It is normal for the Z8 to get warm, that's not the problem 😀
When you say the diagnostics detect the MPU , do you get a screen similar to this? (perhaps a different eprom version in yours but the rest should be the same)

If you do get that then there must be a mistake in the cable or some component in the card failed and the signal does not reach the output DB9 connector. Can you post a picture of the cable you made? It's the solder connections that are important, maybe you soldered them in the wrong order - common mistake and happens to me all the time 🤣 🤣 🤣

edit:
btw, caches and processor speed are irrelevant to this mpu card - it's the game drivers that crap out due to speed. I have used the PCMIDI mpus successfully in pentium3 setups , so cpu/system speed is not an issue

Also, the card does not use a Z80 , it uses a Z8 mcu - so if you did order a Z80 don't plug it in...

I meant Z8. I got one with the same part number, Romless.

I did make my cable go straight from the DB9 to 2 male DIN 5 connectors, and tested continuity with my multimeter. It occurs that they may be inverted, since your original cable went to DIN5 females?

I'll take some pictures when I get home.

Yes, the schematic assumes you are making a breakout cable with female DIN 5 connectors, like the original cable. I am pretty sure that's the fault, inverted cabling. No worries as nothing gets damaged by that .

I just finished transposing the wires and it WORKS!
You might want to edit your original post to let people who are making straight db9 to Din5 Male cables to swap those around.

I'm so happy, this was the last internal component of my ultimate 486 build!