Can this be repaired?

[Q] I would like to know if Motorola DR 3000 network card (PLMN5644B) can be repaired. We are experiencing serious problems with these cards in many repeaters. To get the cards from distributer has become problems as the product is no longer supported by Motorola. [sic]

[A]. It depends on what you mean by repaired?

If you want to repair this board yourself, you would need the the equipment to do fault finding; the tools to carry out surface mount rework and the knowledge to carry out the work etc.

The main challenges will be that there was no detailed service manual for this repeater (see this post). If you were able to visually identify the faulty component (e.g. transistor with the magic smoke hole in it), it will probably not be orderable from Motorola Solutions, even if you know what the part number is. PMLN5644B mostly contains discrete components which you could, in principle, source yourself. There are however a few ICs, and at least one them were discontinued some time ago by the manufacturers with no substitute.

PMLN5644B does not actually carry out any ethernet functionality. This is (was) actually done on the indicator board PMLN5643A. So only replacing PMLN5644B may not restore normal operation. In terms of literature and replacement parts, here too, you would experience the same challenges I described above.

If you want to send the board somewhere for repair, none of the Motorola Solutions repair depots will not accept obsolete equipment or boards for repair. There might be an independent workshop that would be willing to take on work like this - if there is, I imagine that they would leave their details in the comments.

However, from what I've seen, the main cause for dead ethernet on the DR3000, was lightning damage. The root cause was typically grounding issues (see this post) and/or the use of unshielded ethernet cable.

I used the word was above, because the DR3000 was discontinued in 2014. As far as I can tell, PMLN5644B went obsolete in April 2020, though there might have been residual stock in the supply chain after that. The DR3000 was replaced by the SLR5500 which, in my opinion, is a far superior model in all aspects.