CMOS Battery Replacement Questions

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

Postby pollito » Sat May 20, 2017 7:28 pm

All done and so far so good! The RiscPC remembers the time and CMOS settings. :D :D :D

I just wanted to thank you guys so much. It's always a bit nerve wracking when you are doing things blind, so I'm very grateful for all the handholding.

Thanks again!
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danielj
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Re: CMOS Battery Replacement Questions

Postby danielj » Sat May 20, 2017 7:45 pm

=D> Another RiscPC lives to fight another day! Well done! :)

d.

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Re: CMOS Battery Replacement Questions

Postby 1024MAK » Sat May 20, 2017 8:51 pm

danielj wrote:=D> Another RiscPC lives to fight another day! Well done! :)

What he said =D>

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Re: CMOS Battery Replacement Questions

Postby YuT666 » Sun May 21, 2017 2:20 pm

=D>
Libera Te Ex Inferis ...

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pollito
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Re: CMOS Battery Replacement Questions

Postby pollito » Thu May 25, 2017 8:54 pm

So ... maybe I spoke a bit too soon. :wink:

Actually everything seems to be fine - I can set the time and date, set the number of CD ROM drives, the resolution, etc. and RISC OS remembers this when I power off the computer, even if I unplug the mains lead.

However, if I leave the RiscPC switched off for a couple of days and then power it on again, it gives me the error Error: DataAbort:Abort on data transfer at &03AC0CF4 (&80000002) and leaves me at the * prompt. A quick check and it's the 1st January 1980 again, and I have no CD-ROM drive. I have to power cycle the computer with the DELETE key held down, and set everything up again.

I checked the battery voltage with my newfangled digital multimeter and it read 1.16V. Is this a possible cause? I've already ordered an AAA battery holder from China, which I planned to do anyway (as I was getting tired unsoldering and resoldering the battery wires), but it won't arrive for around a month. When it does, I will fit it with a new rechargeable 1.2V battery.

Any thoughts, as always, would be greatly appreciated. :D
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danielj
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Re: CMOS Battery Replacement Questions

Postby danielj » Thu May 25, 2017 9:01 pm

What sort of battery are you currently using?

If it's an AA, I'd suggest something like an eneloop. The other thing is to make sure it's fully charged!

d.

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Re: CMOS Battery Replacement Questions

Postby Zarchos » Thu May 25, 2017 9:26 pm

The CMOS chip will be happy with up to 5 volts.
1.xx V is really the minimal.
No surprise the 1st Archies had a battery holder for TWO 1.5 V batteries ...
Conclusion : try 2 batteries in a dual battery holder ;-)

You could also try this from Amigakit :
http://amigakit.leamancomputing.com/cat ... ts_id=1093
I used that for the A3000 I modded with a Burr-Brown OPA and it works a treat.
viewtopic.php?f=16&t=11287&hilit=burr+brown&start=30#p142527
The CR2032 is a long lasting 3V non rechargeable battery.

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pollito
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Re: CMOS Battery Replacement Questions

Postby pollito » Thu May 25, 2017 9:53 pm

Daniel: I'm using a battery I bought from APDL around 4 years ago. It has nice long wires and the battery itself is in a sealed rubber sleeve with a piece of double sided tape. It lives at the front of the RiscPC, far away from the motherboard. I'm not sure how I would fully charge it other than to leave the machine on for a few hours. I'm planning on replacing it with the battery holder + 1x AAA rechargeable. I will see if there is an eneloop in AAA size.

Zarchos: I had no idea it could take up to 5V. If the new single battery holder doesn't do the job I will definitely try a dual battery holder or a CR2032. Thanks for that!
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Re: CMOS Battery Replacement Questions

Postby Zarchos » Thu May 25, 2017 10:06 pm

In fact reading this :
http://www.nxp.com/documents/data_sheet/PCF8583.pdf
it appears up to 6V is ok.
1V is the least you can feed it with.

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Re: CMOS Battery Replacement Questions

Postby Zarchos » Fri May 26, 2017 6:00 am

Re reading the thread, I don't know if you did it but I advise you to remove the DRAM and VRAM modules, clean them with a special spray for electronic contacts, do the same to the sockets (see how close they are to the battery and you had leakage in that area), let dry, and put back everything in place.
When aging the RPCs are very difficult with the RAM.
I experienced that issue with a recently bought RPC : no VRAM and only 64 Mbytes of DRAM at 1st, when in fact it had 2 Mbytes and 128 Mbytes.

I don't think it relates to the issue you've got now (CMOS chip) but well just to let you know it's not a bad idea to service the RPC this way.

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1024MAK
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Re: CMOS Battery Replacement Questions

Postby 1024MAK » Fri May 26, 2017 9:10 am

pollito wrote:I checked the battery voltage with my newfangled digital multimeter and it read 1.16V. Is this a possible cause?
Was this voltage measured when the computer was switched off, or when switched on?

