HP-41 - port not working

[AndiGer]

Thank you for your suggestions.
It's a CV so no 82106A or 82170A memory possible.

Checked with X-Func in port 3 and X-Mem in port 4. EMDIR does report 124 with X-Mem in port 4, 362 in port 2.

Next I did a reset, Memory lost. After each try decribed below I did a reset to Memory lost so I have the basic configuration before next test.

Then plugged in X-Func in port 4 (calculator off). Then ON.
Sometimes the calc immediately freezes, does not respond to any key. With sometimes weird display 0.0000 00 00
Sometimes after a single key press it shows Memory lost and then is frozen.
If I then remove the X-Func module it works perfect. But switching to program mode it sometimes shows 00 REG 273 or 03 or 05 or even PRIVATE.

So I think the calculator recognizes the module plugged in (and is confused) but has some irregularities concerning the timing or phi line?
BTW: I have no oszi, only multimeter.

What I measured some time ago was the I/O block.
I have connections (0 ohms, as shown in the service manual)
from port 1 Vcc to port 3 Vcc and B4, B3 to B3.
Port 2 Vcc to port 4 Vcc, port 2 Vcc to B3, port 4 Vcc to B3 and B4.

Andi