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LG GSA-4040B Service Manual page 87

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2. LED does not blink at all at the time of a power supply injection. Eject-SW does not react.
(1) Is it normal to the exterior Bus (Data-Bus, Address-Bus, control signal system) of MPU?
Viewing — check: -- a short circuit, opening, etc.
• The device connected to the exterior Bus of MPU, and its signal list
Peripheral device
[Bus/Signal]
Address
Data
CS*
WCK
RCK
=> It repairs, when abnormalities are discovered.
(2) Does the power supply circuit operate normally?
When the abnormalities in external input 12V, 5V, regulator 5V, regulator 3.3V, and regulator 1.5V => are
discovered, an external power supply, a power supply cable, and Regulator IC are exchanged. Since a
problem is in a load side when not improving, even if it carries out the => above mentioned exchange, a JR2
power-supply system figure is made reference, and poor portions, such as a short circuit of a power supply
part, are found out and repaired.
(3) Is the clock of MPU oscillated correctly?
Checked the ceramic oscillation element's X801 both-ends and MPU (63), (64) 5MHz oscillating. When 3.3V
power supply is correctly supplied to =>MPU and the clock is not oscillating correctly, it is the defect of MPU,
or an oscillation element defect, and part exchange is performed in order of MPU and X801.
(4) The defect of Flash-ROM
Although the clock of MPU is oscillating correctly and the power supply circuit is also outputting normal
voltage, when LED does not blink at all at the time of a power supply injection and Eject-SW does not react,
either, poor Flash-ROM is the most doubtful.
=> Flash-ROM (IC802) are exchanged.
Note: Before Flash-ROM exchange, all CS signals of the external device of MPU connection, an Address
signal, and a Data signal are observed on a waveform level, and since the but most amount of work and the
special knowledge which can raise the discovery accuracy of a poor part are necessities, recommendation
is impossible.
(5) Even if it performs the above-mentioned repair, when not improving, the disconnection and the short circuit,
which cannot be discovered, can be considered in viewing of PCB. Moreover, partial breakage (although a
clock is oscillated, somewhere in insides do not operate.) of MPU can be considered. In this case, the
external device connected after [of MPU / MPU] exchange is exchanged in order. When not improving by =>
above, the possibility that a PCB pattern is faulty is high, and judges repair to be difficult.
Flash -ROM
(IC802)
A1~A20
D0~D15
XCS0&XCS1
XWRL
XRD
S-RAM
(IC803)
A0~A15
D0~D7
XCS2
XCS6 & XCS7
XWRL
XRD
DSP
(IC701)
A0~A10
D0~D7
XWRL
XRD
89

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