery preserve the CMOS settings and does it need any diode/resister added to the circuit. I would have thought that wires direct from the battery to the old location on the motherboard would have been sufficient to make it work as the original did.

Am I missing something here>

Thanks for any help you can give.

Ed...... :-)
Ed...... :-)

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Re: New Varta Battery not holding CMOS settings on A3010

Post by 1024MAK » Sat Dec 03, 2016 8:48 pm

Yes, the cell (if it's rated at 1.2V) / battery should supply the Real Time Clock (CMOS) chip so that the clock can still function and the SRAM contained inside can remember any data stored in it.

Do you have a multimeter? If yes, measure the voltage between the cell / battery terminals, with the mains power off. Then again with the computer switched on. Do the same test again after the computer has been on for one hour. The report back your results.

Oh, and all the required components are already on the PCB. The question is, which one is faulty, or is there a damaged track...

Mark

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Re: New Varta Battery not holding CMOS settings on A3010

Post by KarateEd » Sat Dec 03, 2016 8:54 pm

1024MAK wrote:Yes, the cell (if it's rated at 1.2V) / battery should supply the Real Time Clock (CMOS) chip so that the clock can still function and the SRAM contained inside can remember any data stored in it.

Do you have a multimeter? If yes, measure the voltage between the cell / battery terminals, with the mains power off. Then again with the computer switched on. Do the same test again after the computer has been on for one hour. The report back your results.

Oh, and all the required components are already on the PCB. The question is, which one is faulty, or is there a damaged track...

Mark
I kind of thought that.... ok, haven't take the machine apart yet (this will be the 4th time since last night) but here's what I'm using for a battery. Also, I'm assuming the measurements you want are between the positive and negative of the battery, correct?
1xBattery.JPG
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Re: New Varta Battery not holding CMOS settings on A3010

Post by 1024MAK » Sun Dec 04, 2016 1:44 am

Yes, between the battery + and -

Mark

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Re: New Varta Battery not holding CMOS settings on A3010

Post by KarateEd » Sun Dec 04, 2016 5:21 am

Hi Mark,

ok, have the one hour or over measures - 3.77 V whether power on the computer is on or off.

I'll have to let it be off over night to get the other measurements.

I'm suspecting it's not the battery though because after I took it apart to get to the battery and put it back together, it came up in supervisor mode again..... leads me to believe the problem is other than the battery.

I will put up the other measurements in about 12 or 13 hours.

Ed...... :-)
Ed...... :-)

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Re: New Varta Battery not holding CMOS settings on A3010

Post by KarateEd » Sun Dec 04, 2016 6:17 pm

Ok, just measured the battery after 9 hours of computer being off.....

3.76 for off and 3.76 after switching on. Of course the CMOS settings have been lost.... :shock: :roll: :lol:

So, from this I conclude that it's not the battery's fault, would that be a correct assumption and if so, what's my next step of investigative troubleshooting?

Thanks guys,

Ed...... :-)
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Re: New Varta Battery not holding CMOS settings on A3010

Post by 1024MAK » Sun Dec 04, 2016 7:07 pm

It is likely that the voltage (and therefore the supply current) is not getting to the CMOS RTC chip. Either there is a broken PCB track, a damaged or missing resistor, or it's possible that the chip is faulty.

If you have steady hands, with the computer off, see if you can find the battery voltage on the power pin of the chip.

Mark

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Re: New Varta Battery not holding CMOS settings on A3010

Post by KarateEd » Sun Dec 04, 2016 8:10 pm

Thanks Mark,

I'll give that a check. I should be able to do this with the computer apart and off, right, since the battery voltage seems to be solid?

Guess I will have to trace back to the CMOS chip also, not sure which one it is......

Ed...... :-)
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Re: New Varta Battery not holding CMOS settings on A3010

Post by danielj » Sun Dec 04, 2016 8:12 pm


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Re: New Varta Battery not holding CMOS settings on A3010

Post by KarateEd » Sun Dec 04, 2016 8:15 pm

Thanks Daniel,

Just to ensure I'm looking at the right thing, is the attached the correct diagram?

Ed...... :-)
Battery Backed RAM-RTC.png
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Re: New Varta Battery not holding CMOS settings on A3010

Post by KarateEd » Sun Dec 04, 2016 9:08 pm

Ok, so if I'm looking at the right thing, on the 'east' side of R60 I get 3.77V so tracks are good up to there.

