The pairs in a CAT5 cable are used as follows
Blue (4&5) Left Audio
Orange (1&2) Composite Video/S-Video Luma
Green (3&6) Right Audio
Brown (7&8) S-Video Chroma
The IR channel is carried as a phantom signal over the left and right audio pairs
The SCART Control signals are carried as a phantom signal over the video pairs.
As long as you have three working pairs and connect them to 1&2, 3&6, 4&5 you will be able to get your KAT5 units working with Stereo Audio, Composite Video and IR Passback.
You will almost certainly lose the SCART control feature although there is a faint possibility that it will still work if one wire of the damaged pair is intact. You may get a slight bit of picture disturbance momentarily when the SCART status changes but if you dont have SCART switching signals fed to the transmitter then no data would be sent so that wouldnt be a problem.
Hopefully that solves your problem and that I have explained it clearly enough. Any problems drop me an email and I will be happy to discuss it over the phone if that would be easier.
keith at diyha dot co dot uk