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Thursday, October 11, 2012

This Hum Is Driving Me Crazy! - Radio Noise Exorcised!

VHS! (The DVD and Satellite is in the Left Compartment)
    A while back I replaced my entire entertainment system and re-wired all the video and audio lines. I figured I could add some "doohickys" (toroidal chokes) to eliminate the horrible hum whenever I watched anything. Needless to say, it didn't work. I like watching (and making) Television Shows and Movies, so I really needed this to work well. After exhausting all the possibilities (So I thought) I gave up. It's always been at the back of my mind though. There was a small problem with the remote control for my VHS(!) VCR. I don't use it very often, but I like when everything works. I managed to locate a "same-model" replacement and was wiring it in when I realized, NO HUM!!?!
What the.....OK, back to square one.

Oh, The Horror!
The RV is wired with grounded outlets and a few GFCI dual outlets from front to back. The ONLY difference was that the new VCR I was testing was plugged into another outlet. This wasn't the one in the entertainment compartment. I really believed the entire RV was wired properly. Be careful what you believe! It Was Not True!  I pulled everything out of the right side entertainment compartment and found, to my horror, that the outlet the power strip was plugged into was actually a cut-off, UN-GROUNDED, el-cheapo extension cord. Someone had cut off one end and wired it into a grounded outlet box. Obviously, this is a BAD practice. Without a ground, you can easily (and likely) get a hum either heard through your speakers or viewed on your screen, not to mention the fact it is BAD to have anything not properly grounded. In this case some expensive stuff was connected to sub-standard wiring. We all know that fire is a real danger in an RV. Since all of this was well hidden it would probably be too late when you smelled/saw the smoke or flame. Always better to be safe!
Wiring Like A Snake Nest

Of course, to get the old extension cord out and the new Romex cable wired in, would take a lot of work. The odd thing here is someone spent a lot of time really doing a spectacular job of running the chopped extension cord wire. It had slack where it needed it, cable stays (the loop ones you screw into wood) every few feet and at corners where the wire bent and they made a carpet and Velcro cover for the A pillar so you couldn't see the wire run at all. With all that work you'd think they'd use a grounded cord, at least!!

Ah well.

New CORRECT Box Without Cover
Once the Romex cable was run from the upper compartment to below the dash (at the passenger's knee) where there is a dual grounded oulet box. I turned off the main circuit breaker and wired the new grounded wire into the existing dual grounded outlet box. Just like you would do at home. At the other end I had a plastic outlet box and grounded outlet with a pretty cover. This was wired up next, making sure the wires went to the correct terminals. I put a healthy amount of sticky back Velcro (Hook side only) on the back of the box and affixed it to the carpeted compartment back.  You know, sometimes I really LIKE that everything in my RV has carpet on it!!

Once everything was loaded back into the overhead compartment, I re-re-re-wired the components, crossed my fingers, and turned it all on. Success! No more Hum. I don't believe I'll miss it at all.

Be Seeing You...Down The Road

Rich "The Wanderman"
www.thewanderman.com





2 comments:

  1. when running speaker wire, consider using coax. The braid act as a shield as well as the neutral.

    ReplyDelete
    Replies
    1. Anon,
      Often, coax is too thick to run to speakers. Many places in RV's for cable runs are very small and narrow.

      The braid WILL act as shielding, but that type of interference isn't the culprit here. Rather the 60Hz hum from the AC power system.

      Rich "The Wanderman"

      Delete

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