Rear speaker saga: Part II ..... Hot speaker?!?!? - PeachParts Mercedes-Benz Forum

haasman · #1 05-01-2003, 12:30 AM

While testing to see what is wrong and why the rear speakers on the wagon, Rear Speakers Do Not Work

I had the left rear speaker hooked up, not touching anything and I grabbed it and to my surprise it was VERY warm. Not burning hot but really warm. There was no sound coming out of the speaker.

The radio was in CODE phase and I was waiting the 10 minutes because the first time I entered the code it didn't take.

Am I missing something here? Why would the speaker be so hot? It does test for continuity.

Haasman

PaulG · #2 05-01-2003, 06:08 AM

haasman,

If the speaker is not working, but is getting hot (if I read your posting correctly) there's probably some DC going to it.

Check with a meter to see if you can read any DC voltage across the speaker (check for AC as well, whilst you're at it)

My guess is that you'll find some voltage across the speaker. If you find say, 6v, the power dissipated in the speaker would be 9 watts, certainly enough to warm it up.

If this is the case, the most likely place for the volts to come from would be a failed output transistor in the power amp of the stereo.

haasman · #3 05-01-2003, 09:21 AM

Paul

I will check and report back. Thanks for your reply.

Haasman

haasman · #4 05-01-2003, 01:54 PM

I measured across the two speaker terminals at the left-rear speaker with it connected and the radio display saying: WAIT

I got about 10.7 volts average measurement.

What does this mean?!?! A failed output transistor in the power amp of the stereo?

Haasman

PaulG · #5 05-02-2003, 04:29 AM

You certainly shouldn't have that level of DC across the speaker......

Yes, it points to a failed (short circuit) power transistor in one half of the pair that drive the speaker output. You'll only know by checking the speaker with another power amp (or the whole stereo if it comes in one box).

10.7V is 28 watts dissipated in the speaker, so it has been working hard doing nothing, but the fact that it's warming up means that it's basically ok.

If the front speakers are working, then 90% of the stereo is ok, so it may be worth having it repaired, so long as the cost doesn't get too close to a new one.

You definately need to check all the speakers in the car by substituting another stereo (borrow one) before you start spending money, electrons are awkward bastards, and will give you false clues if they can.

haasman · #6 05-11-2003, 06:32 PM

Thanks for all the suggestions and help. Fixed the problem: Rear Speakers repaired

Haasman