Cyberdyne, I did this a couple of years ago on my Soyo motherboard too, it works great, thanks. I also did the same thing to other motherboards that have the exact same recharging circuit (with different layout, obviously).

Now, I was putting together a diagram and noticed that after going thorough the resistor, the +5v line also goes to other components, aren't those components expecting the +5v line that has been cut off? I was able to trace that to a couple of tantalum caps and from there to a resistor array, I didn't trace any further and came here to ask since I'm no expert. Any Idea what's going on there? Is this mod disabling something else that I haven't noticed yet?

What's also confusing is that the positive of the 3v battery is also going in that direction.

Dusko wrote on 2021-02-06, 09:31:

Now, I was putting together a diagram and noticed that after going thorough the resistor, the +5v line also goes to other components, aren't those components expecting the +5v line that has been cut off? I was able to trace that to a couple of tantalum caps and from there to a resistor array, I didn't trace any further and came here to ask since I'm no expert. Any Idea what's going on there? Is this mod disabling something else that I haven't noticed yet?

Your diagram looks about right. The "other components" are supposed to be the real time clock only (and maybe a tantalum cap for decoupling). They are powered through the upper right diode from the battery when power is off, and through the lower right diode when power is on. The diode and resistor on the left are the NiCd charging circuit. This circuit should be disabled when converting the board to lithium primary cells (by cutting a trace or removing one of these components).

I had a similar problem as reported in this thread: The converted board drained lithium cells in weeks. The reason was that the diode in the lower right position in your diagram was shorted, allowing the battery to power the 5V lane when the supply is turned off. Replacing that diode by a working one fixed the issue.

Thank You mkarcher, I have it more clear now. So it looks like it's the perfect solution for many 486 motherboards since I was able to find the same flow on several of them in my collection, except for the ones that have an RTC Odin or Dallas clock, I modded those with an external cell battery.

I modified the Hell out of my SY-4SAW2 Motherboard. Enjoy:
https://www.youtube.com/watch?v=eUaoXPgnZvo

galanopu wrote on 2022-04-21, 03:09:

I modified the Hell out of my SY-4SAW2 Motherboard. Enjoy: https://www.youtube.com/watch?v=eUaoXPgnZvo […]
Show full quote

I modified the Hell out of my SY-4SAW2 Motherboard. Enjoy:
https://www.youtube.com/watch?v=eUaoXPgnZvo

nice mod, i bought 4saw2 about 3 times in the past 5 years. All had massive battery damage, green stuff even below the ISA slots and memory sockets. And all components left to the diode were eaten, and traces were eaten, and Bias were destroyed. Too much of a job to repair.

It was last year where a seller who lives in an area where it never rains and is very dry all year, that offered me one of those for a good price, and it was the first time i had in my hands the 4saw2 motherboard without battery damage and working. Of couse the first thing i did was to remove the battery and i really like the board.

Can you share the list of capacitor values and voltages that you bought and the specific link to mouser or digikey that you use? i also do not like tantalum caps because of fireworks

BLockOUT wrote on 2022-04-22, 03:33:

nice mod, i bought 4saw2 about 3 times in the past 5 years. All had massive battery damage, green stuff even below the ISA slo […]
Show full quote

galanopu wrote on 2022-04-21, 03:09:

I modified the Hell out of my SY-4SAW2 Motherboard. Enjoy: https://www.youtube.com/watch?v=eUaoXPgnZvo […]
Show full quote

I modified the Hell out of my SY-4SAW2 Motherboard. Enjoy:
https://www.youtube.com/watch?v=eUaoXPgnZvo

nice mod, i bought 4saw2 about 3 times in the past 5 years. All had massive battery damage, green stuff even below the ISA slots and memory sockets. And all components left to the diode were eaten, and traces were eaten, and Bias were destroyed. Too much of a job to repair.

It was last year where a seller who lives in an area where it never rains and is very dry all year, that offered me one of those for a good price, and it was the first time i had in my hands the 4saw2 motherboard without battery damage and working. Of couse the first thing i did was to remove the battery and i really like the board.

Can you share the list of capacitor values and voltages that you bought and the specific link to mouser or digikey that you use? i also do not like tantalum caps because of fireworks

Thank you 😀

The specific ones I used are not available there, so I can not give links.
All caps have 5mm diameter and are of the solid polymer type.
In the end I overdid this end used 330u/16V for the 12v and -12v and 680u/6.3v for the low voltage rails.
The original caps were way smaller in capacity, and in the end it does not make a difference.
So just go and buy any reasonable priced 5mm polymer ones and you are set.