[HN Gopher] Building a replacement 386/486 CMOS battery
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Building a replacement 386/486 CMOS battery
Author : Brajeshwar
Score : 56 points
Date : 2024-12-23 14:52 UTC (1 days ago)
(HTM) web link (rubenerd.com)
(TXT) w3m dump (rubenerd.com)
| smitelli wrote:
| The only thing worse than these soldered-in batteries are those
| motherboards with the Dallas DS1287 RTC "brick" ICs. They had a
| coin cell buried inside the chip[1] with no way to provide
| external power should it drain.
|
| [1]: http://www.mcamafia.de/mcapage0/dsrework.htm
| alnwlsn wrote:
| The only thing worse than that is when those things are
| soldered and not in a DIP socket. They still make them (or a
| compatible version) by the way, sealed battery and all.
| TeamMCS wrote:
| Ah yes. I've had to repair one of the Dallas ICs before. You
| have to dig out a dremel and bite down till you get to the
| metal then add some hook up wire. Unlike OP I chose to use
| rechargable batteries that used to be used for home wireless
| phones - they are the right voltage and often they supply a
| battery charger.
|
| If you're lucky you can desolder the the old battery and use a
| couple of pin headers to get you back up and running. I do find
| it irritating some retro machines wont even boot without a
| working battery.
| adrianmonk wrote:
| Yeah, those are a thing on old Sun workstations. They have a
| clock and they also store a small amount of data.
|
| https://www.sun3arc.org/FAQ/sun-nvram-hostid.faq.phtml
|
| I remember replacing one in the mid 1990s. The machine's
| ethernet address is stored on this chip, and I believe it's
| battery-backed RAM (not flash, EEPROM, etc.), so when the
| battery dies, the data on the chip is lost.
|
| When you install a new chip, you need to program in the
| ethernet address so the machine can get on the network. The
| proper thing to do is use the factory-assigned ethernet address
| to ensure that it is unique. But you can't get the address from
| the old chip. So, like many people, I just picked some random
| numbers. It worked.
| rzzzt wrote:
| Necroware has a replacement design for Dallas RTCs:
| https://github.com/necroware/nwX287
| hyhconito wrote:
| I don't know why there is a replacement design. You can still
| buy them new from Mouser. They last 20 odd years usually.
| moffkalast wrote:
| Is this some attempt to get around "contains batteries"
| shipping restrictions, since if anyone looks inside it'll just
| be like any other chip and there's no way to tell unless you
| start googling part serials lmao.
|
| "No batteries here, officer! Move along."
| Bluecobra wrote:
| I'm not sure if it's worse, since AFAIK these don't leak. I
| have a IBM PS/2 system that I inherited that I plan to restore
| some day. Sure it's a pain but glad there was no damage to the
| board.
| blueflow wrote:
| Dedication and a cutter knife do it. I did it myself, twice.
|
| Once while it was soldered into a mainboard :P
| userbinator wrote:
| There were lots of test equipment with variants of those, and
| unlike CMOS settings, they held critical calibration constants.
| rasz wrote:
| >no way
|
| you drill/dremel in two spots, solder tow wires and you are
| done.
|
| https://www.classic-computers.org.nz/blog/2009-10-10-renovat...
| geon wrote:
| You can also heat them up, making the resin brittle so you
| can chip it away and replace the battery.
| dhuk_2018 wrote:
| Why not use lithium AA? Duracell aklaleaks are the worse, in my
| experience. At least if the alkalines do leak, they're in a
| carrier away from the MB.
| orev wrote:
| They're using rechargeable NiMh, not alkalines. I would have
| used the older Eneloops or current Fujitsus, but maybe
| rechargeable Duracells have better quality than their
| alkalines.
| winrid wrote:
| The NiMH Duracells are very high quality (at least according
| to Project Farm).
| buildsjets wrote:
| Lots of older Apple hardware used soldered-in 1/2AA lithium
| batteries. You can replace them with a removable battery holder
| that was used on some later board versions.
|
| https://www.mouser.com/ProductDetail/Keystone-Electronics/10...
|
| https://www.mouser.com/ProductDetail/Keystone-Electronics/10...
