Building a replacement 386/486 CMOS battery | Hacker News Reader

Building a replacement 386/486 CMOS battery

rubenerd.com

62 pointsBrajeshwar35 comments

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

Necroware has a replacement design for Dallas RTCs: https://github.com/necroware/nwX287

I don't know why there is a replacement design. You can still buy them new from Mouser. They last 20 odd years usually.

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.

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.

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.

>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...

You can also heat them up, making the resin brittle so you can chip it away and replace the battery.

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.

There were lots of test equipment with variants of those, and unlike CMOS settings, they held critical calibration constants.

Dedication and a cutter knife do it. I did it myself, twice.

Once while it was soldered into a mainboard :P

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."

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...

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.

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.

Got it thanks. That link crashed Mouser the first time so I assumed it was a dead one :)

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.

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

Why not use a 5F/5V supercapacitor, DGH505Q5R5 or anything alike ? You may need to solder a 10R current reducing resistor in series.

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.

You don't need that much of energy to keep CMOS memory and RTC clock running. The battery will self-discharge way before it's exhausted by the load. IMHO.

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.

What advantage does a supercap have over batteries?

Supercaps don't not leak and do not require to be changed regularily. Yes, offline time on supercap would be small, a couple of months, but for a machine which is used often that is not a problem.

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

AA or AAA batteries will leak.

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.

Lithium AA or AAA batteries won't, nor will good rechargeable.

I just took some lithium AA batteries out of a system that were 25 years old. Not even a hint of leaking.

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/

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.

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.

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.

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.

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.

The NiMH Duracells are very high quality (at least according to Project Farm).

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