LG Electronics GSA-4168B Does the power supply circuit operate normally?, The defect of Flash-ROM

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 in DSP, and its signal list

Peripheral device	Flash -ROM
[Bus/Signal]	(IC302)
Address	A1~A20
Data	D0~D15
CS*	CS0B
WCK	WR
RCK	RD

=> It repairs, when abnormalities are discovered.

(2) Does the power supply circuit operate normally?

External input 12V, external input 5V, regulator 3.3V, regulator 2.8V, and regulator 1.5V

=>When the abnormalities 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 exchanges the above, and attached sheet JR6 power-supply system figure is made reference, and poor portions, such as a short circuit of a power supply part, are found out and fixed.

(3) Is the clock of MPU in DSP oscillated correctly?

Checked the ceramic oscillation element’s X301 both-ends and DSP(106)(107) 33.87MHz oscillating.

=> When 3.3V power supply is correctly supplied to DSP 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 DSP and X301.

(4) The defect of Flash-ROM

Although the clock of DSP 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 (IC302) are exchanged.

Note: Before Flash-ROM exchange, the CS signals of the external device of MPU in DSP 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 DSP can be considered.

=> When not improving above, the possibility that a PCB pattern is faulty is high, and judges repair to be difficult.

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