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Electrical / audio puzzlement


nicks90
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Wondering if anyone could help me identify a strange electrical / audio issue i am having with my 300tdi 90.

as it stands at the moment the electrical system is completely standard and all of it works!!! I now, screwed it now.

It is also fitted with a 250watt amp and some rather nice speakers in the back. This is powered directly off the battery and the amp is turned on by some black 'exciter wire' that comes from the stereo, so the amp only powers on when the stereo does. Wiring to the stereo is all standard wiring too - other than none of the speaker wires are utilised, as the speakers are all connected to the amp.

Problem i have suddenly started to experience is this - if i subject alot of load on the electrical system, I get popping noises from the speakers/amp or in extreme cases the amp turns off!

For instance,

1) lights on, blower on full, rear demist on, wipers on and stereo on. Continuous crackle or the amp turns off

2) lights on, blower on full, wipers on part time. every time wiper starts its stroke - pop pop.

3) Blower on full, rear demist on, wipers on part time, as number 2.

turn some of the other electricals off and the popping and cutting out of the speakers stops!

I;ve checked my alternator and when at idle its pushing 14.2v across the battery and this rises to 14.4v at fast idle. So the alternator seems to be fine. So i cant understand why all of a sudden its started to cut out the stereo speakers/amp under heavy load. the least it could do is not interrupt my metallica session and cut out the bloody lights or something equally as unimportant (JOKE!!! well.......)

any idea why its started to do this, or am I looking at a goosed alt or maybe the battery is going weak?

cheers

Nick (please shout loudly, i;m deaf) C

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I don't think the main problem is electrical noise. Though, you may have noise issues as well.

More likely just that the voltage the amp is seeing is too low - which is causing it to drop-out.

How is the amp earthed? Does the earth go straight back to the battery or is is via the bodywork?

Measure the voltage at the amp to see how it varies with the different electrical loads switched on.

If you find yourself running new earths, run one directly from the battery -ve to one of the starter motor mounting bolts. This ensures that the engine and thus Alternator have a good earth rather than via an earth strap engine to chassis and another one chassis to battery.

Si

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the amp is connected + and - to the battery with properly thick cables from a reputable audio specialist and other than when there is alot of other electrical load, it all works faultlessly.

would a dying battery cause this? Reason I ask is that my motor always starts on the first full compression cycle after using the glowplugs - so i havent noticed anything untoward. However upon questionning the wife (who never waits for the glow plug light to go out) she said the other day when it was frosty, the engine turned over very slowly for about 5 turns before catching and she was surprised it fired!

So could a poorly battery cause this?

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As Simon says, measure the voltage at the amp to see what's going on there first.

I would also try disconnecting the audio input from the amp and see if you still get the "popping" noises, this will tell you if the electrical noise is coming down the power feed or the signal feed from the head unit.

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