A normal CR2032 battery is enough in most cases...

You could just remove the old RTC, add a socket, and buy a new one.

RTC...
https://www.mouser.com/ProductDetail/700-DS12887
https://www.mouser.com/datasheet/2/256/DS1288 … 87A-1512672.pdf

Socket...
https://www.mouser.com/ProductDetail/517-4824-6000-CP

I am wondering if I can solder the coin battery housing wires to the motherboard location for a barrel battery and then maybe jumper a wire for ( jumper J10 ).

That's not the symbol for a barrel battery. That's an unpopulated resistor.

dr.ido wrote:

That's not the symbol for a barrel battery. That's an unpopulated resistor.

Okay, thanks.
Looks like I will just have to dremel into the battery.

This is a recurring question and I don't know how people always fail to find the solution by vogon's user maeslin. He designed a small PCB that replaces that dallas horror show. No more butchering needed! I made a few of those myself and they work like a charm.

Half-Saint wrote:

This is a recurring question and I don't know how people always fail to find the solution by vogon's user maeslin. He designed a small PCB that replaces that dallas horror show. No more butchering needed! I made a few of those myself and they work like a charm.

Where is it ?
Looks like i’m Going to have to drill into the side of the Dallas next to the BIOS chip.
What a pain.
Anyone do this before ?
See RED marks.

You can get one of these https://monotech.fwscart.com/DS12887_RTC_Drop … 4_19810725.aspx

Well, I would if I could. But the dallas is soldered to the motherboard. So the easiest solution is to just
Drill into the dallas and solder on a coin battery holder.

It'd be easier removing the whole thing, fit a socket as suggested, then either a new RC or the one I linked too.

You can also use a supercapacitor connected to the nearest +5V supply through a Schottky diode. It will hold enough charge for a day or two which is enough in most use cases.

What I did for my 486 board was almost the same as suggested, you can cut into the Dallas battery (very carefully) until you reach both the positive and negative lines. I didn't use a CR2032, what I did was buy 3x 1.2V *Rechargeable Ni-cad batteries & stuck them in a small pack, then soldered the leads to the + and - lines you cut into. It's a bit tricky, but once done, you'll never need to worry about the battery again.

dave343 wrote:

what I did was buy 3x 1.2V *Rechargeable Ni-cad batteries & stuck them in a small pack, then soldered the leads to the + and - lines you cut into. It's a bit tricky, but once done, you'll never need to worry about the battery again.

How do you expect them to recharge? They'll be dead within a month or so.

jmarsh wrote:

dave343 wrote:

what I did was buy 3x 1.2V *Rechargeable Ni-cad batteries & stuck them in a small pack, then soldered the leads to the + and - lines you cut into. It's a bit tricky, but once done, you'll never need to worry about the battery again.

How do you expect them to recharge? They'll be dead within a month or so.

Maybe he recharges them manually. All NiCd batteries experience the so called memory effect. If they are routinely recharged before depletion, they lose capacity quickly. Maybe 100 cycles or so.

This is what I ended up doing for another one of my 486 boards, but it had the corroded barrel battery. You can do this same setup for the Dallas battery, you just need to cut into the battery and solder onto the + & - leads inside.

I've noticed all my 486 boards have exactly the same topology, so I've traced the circuit, drawn a schematic, and modified them to put the battery itself behind a diode, while still allowing the board to run the RTC from the +5V rail when powered on. Then, there's usually a 20mm-spaced pad on that battery area on the motherboard where you can mount a primary coin cell holder for easy maintenance every 15-20 years or so.

I don't think that helps with the 12C887-style circuits, since those assume a primary cell as part of the module. For those (a PS/2 and a couple 386 boards), I made a replacement PCB with the 885 variant RTC (no integrated battery or crystal) and a coin cell holder. The picture above looks more like the 486 boards I've ended up with, though. Those have a discrete crystal oscillator circuit built around a hex inverter, then the battery and 32kHz clock run over to the chipset. There's no dedicated RTC.

dave343 wrote:

This is what I ended up doing for another one of my 486 boards, but it had the corroded barrel battery. You can do this same setup for the Dallas battery, you just need to cut into the battery and solder onto the + & - leads inside.

No you can't. Barrel batteries get recharged when the PC is on, Dallas batteries do not so replacing them with rechargeables is a waste of time.

I found these how-to's.

Just need to drill under pins 16 and 20.

Video
https://youtu.be/NdlSfqto_0o?t=47

Manual
https://datasheet.octopart.com/DS1287-Dallas- … eet-7278225.pdf