If the three signals are absent, there would have to be a common point between them, so there is the local power supply.

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Signal A, B and R on DIGITAL IF come from of the 3 outputs of samplers at 4kHz via motherboard.

Check TP12, TP10 and TP11 connected to input lines from mother board.

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If there are no signal at theses points, problem is near samplers?

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