Picture of the board please. Is it a Phoenix Bios v4 ? My old "Bigelows PC Tech" manual says same but Phoenix code 02 is also for Cmos R/W test.
Do you have a battery connected ? Please post a picture of your board, is possible other traces are bad....

Hello 😀

You're right it si not version 4. I've searched in bioses dump but i was unable to find which version is. According to necroware (https://www.youtube.com/watch?v=hc8Zut9DDXk) which repaired an identical mainboard, it should be v3.10.

Pictures of mainboard with details are in attachment. I couldn't get better ones. I'll try a different smartphone later.
All corroded bottom traces were checked and are fine.

Since it's a CMOS RW error I think It's something related to 82C206 chip, which holds RTClock and CMOS memory function. (NEAT chipset)

Battery circuit seems fine. With an external battery (around 5v) 82C206's PSRSTB (active low) receives around 4.2v. 82C206's PWRGD and VCC are both high (4.2V) aswell. When powered on Vcc(75), PWRGD, PSRSTB are all 5.05V (psu 5v rail is 5.05V). RESET instead is LOW (active high).

Both CPU and Keyboard IC are hot after some minutes (not burning, you can place a finger on them).

Should I replace 82C206? Should i desolder all logic 74XX chips and check them? Some of them could be failing due to age.

What do you think?