Remove the signal cables, a floating suggest no signal of small window, a window inside the characters and trichromatic color bars, etc. All showed normal. The machine without the circuit diagram, and according to the physical paint input part of the circuit diagram (sees attached figure, the figure on the label for the actual label on the original board). Measuring tube three cathode voltage are 40 v. Because the video preamplifier SID2552X03 - AO contains character generator of manifold blocks. To normal display character, which indicates that the machine's video preamplifier, video output amplification and tube parts are normal, fault should appear in the input part of the signal. 15 core type D measurement signal cables between input socket CN101 without a break. Respectively measured input socket CN101 (1), (3) feet of resistance direction are 3 Ω, 5 feet of direction are 20 Ω resistance. Release respectively DR02, DG02, DB02 measurement, found DR02, DG02 were breakdown, DB02 soft breakdown, check the other components are normal again. Replace the device, then test socket CN101 respectively (1), (3), (5) feet of resistance direction are 30 Ω. Because there is no computer host, the TV box was used as signal source alternative. Try boot plug in the TV box, image color all normal, watch for half an hour after consign is used, the end of maintenance work.Fbtservice manual download site