On the 'east' side of R60 I get between -2 and -5V, minus voltage? Anyway that's a 180 ohm resister so should be something a bit more significant than that I would think.

Also, on R61 I'm getting around 0V on both sides of the resistor. This resistor reads 46.1 ohms. R60 however reads 0 ohms. Bad R60? The track up to R60 is good, I've verified that via voltage and resistance.

Ed...... :-)
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Re: New Varta Battery not holding CMOS settings on A3010

Post by 1024MAK » Sun Dec 04, 2016 11:17 pm

With the meter switched to DC Voltage, connect your negative (black) lead to any convenient 0V / Ground connection.
Then, using the positive (red) lead with a probe, the 3.77V (or so) battery voltage should be present at both sides of R60, R61, and pin 5 of IC5 (PCF8583 CMOS RTC chip).

Now, connect the red lead to the battery positive terminal. Then using the black meter lead, test on both sides of R73, then test on pin 3 and then pin 4 of IC5.

The resistance of R60, R61 and R73 is not critical, but they should be within 5% of their specified values. When testing resistance, always do this test with the power switched off, and the meter leads across the resistor being tested. Because this circuit has a battery in it, the battery as well as any capacitors fed by the battery will have a charge (voltage). This can lead to the meter getting "confused" and giving incorrect results.

Mark

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Re: New Varta Battery not holding CMOS settings on A3010

Post by 1024MAK » Sun Dec 04, 2016 11:25 pm

KarateEd wrote:Ok, so if I'm looking at the right thing, on the 'east' side of R60 I get 3.77V so tracks are good up to there.
Good :-)
KarateEd wrote:On the 'east' side of R60 I get between -2 and -5V, minus voltage?
:?
KarateEd wrote:Also, on R61 I'm getting around 0V on both sides of the resistor.
:( Should have around 3.77V here.
KarateEd wrote: This resistor reads 46.1 ohms.
:D
KarateEd wrote:R60 however reads 0 ohms.
Do you mean ZERO ohms (short circuit) or do you mean the meter is indicating Over-range, meaning infinity (check your multimeter manual if not sure, but is the same display as when the leads are not connected to a resistor) - that is, open circuit? :?:
KarateEd wrote:The track up to R60 is good, I've verified that via voltage and resistance.
:D

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Re: New Varta Battery not holding CMOS settings on A3010

Post by KarateEd » Mon Dec 05, 2016 12:37 am

1024MAK wrote:
KarateEd wrote:Ok, so if I'm looking at the right thing, on the 'east' side of R60 I get 3.77V so tracks are good up to there.
Good :-)
KarateEd wrote:On the 'east' side of R60 I get between -2 and -5V, minus voltage?
:?
KarateEd wrote:Also, on R61 I'm getting around 0V on both sides of the resistor.
:( Should have around 3.77V here.
KarateEd wrote: This resistor reads 46.1 ohms.
:D
KarateEd wrote:R60 however reads 0 ohms.
Do you mean ZERO ohms (short circuit) or do you mean the meter is indicating Over-range, meaning infinity (check your multimeter manual if not sure, but is the same display as when the leads are not connected to a resistor) - that is, open circuit? :?:
KarateEd wrote:The track up to R60 is good, I've verified that via voltage and resistance.
:D

Mark
East for 2nd R60 should be West so West side of R60 is 0.02xV, bounces around a bit, almost no voltage. Still 3.77 on East side.
I get the same for R61, both sides - around 0.02xV, bouncing up and down a few thousandths. So definitely not infinity or complete break. My meter shows 0L for infinity.

Here's the resistors, chip as accurately as I can get with my 35 year old Fluke multimeter..... I'm not sure why I was getting exactly 0 before, perhaps not a solid enough connection.
Pin tests.jpg
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Re: New Varta Battery not holding CMOS settings on A3010

Post by 1024MAK » Mon Dec 05, 2016 1:03 am

Okay, first off, R60, or one of it's connections are not happy :-(

If you have a camera / camera-phone that can take good, sharp pictures (macro mode maybe), can you take a photo of R60 and post it please.

Second, I had "5" on the brain, the +V pin of IC5 is actually pin 8. Sorry about that :oops: #-o

Third, does R73 test okay on resistance?

If R73 is okay (measures around 180 ohms), AND the replacement battery connections are connected to the battery connections on the PCB where the old battery was, it's safe to replace R60 with a thin bit of wire, say 5A fuse wire (or better, a lower rating of fuse wire).

