LG RX8 S-PROTECTION PROBLEM

[vincent mutale]

I have a problem with an LG RX8 HiFi system I bought 6 months ago from a reputable dealer Game Stores. When it plays for approximately 2 minutes its shutting off and brings above message. I tried some trouble shooting to see what could be the problem. All the output speaker ports are functioning. But one speaker seems not to be okay the Rear. But even disconnecting this speaker the System is still shutting down.

 

[kellys_eye]

The amplifier associated with that speaker obviously has issues. Since it appears to work for a short while I suggest this is a heat-related problem and may be due to either a large capacitor being faulty or the output device (IC or transistor) not being properly heatsinked i.e. the insulating paste potentially having dried out and allowing the component to overheat.

I'd put greater odds on it being a capacitor fault though.....

 

[73's de Edd]

Sir vincent mutale . . . . .

Here is the extreme left copy of one power output stage, all of the other ones are over to the right, being duplicated, just as this one is
There is the Class D processor and driver as the YELLOW rectangle IC.
There are two FET POWER AMPS as the YELLOW CIRCLES
There is the common YELLOW buss at the top that samples the voltage from each of the other amp stages and dump into that common buss
by using multiples of the PINK Rectangles 100K sampling resistor.
If there is DC voltage . . . as low as 2VDC . . . on your BLUE buss that feeds up to the speaker at the very top, it triggers the detector circuitry in the cluster of 5 transistors at far top left.
There is a another YELLOW sampling buss at the bottom which is doing the same with a 68K resistor that is samplinhg across a 100 ohm resistor in each amp stage. A fault in that circuitry trips the Amp Protect Circuitry and Amp Power Down.
On testing the top YELLOW buss:
You will have a DC metering on a YELLOW buss and its other lead to ground and you just have an instant after turn on to see if a DC voltage is present.
If finding such, initially lift an amps equivalent R7F34 . . .100K resistor and then retest and see if there is DC voltage on its BLUE buss

The voltage testing presence is also true on testing the lower YELLOW buss.

LG Power Amp Stage COPY . . . . .




73's de Edd

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