| hyhconito wrote:
| Just a note with those holders. They shouldn't be used in
| anything that will be shipped as the battery can get knocked
| out. The original shipped batteries were soldered in so they
| could be shipped safely. In fact a lot of the time the cells
| were taped or cable tied as well as soldered in on some bits of
| hardware!
|
| The newer CR2032's have much lower mass and can withstand many
| more G's before it's an issue so they are usually in holders.
| buildsjets wrote:
| That is why I added the second Mouser link for the retaining
| clip, which is frequently missing from old stock. It takes a
| screwdriver to unclip it, plenty secure for transportation.
| hyhconito wrote:
| Got it thanks. That link crashed Mouser the first time so I
| assumed it was a dead one :)
| incanus77 wrote:
| I took this same approach when I repaired a 386 damaged by a
| Varta battery. After fixing some motherboard traces, I installed
| a Velcro's 3xAAA battery holder in my case for the same effect.
|
| https://justinmiller.io/posts/2020/06/17/project-386-part-4/
| jmclnx wrote:
| I actually did the same thing for my old 286 ages ago, worked
| great for many years. Sadly I moved to a smaller place and was
| stupid enough to toss it out :(
|
| Too bad they went to soldered batteries, decades ago people realy
| knew how to design systems in the old days. Now, not so much.
| Suppafly wrote:
| This is cool, but I'm pretty sure you get these off the shelf.
| I've scavenged them from old computers and I doubt people were
| building them themselves.
| gamedna wrote:
| Love this, but iirc this was very common back in the day. Many of
| the XT, AT, 286, 386, 486 clones came with these types of triple
| AA battery packs, some with shrink wrap around them. It was easy
| to cut the shrink wrap and replace the cells with generic AA.
| accrual wrote:
| That's my recollection as well. RTC batteries from this era
| often came in four possible flavors:
|
| * Varta barrel battery, subject to leaking and corroding traces
|
| * AA/AAA style brick + leads to motherboard, easy to replace
|
| * Dallas DS1287 epoxied battery + chip - can be replaced, cut
| into to tap directly into the chip, or replaced with
| Necroware's nwX287 RTC module [0]
|
| * Lastly, the standard CR2023 style. I started seeing these
| appear in later 486 Socket 3 boards, very rarely on anything
| earlier
|
| [0] https://github.com/necroware/nwX287
| ruslan wrote:
| Why not use a 5F/5V supercapacitor, DGH505Q5R5 or anything alike
| ? You may need to solder a 10R current reducing resistor in
| series.
| Denvercoder9 wrote:
| Not OP, but with supercapacitors you're talking about a wildly
| different amount of energy. A 5F/5V cap stores about 62 J,
| while a 2500mAh 1.2V AA battery stores 10 kJ. With three of
| them you can store almost 500x as much energy.
| londons_explore wrote:
| What advantage does a supercap have over batteries?
| Kirby64 wrote:
| Super capacitors have very high self discharge rates relative
| to a lithium battery. For something like an RTC which only uses
| a tiny amount of power, you'd quickly discharge the cap and
| have no way to charge it again.
| johnklos wrote:
| It's good to see this getting some attention. People should know
| that removing batteries and replacing them with something modern,
| particularly non-leaking modern, is a good thing.
|
| Most motherboards work with 3 to 4.5 volts. If a circuit doesn't
| charge, then it's a simple matter of using two or three AA or AAA
| batteries. If it does, we can use rechargeable batteries (I've a
| box of Ikea ones), or we can put a diode in line.
|
| For instance, here's a replacement set for a Quadra 630
| motherboard:
|
| https://www.klos.com/~john/q630_batteries.png
| roytam87 wrote:
| AA or AAA batteries will leak.
| devilbunny wrote:
| If you have enough case space, that's not really a big issue.
| I work in a surgery suite; we have single-use (for sterility)
| items that use 8 AA's that will be discarded after five
| minutes' use. I effectively have all the free AA batteries I
| could ever use. Seriously, I could get easily get 40-50 a
| week if I needed them.
| tecleandor wrote:
| About the ML2032 option: that's the one that came with Dreamcast
| consoles. Lots of people swap it for an 2032 plus the diode when
| it fails, but I rather use another ML2032 or a different
| rechargeable thing to avoid opening the case again and again.
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