I think I can help you.
Try a slotket adapter with a Coppermine Celeron 566MHz (SL46T). From my experience it should at least POST, then the L2 Cache will probably not work due to the BIOS lacking the correct Coppermine microcode. This particular S370 Coppermine is pin-compatible with the Mendocino wiring. That's been my experience with a Zida CreateLX-CT, socket 370. It now works with all Coppermines with the right mod and the latest BIOS, but that breaks compatibility with most video cards. That's a tradeoff one has to be ready to make, at least with my model and the lack of a correctly modded bios at the moment.
In your case, since this is a slot 1 board, modding it to accept Coppermines is a bit more involved and I haven't done it myself, ever. But I was re-reading these instructions to mod slotket adaptors and I had some ideas for you to try.
The thing is that Mendocino Celerons (Socket 370) need pin AM2 to be grounded. While in the case of the Coppermines it should NOT be grounded or used at all. That's why the mod for a slotket involves isolating that pin.
Try to find what is the Socket 370 AM2 equivalent for Slot 1. I'm not sure if there is a pin for pin analog between Slot 1 and Socket 370. In case there is, you might have a chance.
Once you locate it, check without any CPUs or slotkets inserted, if there is continuity between the AM2 equivalent pin for Slot 1 and GND on the board. If that pin is grounded, then you should cut that trace and that will give you Coppermine compatibility. Your Mendicinos will probably still work, but I can't assure you that.
This will be of help http://ps-2.kev009.com/eprmhtml/eprma/f706.htm
hgoshev wrote on 2023-03-03, 07:52:it seems my PCB version doesn't support voltages under 2V
It shouldn't matter at least for testing purposes. Coppermines should boot fine with 2v but they will run hot.
You could just measure VCC and be sure!
Good luck!
