The main possibilities involving the vehicle are 1) a charging system defect, or 2) recent vehicle mechanical service. I would most highly suspect the installation. By wiring the system on a table where the only connections to the vehicle are directly to the battery and speakers, you will narrow the field down to the charging system or the installation. If the system plays fine on the table, the installation is at fault. If the same muting occurs, you likely have a charging system problem.
Q I have a '94 Mercedes S320, with a McIntosh (the longest one) amp, and a Sony head unit that has a video input. I have connected a PlayStation, portable DVD, and portable VCR using a 12 to 114 V converter. I get noise when I turn on the headlights. It's not a whining noise like an alternator but more like buzzing noise that disappears if I turn off the headlights. The rest of the system is free of the noise.Name withheldvia the Internet
A As soon as a voltage converter is mentioned, many veteran installers immediately lock onto it as the cause of all noise problems. This stems from experiences dealing with "other voltage" vehicles like several vintage British cars that run either positive ground electrical systems, or like Volkswagens that had 6-volt systems, or both. The Toyota Land Cruiser with its 24-volt system was also a repeat nightmare for unfamiliar installers. White Freightliner highway tractors with its positive ground system were popular stereo and communications platforms, but you had only two installation choices: use a converter or guarantee an electrical fire!
The obvious clue in your scenario is that the noise occurs only when the headlights are on. If I understand your description correctly, the noise is also limited to the video-based products, namely the PlayStation, and the VCR. This would normally leave a troubleshooter with a primary suspicion (the car) and a secondary suspicion (the video equipment).
Some installers would simply try to block the noise by using a line filter on the converter of the video products. This can often stop the symptom, but since the problem is still there, the noise can reappear either in the units already filtered or in other equipment.
The preferred method would be to suppress the noise at its source. What is the source? My money is on either a Daytime Running Light (DRL) system or a pulse dimmer unit. The former allows the headlights to remain on at all times while driving. Note: safety advocates point out that, especially in bright daylight, a pair of headlights stands out in the distance and reduces head on collisions.
The life span of the headlight elements would be dramatically shortened if there were not a way to ease the strain for constantly operating. The DRL module provides around half of the normal power to the headlights during the daytime by pulsating the current, which also produces noise. In this case, the noise would occur with the headlights OFF.
With the headlights ON, the instrument panel lights are controlled by a pulsating dimmer circuit that behaves in a similar fashion to the running lights. By locating this module, you can suppress the noise at the source by using a noise filter.
Please send questions to:Car Audio and Electronicsc/o Troubleshooting774 S. Placentia AvePlacentia, CA 92870e-mail: techpanel@mcmullenargus.com
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