"alex goldman" skrev i en meddelelse
...
wrote:

Physically broken/cracked surface mount components or the solder
connections to same. Rarely visible to the naked eye.

Is it practical to try to diagnose it further, and if so, how?

Microscope - and maybe x-ray the board. I would only do it if it was my
prototype coming back from testing ...

Is it possible to fix a motherboard if it has such problems somewhere
(broken/cracked surface mount components or the solder connections to
same)?

Hardly Ever - Only *If* it is someting trivial like a component visibly
cracked or fallen off or *maybe* a pin on an IC not soldered in properly.
Often it will be a broken via inside the PCB or a joint underneath a 480 pin
BGA, in which case you need the x-ray machine.

If so, what kind of equipment, knowledge and time commitment will I
need?

Ebay for "SMD" rework equipment. In general it will be cheaper to buy new
than the salary you would have to pay yourself.