The nominal voltage on a single NiCad or NiMH cell when part charged and not connected to a circuit is between 1.1V and 1.2V approx. If the cell has recently been fully charged, the voltage can be between 1.2V and 1.4V depending on how long since the charging stopped.

A NiCad or NiMH cell is considered to be discharged when the voltage drops to 0.9V. But in this circuit we don't want the voltage to drop below 1V, as 1V is the minumum required for the RTC chip to maintain the time and it's memory contents.

However, other than that described above, the cell voltage for NiCad or NiMH cells is not a good indicator of the state of charge. So it's not possible to say if a part charged cell is at 25%, or 75%.

It is best to charge the cell up in a normal charger (if you have one that can do single cells) first. If you don't have a suitable charger, or don't want to remove it from the computer, instead you can leave the computer switched on for more than 48 hours. It does not have to be continuously on. It can be on for say 8 hours each day, for at least 6 days in a row. Depending on the capacity of the cell, even this may not be a full charge. But it should be enough to see if the circuit and cell are working properly.

The other thing is that it is possible that your cell has degraded due to its age. If you have a charger that can charge single cells, you could charge it, then discharge it a couple of times. This "exercising" may help the cell, and it will tell you the condition of the cell (actual capacity).

In this application it is best to use a cell that has a low self discharge characteristic. Most suppliers sell cells where the aim is a large capacity. These have high self discharge rates and are not very suitable.

As Daniel says, Eneloop or similar cells are more suitable.

Mark
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Re: CMOS Battery Replacement Questions

Postby pollito » Fri May 26, 2017 10:16 am

Zarchos: Both the VRAM and RAM are refurbs so they were already shiny. The contacts also looked good when I replaced the old chips with the new ones.

I'm not sure why the battery voltage would be a problem if the original RiscPC battery was 1.2V. Having said that, the original battery leaked all over the board so I guess the machine wasn't without a few design flaws. :wink:

Mark: I measured the voltage with the machine turned off. It's not really possible to discharge and then charge the cell as it is sealed. I don't know exactly what is inside the rubber sheath, between the blobs of hot glue, but I suspect it is a single AAA with a wire soldered to each end. It may well be one of the higher capacity cells. I know that batteries can lose charge over time but it was bought in 2013 and hasn't been used (because of the problem with the battery circuit before). I will check to see which battery it is (as I intend to replace it with a battery holder anyway) and if it is worth keeping I will charge it by leaving the machine on as you suggest. My girlfriend is going to go nuts though as the fan is noisy as hell (that's my next job!).

Many thanks. :)
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Re: CMOS Battery Replacement Questions

Postby pollito » Sat Jun 17, 2017 12:21 pm

The AAA battery holder I ordered from China still hasn't arrived. So in the mean time I have been leaving the RiscPC on for a few hours a day as Mark suggested.

I installed something using PackMan and after the next reboot the RiscPC refused to remember the time, CD-ROM drives, ethernet settings, etc.

Even if I set the time and date while the machine is running, it changes itself to a date in 2004, and changes to the BIOS do not survive a reboot.

When booting the screen flashes red and it gives me an error, for a split second, about the CMOS settings for the ethernet card.

I have measured the battery and it now reads 1.35V so it looks as if it is being charged.

Any ideas? I've tried holding DEL while turning the machine on (and R as well). It looks like I'm back to square 1. :(
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Re: CMOS Battery Replacement Questions

Postby danielj » Sat Jun 17, 2017 12:29 pm

When it's off, do you see a voltage back out of the battery? (or is that when you're reading the 1.35v?) And are you reading a voltage on the relevant pin of the CMOS IC?

d.

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Re: CMOS Battery Replacement Questions

Postby pollito » Sat Jun 17, 2017 1:05 pm

Hi Daniel.

Thanks for your reply.

It's 1.35V when the machine is off. I checked the voltage between the pins where I initially checked the resistance for 180 ohms.

Incidentally I checked the resistance again and although the resistance between the negative terminal and the IC20 chip measures around 179 ohms, the replacement resistor I fitted between the positive terminal and D2 only reads 177 ohms. Do you think this would make any difference?

It's weird how it's been working for the last couple of weeks without any issue. Could it have been a software thing corrupting the CMOS? Is it worth disconnecting the battery for a couple of days or even reinstalling the OSes?
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Re: CMOS Battery Replacement Questions

Postby danielj » Sat Jun 17, 2017 2:41 pm

It's a 180ohm resistor, so 179 or 177 is still within a 2% tolerance - I very much doubt it'd make any difference. Double check the continuity of all the connections of the CMOS IC. If it's still misbehaving, replacing that might be the solution :? (I don't think it's likely to be a software issue)

d.

