TCL DVD-F70, Руководство по обслуживанию

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5
b). Check w5V voltage is normal.
c). Check whether laser voltage ( about 2V for VCD and 2.2V for DVD respectively ) exists at the C
pole of Q1 and Q2, and whether U2 and adjacent parts are damaged or weld falsely.
d). If the above parts are normal and no laser emits, replace the loader.
b. Read no disc
a). Check whether the ribbon wire from 24P to loader is in good contact.
b). Check whether the RFO signal of the 10th pin of CN6 is transmitted to the 96th pin of U1.
c). Check whether laser voltage (about 2V for VCD and 2.2V for DVD respectively) exists at the C
pole of Q1 and Q2, and whether the voltage is normal.
d) Check whether U1, U2 and adjacent parts are damaged or weld falsely.
e). If the above parts are normal, replace U1 or the loader.
c. Read DVD discs only or read other discs beyond DVD only
a). Check whether the ribbon wire from 24P to loader is in good contact.
b). Check whether laser voltage of 2V outputs at the C pole of Q2, and whether the 125th pin of U1
is at low level.
c). Check whether the pins from the 1st to the 38th of U1 and adjacent parts are weld falsely,
damaged or erode.
d). If the above parts are normal, replace U1 or the loader.
3. Troubleshooting and service of decoding part
a. No video, no audio, no display on VFD, and no operation of keys
a). Check whether the power sources of the decoder board are normal.
b). Check whether there is 27MHz signal output. If not, X1 crystal and adjacent parts are eroded or
damaged.
c). Check whether there is 81MHz signal output at R64. If not, check whether there is short circuit,
false welding or alien substance for audio D/A circuit U5 and SDRAM U8 and U9.
d). Check whether the reset circuit composed of C7, R37 and D1 is normal (constant 0V after tens
of milliseconds of high level). If it is at low level constantly, C7, R37 and D1 are damaged.
e). If the reset level is normal, check whether the chip selection signal, address and data of the 12th
pin of U5 are normal.
f). Check U10 that whether the data of pins from the 1st to the 8th, hsync and vsync signal of the
10th and 11th pins, and 27MHz signal of the 29th pin are normal, and whether C162 and R68 are
normal. If not, replace U10.
g). When U5 works normally, check the connection between U8, U9 and U3. If abnormal, replace U8
or U9.
h). Replace the main chip U3 after making sure no damage to the adjacent parts and no short circuit
or false welding for the circuit board.