First rule out the possibility of a horn and wiring bad, ringing the 40 chord Y762, Y762 17, 18 feet is ringing output. See if the output is measured with the oscilloscope, must at the time of adjusting ring tone to measure, or in the 17th and 18th of Y762 welding a horn to determine whether there is output, no output is usually Y762 damage. When replacing Y762 didn't ring, the periphery of the main check Y762 circuit, mainly of 13 MHZ signal, (4) (1) the feet of the reset voltage (usually 3 v), 7 feet power supply 3 v, 20 ~ 31 feet of cable. If you have any waveform in U205 (2), attending the feet, but is not ringing U205 damage caused.RTbservice manual download site