A "squeak" sound, switch power supply has been working. But to "cob" sound, switch power supply is not working in the line frequency. The fault is still in the line scan circuit. 84tservice manual download site
(1) measure the switch tube boot Q901 collector voltage of 285 v, normal. Emitter voltage is 110 v, the normal is 116 v, slightly lower. Measured again observation kinescope filament, not bright, line voltage output pipe work, collector 110 v, the base and emitter is zero, that line output stage did not work. 84tservice manual download site
(2) using a multimeter dB file T721 line drive transformer primary voltage, secondary voltage, output pipe line Q781 base has ac voltage. That line driver stage before work all normal, fault line output stage. 84tservice manual download site
(3) remove Q781 positive and reverse resistance measurement, eb junction have been found. Due to the overlap control pulse then through Q1110 inverting amplifier, via CP004, C401. Transformation's 1 ~ 5. 2 v is the voltage control, send to IC201 13 feet. IC201 audio volume control with dc amplifier, a control IC201 11 feet output volume, pressure increased control over 13 feet turtle, improve audio amplifier output audio signal amplitude, 11 feet 84tservice manual download site
Increased. 84tservice manual download site
(1) the first check the audio power amplifier, because of the audio power amplifier consumed power is big, easy to damage. With screw in rC20l @ feet into the human body induction signal, the speaker issued "raise price" sound, audio power amplifier working properly. 84tservice manual download site
(2) to measure IC201 13 feet voltage of 0.8 V, by VOL, the UP button, display from 0 ~ 63 continuous change, but 13 feet voltage constant. 84tservice manual download site
Measured again IC1101 41 feet voltage, the voltage varies with the volume display series change. Indicates the microprocessor IC1101 work, failure in IC110141 feet to IC201 13 feet with circuits. 84tservice manual download site
(3) check Q1101, C404 all normal, fault in thick film piece CP004. After replacing CP004 sound back to normal.84tservice manual download site