[ Example 13 ] Symptom: noise appears when power on
Trouble description: press POWER button on remote control or control board to power on and off
on each input mode and you may hear “pop” noise during the courses.
Analysis and troubleshooting: according to servicing experience, firstly check mute circuit when
this kind of trouble appears. Shown in the figure 3.3.1.3, when power on, MUTE signal changes from low
level to high level, and output high level through D120. When power off, ce151 outputs high level
through D121 and the diode D21, R71 inputted to mute control circuit are added to base electrode of
triode Q119 to make triode Q119 saturated on, now MUTE end is low level to realize power-on quieting
effect. Now there exists noise when power on and off, so we judge that trouble lies in Q119 and its
peripheral elements. After test, triode Q119 has been stricken through. Change the triode with the
relevant model and trouble is removed.
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figure 3.3.1.3 mute circuit diagram
[ Example 14 ]
[ Example 15 ]
symptom: do not read USB
Trouble description: disc read is normal when in DVD state; after inserting USB, USB data cannot be
read out.
Analysis and troubleshooting: USB part is processed after being switched by electronic switch
ADG713 and then inputting to Mt1389. Firstly check whether channel is normal, from USB board to main
board through 22P flat cable cord and then to video main board, and this flat cable contact is bad. Firstly
check whether USBM, USBP are normally connected and whether there is short-circuit to ground. After
checking, USB board works normally. Then check lines on main board according to signal flow. USBP
passes through L158, so we judge that Mt1389 main chip cannot work normally. Check power supply of
each group and find that pin 49 USBVDD has no 3.3V voltage input. Check peripheral circuit and find
L191 has disconnected. Change L191 with the same specification and trouble is removed.
symptom: disc tray ejects out automatically
Trouble description: in DVD state, after loading disc, disc read is not available and disc tray ejects
out automatically.