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Author Topic: New whine in Received and transmitted audio...alternator going bad?  (Read 5926 times)
KB9WQJ
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« on: September 03, 2012, 04:42:30 PM »

  Hello all.  I have an FT-7800 dual band Yaesu in my Ford Focus.  Unit is under passenger seat, head mounted to dash. Antenna NMO mount in middle of trunk lid.  Has been very satisfactory for a few years now.
   This Friday just past, I noticed a whine in my received audio on both 2m and UHF.  It's frequency veried with engine RPMs.  This has appeared totally out of the blue.  I was able to determine that it is also going out on my transmitted audio.
  So what do I look into? I already made sure that everything is hooked together tightly and my ground is good, etc.  Is this a sign my alternator is going bad?  What are my steps to determine and mitigate this?

  Thanks.
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W8JX
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« Reply #1 on: September 03, 2012, 06:17:50 PM »

You may have lost a output diode. The fact it happened suddenly tends to suggest this.  There are 6 of them.  Modern alternators are delta wound 3 phase output. 
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KB9WQJ
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« Reply #2 on: September 04, 2012, 03:39:47 AM »

I also forgot to mention that I noticed the flourescent display of the clock/radio randomly fluctuating in brightness (very slight difference).  I could not say for certain whether this was new behavior or if I was merely extra vigilant and looking for things.
  Thanks for the info.  The vehicle is older, I may change the alternator and see.
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K5LXP
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« Reply #3 on: September 04, 2012, 06:09:02 AM »

I noticed a whine in my received audio on both 2m and UHF.  It's frequency veried with engine RPMs.  ...  I already made sure that everything is hooked together tightly and my ground is good, etc.

Did you check the grounds under the hood too (engine, battery, alternator, transmission, etc)?

A bad diode in an alternator is readily visible with an o-scope.  It could be that, but I'd suspect a failing ground first.


Mark K5LXP
Albuquerque, NM
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KB4QAA
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« Reply #4 on: September 04, 2012, 01:22:22 PM »

-Disconnect the antenna with the engine running.

-If the noise goes away it is being radiated over the air (and is NOT the alternator)
-If the signal remains, then it is coming through the power line and MAY be the alternator
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AJ3O
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« Reply #5 on: September 04, 2012, 02:56:30 PM »

Check your spark plug wires. Run the engine at night in the dark and look for any glowing or sparks. If nothing is visible, get an old handheld AM radio and tune it for static or white noise. Put it close to the spark plug wires while the engine is running and listen for the whine on the radio. Where it gets louder is where the culprit is. This works for the alternator also so take your time and move it over everything under the  hood. BE VERY CAREFUL not to get burned or "bitten" by the belts or anything else that moves.

This works as a quick check and should get you closer to the problem.
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W8JX
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« Reply #6 on: September 04, 2012, 03:14:54 PM »

Never seen plug wires cause whine.
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KI4SDY
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« Reply #7 on: September 04, 2012, 05:10:14 PM »

A bad spark plug or wire connection usually makes a continuous popping sound.  Wink
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NO2A
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« Reply #8 on: September 05, 2012, 01:03:11 PM »

I doubt it`s your alternator. A simple voltage check would tell. Fords are notorious for loose ground connections. I have the same problem in my Mustang. I get whine on the car radio and ignition buzz on 2m receive only. It could be a diode as well. Most likely ground is loose somewhere.
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W8JX
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« Reply #9 on: September 05, 2012, 01:53:06 PM »

I doubt it`s your alternator. A simple voltage check would tell. Fords are notorious for loose ground connections. I have the same problem in my Mustang. I get whine on the car radio and ignition buzz on 2m receive only. It could be a diode as well. Most likely ground is loose somewhere.

A few years ago I suddenly developed a whine in my electronics in truck and it was alternator. I also got some flicker due to reduced output under load and regulation issues due to failure.
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K7RBW
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« Reply #10 on: September 06, 2012, 06:52:08 AM »

You should be able to take your car to any auto parts store and have them test the alternator. They usually do it for free and it just takes a few minutes. That should also identify any grounding problems (maybe), but at least it's a quick check to help get you started in the right direction.
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KB9WQJ
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« Reply #11 on: September 06, 2012, 07:05:15 AM »

  Does the auto parts store have the ability to determine if one of the output diodes has gone bad without the whole thing failing?  If I can get a o-scope on it what do I look for?...Alternating current where there should be none?

  Thanks for everyone's replies.  I appreciate them.

  Mike KB9WQJ
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W8JX
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« Reply #12 on: September 06, 2012, 07:39:53 AM »

  Does the auto parts store have the ability to determine if one of the output diodes has gone bad without the whole thing failing?  If I can get a o-scope on it what do I look for?...Alternating current where there should be none?

  Thanks for everyone's replies.  I appreciate them.

  Mike KB9WQJ


Car parts store can only load test them. With a diode out there will be some reduction in output but may not show unless more than one diode has failed. A scope would show it.
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K0BG
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« Reply #13 on: September 07, 2012, 07:57:34 AM »

I'll lay odds it isn't an alternator diode. Instead, it is a ground loop, and as Mark alluded to, it is time to check all of the ground connections.
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KB9WQJ
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« Reply #14 on: September 07, 2012, 08:03:09 AM »

  Re: ground connections.  Is there a list of them somewhere?  I own the Chilton's book for my car.

  Thanks, Mike
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