So, I passed the last 24 hours going crazy around this. I tried following every step, but for starters, nowhere I found any freezing references, and all signals test good on my DSO. As soon as I mount the f**** GPIB card, the counter freezes, after three seconds. I can do anything in those three seconds, and the device will respond. Then it just locks up. Does not matter, either card I have gives the same result, and instead both test good on the 6669 I'm selling. No error codes on the display at startup (and in extended mode the screen is blank anyway).
However, in extended test mode, and with the card mounted, it does not freeze - it does the relay thing, and if I move the jumper as described, it stops doing that, but does not freeze. However, in this case something does not add up, I cant manage to get the signals described on the manual, on the referenced pins. Not sure I am doing anything correctly, the text here does reference other chapters of the manual, i.e. the I2C description chapter.
I also learned something new, the I2C bus includes the TXCO and prescaler, I did not see this on the circuit diagram I had. Possibly it uses the protocol on the"ident" lines I found? No SCL/SDA go to these options, unless I'm blind.
I admit to be a complete noob and hobbyist.
Ahhhh.... I'll just wait for the whole manual, and see if it could be a power issue in the meanwhile. Tomorrow I'll check up currents too from the MB to the GPIB card.