Audio Systems: Protection mode activates at too low levels., output transistor, amplifier section

Question
JVC Model CA-D661T Compact Shelf System (3-CD / 2-Tape / Tuner / Aux input)

MY PROBLEM:
About 4 years ago the amp started cutting off sound at the higher volume levels (above 15), with a little “click” sound coming from behind the front panel. We have been able to live with it until recently, but now it cuts off sound around level 12, which is audible, but only if you are standing next to the unit.  This problem applies to all modes of operation (CD, tuner, cassette, and external input), and it gets worse with the "Bass On" button selected. There are no additional speakers connected to the unit, other than the ones that came with it. From what I’ve read, it is clear that the unit is going on “protection mode”.  I have checked all external connections, and even carefully opened the panel of both speakers and the unit itself and found nothing obvious.  

JVC wants an arm and a leg to fix it, and other authorized service centers (none of them close) want me to bring it in before they can quote me.

Is there something I can do here, short of buying a new set?


Answer
This protection activation is most always associated with overheating of the output transistor block in the power amplifier section.  And, in your case the condition you describe, that of the protection tripping as power level is increased, is classic.

The cure is usually replacing the heat transfer grease (it gets old and dry) between the power transistor block/module and the heat sink that draws the heat away from the transistors.  However, it is quite expensive due to the great amount of labor in tearing the power block down and regreasing and replacing everything.

If the set is getting along in years - say over 5 years, it could be time to just replace the whole thing with a new generation set.

You can try putting an electrically insulated cold pack over the heat producing power section and see if that keeps it from going into protection.  This would be only as an experiment to prove it out.  Then you will know that is the problem!

Another test is to disconnect the speakers from the central unit and run it at max setting of the volume.  If it does not go into protection then you know it is the power thing as above.

Does this help?  Let me know if you need more.