Hi Jose,
Use the SECOND set of schematics in the FT-980 Technical Supplement, which can be found in the "Files" section, not the debugging/alignment schematics which are earlier in the Supplement.
For the IF unit these are located on pages 182 and 183. I usually print both pages out on 11x17, and then align and tape them together.
--
-Mat Breton, N8TW
Mat Breton N8TW