Mark

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Re: New Varta Battery not holding CMOS settings on A3010

Post by KarateEd » Mon Dec 05, 2016 1:18 am

1024MAK wrote:Okay, first off, R60, or one of it's connections are not happy :-(

If you have a camera / camera-phone that can take good, sharp pictures (macro mode maybe), can you take a photo of R60 and post it please.

Second, I had "5" on the brain, the +V pin of IC5 is actually pin 8. Sorry about that :oops: #-o

Third, does R73 test okay on resistance?

If R73 is okay (measures around 180 ohms), AND the replacement battery connections are connected to the battery connections on the PCB where the old battery was, it's safe to replace R60 with a thin bit of wire, say 5A fuse wire (or better, a lower rating of fuse wire).

Mark
ok, so this is not like desoldering on the Beeb, the discreet components are a lot finer. Are the Arc boards multi layered. If just 2 sided, I can handle the job, if not, do you just solder the fuse wire accross to the 2 points on the existing resistor?

I've never bought fuse wire before, can you actually buy it just as a filament? I've only ever seen wire within the glass fuses but never just the wire, something I probably should know but my education in electronics is far from complete as you may have guessed.

I'll check the resistance on R73 before I do any of that anyway and won't be able to do it today most likely, getting late for you and I've put the machine back together again, against my better judgement. just want to ensure I've not damaged anything.... so far, so good..... and I'm getting some great practise assembling the unit, all parts, including the semi-difficult keyboard flat cable. It's not too difficult once you get the hang of it, though my fingers feel pretty chubby when doing that.

Thanks Mark, it seems we've both come to similar conclusions. What is the role of R73? You didn't have me test it just because you like me testing stuff and that would be interesting to know, education so to speak.

I'll also try to post a decent picture of R60 for you......

Thanks again,

Ed...... :-)
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Re: New Varta Battery not holding CMOS settings on A3010

Post by 1024MAK » Mon Dec 05, 2016 9:28 am

Yes, the PCB on Arc's are multi-layered. The usual problem is the battery leakage has destroyed a track, or a via. But it is also possible that the resistor has been damaged. Clean the area up before trying to solder, and if you have some liquid flux, use that to help with the soldering. If you don't have any flux, apply new solder, as the flux in it will help clean the joint. You can always remove the excess using desoldering braid. Don't use a solder sucker, or it may suck up the resistor! You may be lucky, resoldering the connections may fix the problem if it is just a poor solder joint.

With the type of battery (3.6V) that you have, it does not need both R60 and R73. So it is okay to bypass R60 with a piece of thin wire. It does not have to be fuse wire (which is just thin wire where the "burn out" current is known). Any thin wire will do. I only mentioned fuse wire, as that is all some people have in terms of thin wire.

Yes, just solder the thin wire across to the two points on the existing resistor. If however the problem is a track or a via, you may need to use a longer thin insulated wire to go to the other end of the damaged track, to the next component or connection.

If you don't have any fuse wire, don't worry about buying some. If you have some thin wire, any copper wire that has been tinned (dull silver colour), that will do.

The role of both R60 and R73 is to limit the charging current from the +5V supply rail to the battery to a safe maximum value. These batteries are only designed to be charged with fairly small currents. In theory, you only need a single resistor. It can go either on the positive side, or the negative side of the battery. However, decent manufacturers like to include two separate resistors in case one resistor goes short circuit. Acorn did this, but for some reason, put one on the positive side and one on the negative side of the battery. Electrically it make no difference, as charging current has to flow from the +5V supply (in this case via diode D15) then through R60, then through the battery, then through R73 and then the current flows back to the power supply via the 0V rail.

The circuit that is used when the mains power is off, and the battery is the only thing supplying the CMOS RTC chip is: current flows from the positive battery terminal, through R60, then through R61, to pin 8 of the chip (IC5). It flows through the chip, returning to the 0V rail via pin 4. Then flows out of the 0V rail connection on R73, goes through R73 and back to the battery negative. Yes, that sounds strange, but remember, current has to return to the power source. Diode D15 stops the power from the battery trying to power up the whole computer, as D15 is reverse biased. Because the cathode has a higher voltage than the anode (the +5V side connection has no voltage, as the power supply is off), the diode will not conduct.

If the circuit was built using wire ended components on a simple board, it would be far easier to understand.

