CoreBuilder 9400 Ports faulty

I bought a used CoreBuilder 9400 and it turns out that the first 6 Ports do not work properly. The Rest works fine.
If I connect another switch (I tested it with SS2 3900, SS2 3300, Extreme Network Switches) to one of the first six Ports, no connection can be established. When I look at the details for one of these ports, the autoNeg status is always "autoNegotiation: configuring" when another switch is connected. Of Course I tried to disable autoNeg on both switches and also tried several other port settings.
I also reset the nvData of the switch and I also installed several different firmware versions. But unfortunately, nothing helped.
The Switch schows no Errors and failures while booting.

I'm glad about any tip. 3Com was not helpful, they just said to send the switch in and that they will repair it at my expense. But we use it just for LAN-Parties from time to time, and it's not worth it to spend around 4000 USD just to get it repaired by 3Com. So, any tip is welcome

Please excuse my bad english, I hope I could make myself understandable.

Thanks and Best Regards,
Daniel