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Need help with halogen task light problem!

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  • Need help with halogen task light problem!


    Maybe someone here can help me!

    I have an Electrix Model 7750 halogen light on my lathe and it stopped working. At first I thought it was the bulb so I replaced it...still didn't work. Then I bought a new transformer, replaced it, and still no go. There's nothing else in it to replace!

    Here are some facts:

    1.) Tested continuity thru switch - okay, works correctly.
    2.) Tested for shorts to ground thru wires in arm from base to light head - okay.
    3.) Tested voltage to primary at transformer - 124.6VAC.
    4.) Tested voltage on secondary of transformer - should read ~ 11.5VAC, I read ZERO.
    5.) Tested bulb for continuity, okay.
    6.) Tested for continuity across primary - no continuity.
    7.) Tested for continuity across secondary - yes continuity.

    Let me explain something a little better. The transformer, or what I call a transformer, has an input of 120VAC and an output of 11.5VAC listed on the case. But is this a transformer or something else? It says on the case that it has an operating frequency > 20KHz. Is this why I can't get a voltage reading on the secondary???

    BTW, I replaced all parts with Electrix parts purchased thru Grainger, so compatibilty should not be a problem.

    If anyone can help me I sure would appreciate it. I contacted Electrix about the problem and they said they would refer it to their tech department an get right back to me. I haven't heard from them in a week.

    What am I missing or doing wrong?


    [This message has been edited by Mike Burdick (edited 03-20-2003).]

  • #2
    As far as that unit, dunno what is wrong, I'm not there.

    But, some of the halogen lights use a "switch mode power supply" meaning that there is electronic stuff that passes the power thru at a high frequency. that would be your 20 kHz label.

    The advantage is that

    1, the transformer is much smaller and lighter for high frequency.
    2) a lossless dimming system can be used

    Others have a regular transformer and a slightly different dimming system.

    Since the parts are new, that leaves the connections.................?


    • #3

      What you say makes a lot of sense. From the sound of it I must have mis-wired the replacement parts - even though it seemed so simple. Maybe I can get Electrix to send me a wire diagram.

      Thanks, somehow I have this "gut" feeling you're right so tomorrow I'll re-study the situation.


      [This message has been edited by Mike Burdick (edited 03-20-2003).]


      • #4
        I going to assume that you replaced the transformer as a module, that has writing on it saying it operates at 20 khz. If that's the case, it won't show continuity on the primary because it needs to oscillate before any juice can flow. Testing with a meter won't start it up, so no continuity, except maybe for a second or two, as the internal capacitor charges from the meter. You've replaced the entire power supply, so as long as you don't have a short on the secondary, there's no reason for it to not work. It's defective, or wired in backwards, in which case, it's defective now. If indeed you have it wired correctly, then you know which is the secondary, it's the only pair of wires with continuity, a very low reading, less than 1 ohm.. Don't be fooled by reading the resistance of the bulb, still connected to the unit.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


        • #5

          I was very careful about wiring the primary to the 120VAC - that I was sure of! It is very clearly marked on the module.

          I was also very careful to install it back into the circuit just like the old one so I'm pretty sure everything is wired correct. I guess that only leaves the bulb...

          Thank you for the explanation of how the module works and also for the help. I sure do appreciate it!



          • #6

            Continuity checks are great but they don't prove it's going to work. They just find certain specific problems. I would start at the secondary of the transformer where you report no voltage. How did you measure this? Meter? Scope? If it's really operating at 20 kHz, they may not rectify that to DC on the "transformer" output. It may be a 20,000 Hz AC output. Many inexpensive meters will not indicate anything at that high frequency. They are calibrated at the 60 Hz. power line frequency and may only extend to a few hundred Hz.

            Check your new bulb for continunity with the meter and replace it if it's bad. Then use a temporary hookup directly from the output of the "transformer" with clip leads or separate wires to the bulb. No shock hazard here if it's 11 volts so you can just hold the wires on the bulb for a second or less. BUT BEWARE OF THE HEAT GENERATED BY THE BULB. Any 12 volt automotive bulb of equal or lesser wattage could be used to avoid the high heat of a halogen bulb. If it works then you have a wiring problem. If it doesn't and you still have 110 volts on the primary, then the "transformer" is bad. A small percentage of "new" parts will be bad. Not may, WILL.

            If it is a wiring problem (sounds like it's not), it could be either an "open" or a "short". In this case, continunity testing is called for. Sounds like you know how to do that.

            Another possibility is a defective socket. If the bulb is not making proper contact in the socket it just won't work. Halogen lamps tend to be hot and that can deteriorate the socket. I see this A LOT in TV studio lights. Look for corosiion. look for a center contact that's lost it's springeness. Inserting the bulb may cause a short. You may have to replace the socket.

            Note: This "transformer" sounds like it's not actually just a transformer but instead, an electronic voltage converter module. Not being familiar with the line of lamps, it's hard to know what form the output of this module is supposed to be. A simple device like a filiment style light bulb will operate on DC, low frequency AC, higher frequency AC like 20 kHz and even on radio frequency voltages. A good bulb is a better indicator for the presence of this output voltage of unknown frequency than any meter as meters are definitely limited in their frequency response. A scope would also be a better choice.

            Paul A.

            Make it fit.
            You can't win and there is a penalty for trying!


            • #7
              Be pretty careful when messing with that when power is on. I would not guarantee that the bulb circuit is totally isolated from the line.

              Also, high frequency voltages don't act like low frequencies. You may get a burn or other undesirable effect from what would not be harmful at low frequencies.


              • #8
                Paul may have hit on the root of the problem, the bulb socket. I've seen several of those go bad, since the heat is so high. Had that problem just a few weeks ago.
                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-