Have you tried AT keyboards on the 486's (without adaptor)? For the most part I use the same type of adaptor on a variety of keyboards/motherboards and haven't run into issues so far.

Edit: I was thinking. Could it be that your keyboard is too new for the 486 boards? What kind of keyboard is it?

PS/2 to AT adapters are passive; at the electrical/software level an AT and PS/2 keyboard is the same.

As the above poster mentioned do they work with an AT keyboard?

Some old boards have a fuse near the keyboard that will blow if someone spills a drink on the keyboard (or connects a keyboard that has been damaged that way and has a short). So you could check it with a multimeter. And of course, the keyboard port tends to be right next to the barrel battery.

Sure, they both work fine with a true AT keyboard.
I'm using an old PS/2 generic keyboard, and tried another HP PS/2 keyboard I had lying around, no difference.

The PS/2 keyboards behind the adapters receive some power as the num lock etc.. light on and off on key press. But the BIOS gets stuck at "keyboard error" and pressing F1 to continue doesn't do anything, nor Del to go into bios.

Motherboards are PCPartner OPTI 486 VI & QDI V4P895P3/SMT...both react the same. No barrel battery, no damage.

I'm using adapters like this off eBay: https://www.ebay.com/itm/265155844755

I have several of them. Same adapters and keyboards work fine on a later Zida Tomato BX98 board. That's why I wondered if there was something different with these old 486 boards... this is weird 🙁

The HP keyboard I'm talking about is one of those infamous standard keyboards that were probably in half of all companies in early 2000 😀 I'd expect them to be super standard and compatible?

Boohyaka wrote on 2022-06-27, 06:24:

I'm using adapters like this off eBay: https://www.ebay.com/itm/265155844755

I have constant issues with these. Repositioning the cable sometimes helps, which tells me it's a pin contact issue within the adapter. Once, shoving some tiny bits of tinfoil in the holes seemed to make it more reliable.

interesting, thanks Roger Pierre 😀 I will make some tests to try and see if that's indeed a contact issue? That would mean I've been pretty (un)lucky on the perceived consistency of the issue, which I definitely don't rule out.

Any suggestion for better quality adapters?

Also at some point I may just as well solder one of the adapters to a PS2 keyboard if that's the case 😀

I don't know if it's better quality, but there is the dangly type that I haven't tried yet:

https://www.amazon.com/SF-Cable-Female-Din5-K … d/dp/B0016RTMQE

Not that I think being dangly will be some sort of magic fix. But I might try one of them anyway. I use the reverse kind without any problems:

https://www.ebay.com/itm/265155844755

[edit]

I've just bought one of these. I'll report back when it arrives one day. https://www.ebay.com.au/itm/352419542783