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Multi-lamp fluorescent sign ballast mystery

Discussion in 'Lighting' started by Chuck, Nov 16, 2008.

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  1. Chuck

    Chuck Guest

    I am helping a friend who owns a restaurant to repair a large marquee sign
    in his front parking lot. The sign was working fine for the last 3 years
    until recently. The sign uses two separate horizontal banks of 5 linear 72"
    (F72T12/D/HO) lamps per sign ballast. The pin style is recessed double
    contact. The input voltage is 120VAC. The label on the sign ballast has
    aged but looks like its a Rapid Start - Magnetic, Valmont 6G3959WF. I
    think this is a 4 lamp ballast (not a 5 lamp). There are a total of two
    ballasts, one for each bank of five lamps, for a total of ten lamps. One
    bank of five lamps works just fine. However, on the other set of five, only
    one lamp, the one at the bottom physically closest to the ballast lights up.
    All of the lamps have been confirmed to work by removing them one at a time
    and testing them in the working lowest socket. I now need to troubleshoot
    this bank of lamps while standing on top of a 12ft step ladder in the middle
    of a parking lot.

    Troubleshooting Questions:
    - Since one lamp still works, can the ballast be considered 100% good?

    Chuck
     
  2. JohnR66

    JohnR66 Guest

    5 Lamps on 4 lamp ballast? Something screwy here. Need to see the wiring.
     
  3. Chuck

    Chuck Guest

    Vic,
    I will be taking my second look at the lamps and ballast tomorrow weather
    permitting. I will open up the wire channel hats and will count the
    wires/colors pairs then for a positive identification. I think it is a 4
    lamp ballast only because of the ballast label that reads 6G3959WF which
    happens to be a 4 lamp sign ballast per (
    http://www.advancetransformer.com/uploads/resources/CR_SignBallast.pdf ).
    Will get back to this thread shortly thereafter. Thanks.

    Chuck
     
  4. Chuck

    Chuck Guest

    I replaced the single known-bad bulb in the unlit bank of four and..... they
    all lit up. The single lamp on the bottom that was always lit was wired to
    another ballast (I overlooked) from the lamp bank on the other side. In
    conclusion, there were a total of three ballasts, two four lamp sign
    ballasts and one two lamp sign ballast. Problem solved. Thanks for helping
    me think this through.
     
  5. I don't have any references I can look up (I've been out of town for
    some time), but I woudl venture to guess that this is a speial class of
    ballasts called sign ballasts. Often they will be rated in terms of
    total length of lamps, rather than number of lamps. The facttthhat the
    lamps involved are HO types is also at least suggestive of this.

    Jeff Waymouth
     
  6. Chuck

    Chuck Guest

    I replaced the single known-bad bulb in the unlit bank of four and..... they
    all lit up. The single lamp on the bottom that was always lit was wired to
    another ballast (I overlooked) from the lamp bank on the other side. In
    conclusion, there were a total of three ballasts, two four lamp sign
    ballasts and one two lamp sign ballast. Problem solved. Thanks for helping
    me think this through.
     
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