Once you have got the circuit working, if resistor R60 is faulty, or one of its connections is, you can if you wish, replace the wire with a wire ended resistor.

I hope I got the level of detail right for you. If not, let me know.

Mark

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Re: New Varta Battery not holding CMOS settings on A3010

Post by KarateEd » Mon Dec 05, 2016 2:06 pm

Excellent explanation,

Thanks Mark,

Ed...... :-)
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Re: New Varta Battery not holding CMOS settings on A3010

Post by KarateEd » Tue Dec 06, 2016 3:20 am

Hi Mark,

This is the best I can get out of the poor camera that I have, it's a cheapo from several years ago....still maybe better than nothing.

Ed...... :-)
DSCF1276.JPG
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Re: New Varta Battery not holding CMOS settings on A3010

Post by KarateEd » Tue Dec 06, 2016 4:31 am

Hi Folks,

Redid the resistor measurements again. R61 and R73 check out fine, well within tolerances, less than 2%. R60 however, either infinity or bounces around like crazy on Mohms.

Checked the voltages again, good up to R60 then tiny measurements after that..... suspect R60

Also checked Pin 8 of the chip and same thing, very tiny voltages so it's not reaching.

Think I will experiment with a wire across the R60 and see what happens...

Ed...... :-)
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Re: New Varta Battery not holding CMOS settings on A3010

Post by danielj » Tue Dec 06, 2016 5:40 am

Check continuity from r60 to pin 8. If that's OK, replace r60. Don't short it! Resistors are there for a reason!

d.

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Re: New Varta Battery not holding CMOS settings on A3010

Post by KarateEd » Tue Dec 06, 2016 5:47 am

danielj wrote:Check continuity from r60 to pin 8. If that's OK, replace r60. Don't short it! Resistors are there for a reason!

d.
I'm not sure if you read Mark's explanation of the 2 resistors but it makes sense. We really could do without one or the other of those resistors with no ill affect if I understand that correctly. Oh, continuity ended at R60, was good up to it but nothing. Checked it again after putting the wire in and we're good both continuity and voltage wise to pin 8 of the chip.

What I do know is now the BIOS is holding the configuration, that's good. The worst case senario of the resistor is that it might charge the battery a little faster, in this case R73 also protects against that. Now if something goes wrong with R73, yup, could be a problem.

Thanks Daniel,

Ed...... :-)
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Re: New Varta Battery not holding CMOS settings on A3010

Post by danielj » Tue Dec 06, 2016 6:40 am

Ah, ok - all I read was (it was on my phone) "use wire instead of resistor!" - which is a bad idea until you know what it's doing, but you do, so that's OK :) Excellent news on the fix!

d.

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Re: New Varta Battery not holding CMOS settings on A3010

Post by 1024MAK » Tue Dec 06, 2016 7:32 am

Well done there Ed =D>

Now, it can stay with a wire if you are happy. But if not, either replace the resistor with a SMD resistor, or with a small leaded type (125mW or 1/8W or 250mW or 1/4W say). The resistance can be anywhere between 100 ohms and 180 ohms.

Mark

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Re: New Varta Battery not holding CMOS settings on A3010

Post by KarateEd » Tue Dec 06, 2016 1:59 pm

Hi Guys,

I'm pretty happy with the results. Turned the computer on this morning after being off for 7-1/2 hour and the configs are still perfect. It's really the first time it's booted to the desktop after being off for that long since I owned the beast, so yeup, I'm happy. :D :D :D

I may find a resistor to replace the wire but I'll do that some time later, now it's play time.

Now I can figure out how to properly set up the !Boot and !DeskBoot files.... couldn't really accomplish that before.

Thanks to both of you for your support....

Ed...... :-)
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Re: New Varta Battery not holding CMOS settings on A3010

Post by steve3000 » Tue Dec 06, 2016 7:53 pm

Well done - that looks like a great result!

I guess your original battery must have leaked quite badly and corrosion crept inside the resistor? Whatever the case, it's brilliant to see another mezzaine A3010 saved :)

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Re: New Varta Battery not holding CMOS settings on A3010

Post by KarateEd » Wed Dec 07, 2016 2:27 am

steve3000 wrote:Well done - that looks like a great result!

I guess your original battery must have leaked quite badly and corrosion crept inside the resistor? Whatever the case, it's brilliant to see another mezzaine A3010 saved :)
I didn't see any sign of leakage there but it's certainly possible. It's right in the vincinity.

Ed...... :-)
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