The machine Hitachi 236 d type color TV, a grating, VHF channel without picture and sound, noise screen appears thick snow. YqCservice manual download site
 YqCservice manual download site
According to the user reflect first is fled after gradient is no image, thus doubt the local oscillator circuit fault caused by high frequency head, this machine VHF band the local oscillator circuit as shown in the appended drawings. L172 and L171 VHFI and VHF Ⅲ frequency oscillation coil respectively, D155 for frequency switching. Oscillation capacitance by D144 (varactor), C175, C176 and C179 composition. In principle, if the tails circuit oscillation stop, will lead to no images, no sound. Test the VT voltage is very low (normal in 0 to 30 v adjustable). Disconnect high-frequency head BT connection, outer end measuring 33 v voltage is normal, thus determine fault in high frequency circuit. To determine whether the local oscillator circuit to stop caused by vibration, can use two wire will oscillation coil respectively 1.172, short-circuit, L171 L172 and L171 screen after short circuit fault phenomenon, there is no change this resonance circuit has stopped. The local oscillator circuit is most likely to fail the foot varactor D171 and several oscillation capacitance. Finally found is D144 leakage, in a same model (ISS85Y) varactor, troubleshooting.YqCservice manual download site