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Re: CMOS Battery Replacement Questions

Postby flaxcottage » Sat Jun 17, 2017 3:08 pm

I had this trouble with AA cells. Absolutely naff at holding charge. In the end I swapped them for a Varta 3.6v 150mAH battery pack and never looked back. I use these in all my ARM machines.
- John

Currently running Level 4 Econet with BBC B, BBC B+ 128K, Master 128K, 4Mb A3000, 4Mb A3020, 4Mb A4000, 4Mb A5000 dual FDD; UK101; HP41CX setup; Psion 3a, 3mx and 5mx; Z88; TI-58c, TI-59 and printer, HP-16C programmer's calculator

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Re: CMOS Battery Replacement Questions

Postby pollito » Sat Jun 17, 2017 3:29 pm

Daniel: I don't know how to do that, I'm afraid. And I have no idea where I could get a replacement IC20 chip from.

To be honest, soldering that resistor into place took me a lot of time. I don't know if I have the required skill to solder a replacement chip in place.

John: I'm not sure how this would explain how it was working before and now it isn't. Is the RiscPC capable of keeping such a large battery charged? I wonder if there's an easy way of testing whether a higher voltage battery would resolve the issue before investing in one of those Vartas.
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Re: CMOS Battery Replacement Questions

Postby danielj » Sat Jun 17, 2017 4:00 pm

How are you with reading the schematic? What you basically need to do is check that each of the lines coming from the CMOS IC is connected to what it's meant to be connected to.

Replacing the IC is a little trickier if it comes to that - do you know anyone with a hot-air solder rework station? The IC itself is fairly easy to source.

d.

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Re: CMOS Battery Replacement Questions

Postby pollito » Sat Jun 17, 2017 5:30 pm

I had a close look and noticed that there was some gunk between two of the pins of IC20. I put some isopropyl alcohol on a cotton bud and wet in-between the pins. I then used a needle to scrape away the gunk, wiped again with more alcohol and let it dry. My RiscPC now seems to remember the CMOS settings after both a reboot and a power cycle. :D

Just in case I have ordered one of the Varta 3.6V 150mA batteries from RS UK and will pick it up from my parents' house in a couple of weeks when I'm back in Bath. After this saga I really don't want any more CMOS or battery problems!!

Many thanks for your help, both of you. I'm glad I haven't (yet) had to change the IC itself. I don't know anyone here apart from me who owns a soldering iron, let alone a hot-air solder rework station!
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Re: CMOS Battery Replacement Questions

Postby danielj » Sat Jun 17, 2017 5:35 pm

Great work :) =D>

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Re: CMOS Battery Replacement Questions

Postby flaxcottage » Sat Jun 17, 2017 6:54 pm

Excellent. :D 8)
- John

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Re: CMOS Battery Replacement Questions

Postby Zarchos » Sat Jun 17, 2017 6:59 pm

Very good news indeed !

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Re: CMOS Battery Replacement Questions

Postby SteveF » Tue Jul 11, 2017 6:18 pm

Apologies if this is a thread hijack, I thought it was best to ask here than start a new thread...

Given a machine which has been in storage and suffered CMOS battery leakage, is it safe to turn the machine on *before* doing the vinegar+distilled water cleaning step, to see if it's in working order, or is it important to clean *then* apply power?

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Re: CMOS Battery Replacement Questions

Postby 1024MAK » Tue Jul 11, 2017 9:12 pm

Well...

IMHO, not much in it. Others may disagree.
If I know that there is damage, I prefer to clean it up. But if I don't know / have not taken the case off, yes I power it up...

It's all low voltage circuitry anyway, and in industrial systems, the damage occurs while it's powered on...

Not really helping, I know. But up to you...

Mark
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Re: CMOS Battery Replacement Questions

Postby SteveF » Tue Jul 11, 2017 9:20 pm

No, that's a great answer. I already picked one of the two answers and went ahead and acted on it and now I slightly regret it, but now I can say to myself I did the right thing. Thanks! :-)

(I cleaned the board up without testing it first and it's not working now, so obviously now I wonder if I broke it during cleaning. But I'll assume I didn't, no one can ever prove otherwise. :-) )

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Re: CMOS Battery Replacement Questions

Postby 1024MAK » Tue Jul 11, 2017 11:35 pm

The battery leaking very likely caused PCB track damage, or damage to components/connectors.

The battery leakage would have have had to be cleaned up at some point if you wanted to repair / service it anyway.

Mark
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Re: CMOS Battery Replacement Questions

Postby SteveF » Wed Jul 12, 2017 7:21 pm

Cheers, I'll bust out the multimeter at some point and see if I can find any damage. Plenty of tips in this thread anyway...


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