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Good afternoon: I have a sony STR K740P amplifier that keeps going nto Protecdt mode about every five minutes. I turn it off for a while then back on and it runs fine for another 5-10 minutes that back inprotect mode. What's up?

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Take it apart and clean it. The Sony home theater systems seem to be bad about protect mode.

Step 1. Disconnect power and attempt to turn it on with it unplugged, this should discharge anything that would kill you (Should)

Step 2. Remove screws from outer casing, insure that you don't drop any. If a screw drops and lodges itself under the board be careful retrieving it as some capacitors hold a hefty charge.

Step 3. use an air compressor and blow it out, make sure not to put too much pressure on it as some components may become de-soldered.

Step 3-A. If you don't have an air compressor and don't have money to go get one then use your lungs and a paint brush and just lightly brush all the dust off that you can. I personally used a makeup smudger thing and some alchohol to remove all the "Stuck" dust.

Step 4. WITH THE CASING STILL REMOVED, Allow it to sit for about 10 minutes and then try to plug it in with no speakers attached. You should hear a clicking noise from a relay.

Step 5. If you have not heard the click after about 5 seconds to a minute and it has gone back into protection mode then go back to step 3 and try a more thorough cleaning, alchohol and some Q-tips recommended just don't let any of the fuzz stay.

If you heard the click plug one speaker in at a time starting with the "Front" speaker, then check the settings on the console to ensure they match what the speaker is. You will need a multi-meter to check the resistance of the speaker if it reads around 8 then make sure the console is set to 8. Also ensure that you input the length of wire used into the console. All of the options are there.

Do step 5 until all speakers are connected and it is working, if it is still not working at this point go back to step 3 again and clean it again.

If it has overheated too far then it is possible that the "Drive" components have become faulty. If this is the case then guiding you further would probably be very stupid. You can however look at the "Chip numbers" or the numbers and letters on the components screwed to the heatsinks (The silver thing with fins) Get the numbers off of that and get someone to test and replace them as they are normally the problem.

To get power packed sound that rocks the roof and breaks the windows takes an enormous amount of current. The power dissipated from the components inside are radiating like a heater if it is full blast. Ensuring that the home theater system knows the resistance of the speaker and the length of wire helps to keep your system from burning like a resistive heater.

If you clean it tons of times with a deep clean and it still doesn't work look for someone who knows what they are doing and that you trust and take it too them. Most of the time when it comes to a thermal overload it just means that either the sensor is faulty or the component it originally sensed is no longer functional which keeps it in protection mode.

I am not very familiar with this home theater system and do not remember if it uses mosfets IGBTs or just high power transistors, but when I got mine it would not come out of protection mode until I checked it out. When everything read correctly I assumed it needed cleaning and most of the time it does.

This particular model seems to have overheating issues especially since there is no fan for the heatsink. If you would like more assistance shoot me an email at and maybe I can guide you through the process.

Posted on Oct 17, 2012

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U have an amp that is going into thermal protection mode. the reason maybe an overloaded amp. make sure the right ohms speakers are connected to ur amp. most amps will work with 4ohms with bridge mode, then there are amps that work with 4 or 8 ohms. if all conections are ok, the ouput circuitry is overheated. u need to get it checked by a qualified tech

Posted on Jun 06, 2010

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