I hate to be the one to say this but I think you are dreaming. Nortel wants you to buy replacement cards - they jealously guard their schematics and circuit diagrams. I think there are places that refurbish phones by cleaning them and making minor repairs but I don't know anyone who makes repairs at the board level. If cost is an issue try the 2nd hand and refurbish sites on the internet, that will ikely be cheaper than the effort it will take to troubleshoot and repair defective cards - especially 2 sided multi-layer surface-mount. I think your company is still thinking in terms of the 60s' - 80's electronics repair when it was cheap and easy to get parts and make repairs.
We have over a thousand cards installed on site and we have a failure rate of less than one a year. If you have several defective cards you may want to check the grounding on your switch.
