Engineer joke - Continuance

Wednesday - Last week:
Today I dived deeper into the oscilloscope and it's service manual.
Now I know what the messages are mean:

CAN'T COMMUNICATE WITH UFO - I can't communicate with the front panel (handles)
WRONG AI HARDWARE VERSION - That AI is not AI but A1. I can't communicate with the analog board
NO ACKNOWLEDGE ON IIC - This evidently comes from the first two.

The construction of the unit is something like this:
There is a main board what is a passive backplane. The power supply and the processor board is plugged into this. A cable from the processor board goes to the analog unit and from the main board one to the front panel and one to the display electronics. From this the communication between the display and processor board is working.
The processor is not able to communicate with anything else. This points me to some I2C bus error. I  tried out what happens if I disconnect the two cable of the error designated units one-by-one. This action doesn't eliminated the other board's error in any case. I presume based on this that I've a general problem with the I2C bus. Maybe the pullup is missing (the I2C is some kind of Open Collector bus, so not works without pullup resistors) or the clock generation has problems.
I think, I'll not solve this. So goes to a repair guy or back to the seller.
Friday:
I visited Mr. Urban (he is a famous shop owner/designer/repair guy here in Budapest). After looking to the unit, he said, he not take it, because it is a newer construction that he have knowledge on.Monday:
I still wanted a working unit. Asked the seller if I can send it back for repair and I pay both of the shipping charges.
He said that his technician is only able to use it but not able to repair it. So I've two options. I send it back and I get back my money(without the shipping costs), or I keep the unit and he sends back the half of the money. I chosen the later option.
Now I've two original probes (I had before only two Chinese crap and a half broken, repaired Philips), and a bad scope.
I take a deep breath and try to repair it. Most probably this effort will fail, but I'll learn a lot from it.Yesterday:
I've a little more chance. I found a processor board on the ebay, what together with the shipping charges cost less than the amount will be refunded from the scope. Now I just need to proof if this card is bad.
to be continued ... (when I start to repair it)