Only advise I can offer is to double check that the Necroware RTC replacement is working properly.
I recall recently watching a video on Adrian's Digital Basement where his Necroware replacement was faulty (probably bad solder or faulty chip).

Is there any floppy disk that came with the computer ?
If so, please make a copy of it 😁

Also I wanna see pictures of the box/manuals as this is a very rare occasion for me to get more infos about this machine.

In the meantime, yes I'd agree to check that the RTC works correctly first. I think it works fine on mine, but I should double check, I haven't tested it much since and I do remember having issues with the HDD (well I dunno if that's related to the bios as it's a very old and very quirky HDD). Some RTCs need a bridge between two pins to work properly (I think necroware made a revision of the PCB to do just this)

This module can be also used as a replacement for the Hitachi HD146818P RTC chip which was not only used in many PC mainboards, but also in other devices and home computers like the BBC Master. On some devices the pin 1 has to be pulled up to pin 24 (VCC, Motorola Mode) or down to pin 12 (Ground, Intel Mode) using a 10k resistor. This was tested by Adrian on his YT channel (he used a simple bodge wire, but it's safer to use a resistor: https://youtu.be/2Sgleturods?t=2970)

So
I have now tried two known working Dallas replacements, as well as battery modding the original Dallas that I desoldered.
I have also tried pulling pin 1 up to VCC and down to ground, also with zero success.
I wonder if this is the reason that the PC has never/barely been used!
No idea where to go from here sadly.
I shall photograph everything at some point for you Deksor
Andrew

Dodgy BIOS rom IC?

giantclam wrote on 2023-10-10, 07:08:

Dodgy BIOS rom IC?

I'm wondering about that. It reads ok in my TL866, but I know from experience, that's no guarantee. Unfortunately, I can't find any spare 512 kilobit EPROMs lying around, so I have ordered a bunch.
Cheers
Andrew