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MG MGB Technical - Radio Sound Cuts Out when Engine is On

Hi all.

Installed a Kenwood CD Player. CD plays flawlessly when engine is not running. When the car starts, the sound cuts out /stutters. This happens at low and high rpms. Radio power is wired to green/white wire and to the lighter for memory, and directly grounded to car with a screw. I have a voltmeter and I am getting proper charge at 14v at 2k rpm

Tried the following but no success:
-Wired directly to fuse box
-Wired directly to alternator
-Wired directly to battery (slight improvement)

Alternator was installed recently (delco).

What is puzzling is that it plays ok when the engine is not running. What else can I try? Could it be the player?

Thanks.
NV Valera

You probably need a capacitor (condenser) between the green white wire as close to the radio as possible and the ground. There is probably noise from the ignition on the line upsetting the stereo. You won't see it on a standard meter though.

What I am not sure about is if you need a special condenser or if you can use one like the one in the coil. I would start with one of them (it won't hurt at all) between the ground (body) and the power wire to the stereo.

I don't have a radio in my car at all so I don't have this problem!

Simon
Simon Jansen

I'm wondering if there's a glass tube in-line fuse with a dodgy
element or contacts in the CD player (or harness)?
Daniel Wong

The noise suppression capacitors Simon refers to are normally to suppress high-frequency noise which causes hissing buzzing or crackling on a radio and are installed as close to the *sources* of such noise as possible e.g. coil, instrument voltage stabiliser, pump etc. If the cause *is* electrical it sounds to me like the peturbations in the supply are very much larger than one of those capacitors would suppress, a much larger capacitance might help, but the point is it shouldn't be needed if the voltage supply is as it should be. If the unit is only a CD player, or it is only the CD that is being affected, then it's possible mechanical vibration is the cause, it depends if it has a 'skip memory' and how effective it is. I've already suggested to NV that he tries powering the unit from an external source while his own engine is running to eliminate electrical interference, and to remove the unit from the console and cushion it while being powered from the car with the engine running to eliminate vibration. It should also be tested in other cars, as it may just be a bad unit. If it proves to be electrical and the unit works fine in other cars there may be another source of very high noise in NVs car, like bad connections between the battery, body and engine. All things being equal, the car should not generate noise or vibration bad enough to affect a radio or CD, and a radio or CD should not be sensitive enough to be affected by *normal* mechanical and electrical effects.
Paul Hunt

Update: I took the player out, held it in my hands and the same result. The symptom is the same if I play FM radio so I doubt it's due to vibration. I will take it all out and see if it works outside the car. This is weird. Thanks.

-Napoleon
NV Valera

Ah, ignore my comment and go by what Paul says! That's what you get from trying to reply quickly when you should be working :)

Simon
Simon Jansen

Solved! I replaced my worn out spark plug wires and the radio no longer cuts out, plays perfectly! Thanks.

-Napoleon
NV Valera

This thread was discussed between 09/04/2009 and 12/04/2009

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