Remove the SN board from your set , I hope you have a meter? with meter set to low ohms (200)test across the two pins of the SN2 socket on the board , a low ohm reading is a fail. if you meter reads OL or whatever it reads when the leads are apart move on to next test, find test point VFG just above the last but one buffer(on right) ICs (with ribbon connectors towards you) with meter set as before (low ohms) put one lead on the test point VFG the other run across all the ribbon connectors gold contacts any low ohm reading the buffers ICs have failed, buffers that show no low ohms are fine Please try these tests and give me the results Regards John