TV/VCR/Stereo Troubleshooting/technics sa-gx470

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Question
hi. i have a technics sa-gx470. when i bought it, it worked fine for a few days and then it started going into overload (as it said it on the display and didnt play any music through any input) all speakers where within the recommended impedance and the speaker cables where not shorted. my uncle (without my permission) opend the receiver up and took one of the ribbon cables out (that lead to the fan) there was a greenish spark and then he put screwed the case on again (i was obviously really frustrated by his actions) now. when i plug it in. the red standby light still comes on but when i press the on button nothing changes on the display after that.
can you please tell me if there is anything that needs replacing (and if so, what is it called and what are the details of it) and what else needs repairing/replacing or uprating

i would be extremely greatfull if you could reply helping me what to do to fix my receiver.
thanks alot in advance.
regards zuhayr rehan

Answer
It is very difficult to guess what may have failed.  You did the right thing by checking the speaker impedance and wiring as that is the most common source of causing overload symptoms.

You did not mention if you checked each speaker.  A shorted voice coil in a loudspeaker, for example, can cause the overload to activate.

Overloading can also be a circuit failure inside the amplifier.  If a channel is over driven for a long period of time caused by the volume level set too high it can cause amplifier burnout or failure of the output transistor which - as above, can cause overload protection activations.

Now it seems a more permanent failure has occurred and perhaps the power supply has failed in some way.  A shorted amplifier stage can cause internal fuses to blow or rectifier bridge to burn out or in the worst case a burnout of the power transformer - heaven forbid - which is a very expensive repair.

I suggest you disconnect all speakers, unplug the power cord from the mains for at least 30 minutes and try it again.  If still does not come on you have internal problems that will require troubleshooting.  If the unit comes then try connecting just one speaker at at time in which case you might find a bad speaker.

Maybe these ideas will help you get a solution.  Hope it helps.  

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Consumer Electronics of all kinds. Audio, esoteric audio systems and components, video, tv. Digital equipment for consumer use. Ham radio and automotive electronics. Note: I give advice on tv repair based on general consumer electronics engineering experience but I am not engaged in actual repair of sets. MAKE SURE YOU GIVE THE MAKE AND MODEL NUMBER AND AGE OF THE SET. BE SURE TO CHECK YOUR EMAIL FOR THE RETURN ANSWER DURING THE NEXT 24 HOURS AS I TRY TO REPLY TO ALL QUESTIONS WITHIN THE SAME DAY IF NOT THE SAME HOUR.

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