Diagnosing bad amp - New member

[The_big_dill]

Hey all,

I have been collecting speaker components and have finally got enough to upgrade my speaker system for free.

After all was installed, I find the amplifier is no good... goes to show that free is never easy

The amp is a Kenwood KAC-5201, not powerful, but enough to power front speakers.

The problem:

When powering the amp, the power light flickers fast, probably at 5-10hz, and some static is heard in the speaker at the same rate as the light is flickering (albeit, the speaker isn't visibly moving). If powered for long enough, the fuse blows.

The bottom left of the amplifier was getting super hot within seconds of operation (view wrt label of amp), right at the output transistors.

What I tried:

I did some research and confirmed that there was good power and ground to the amplifier and checked using a known working speaker I had on the side (to eliminate the possibility of bad wiring or speakers).

I opened the amplifier cover to check for any burnt components and checked the PCB on both sides, and everything is clean.

I powered the amplifier with the cover off for about 5 seconds and determined that it was 2 of the output transistors that were extremely hot to the touch (I would estimate ~80-90 Celcius)

Checking the transistors for internal shorts, led me to believe that all of the transistors do not have shorts.

These are the transistors heating up:

View attachment 26553496

https://drive.google.com/file/d/0B_chMLDhPolROGZBYW5QOFpLdlk/view?usp=sharing

https://drive.google.com/file/d/0B_chMLDhPolRVm5lMVd2NEZlOFk/view?usp=sharing

Any idea of what could be wrong with this amp?

Thanks,

Phil.

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[Buck 5,000+ posts]

So what exactly are you trying to figure out?

 

[erod856 10+ year member]

Buy new amp

 

[The_big_dill]

So what exactly are you trying to figure out?

Just trying to repair this amplifier, do my findings not point to any specific component being the problem? I would rather fix it than junk it.

 

[wew lad 5,000+ posts]

Depending on the amplifier you could different components going bad causing excess leakage or draw which is causing those transistors to heat up.

Most of the time it's cheaper to get a new amp with often better specs than pay to repair the amp. You'll get more help from people who work with actual circuits on diymobileaudio but don't expect much help. Not a lot of people know that trade.