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  • avatar zaken1 05/02/09 3:08 pm PST

    This distributor uses a light beam produced by an LED (which is like a small light bulb), to shine light on a photosensor (an electronic device which responds to either light, or the absence of light). The LED and photosensor are called "optics' because they use visible light to do their thing. There is a rotating shutter wheel with alternating open slots and solid spaces, which is located between the LED and the photosensor. The solid spaces on the shutter wheel are referred to as "towers." The shutter wheel is a round plastic wheel, maybe an inch in height and a few inches in diameter, with 8 narrow slots in it (if it were used for an 8 cylinder engine; or 6 slots for a 6 cylinder engine, etc.).

    When an open slot in the shutter wheel lines up between the LED and the photosensor, the light shines through the slot to the photosensor, and the sensor signals the module to turn off the charging current through the coil, which then produces a spark. But when a tower in the shutter wheel blocks the light beam from the LED; the photosensor senses there is no light, and signals the electronics in the module to turn on the charging current through the coil; so that it will be ready to produce the next spark.

    This sequence of charging the coil and then interrupting the charging current to produce sparks is repeated thousands of times a second while the engine is running. And that stream of sparks is passed in the proper sequence to the spark plugs in the engine's cylinders, through the distributor cap, rotor, and plug wires.

    What the instructions are saying is for you to measure the voltage at the coil negative terminal with a digital multimeter. They want to know what the voltage is at that point when the charging current through the coil is turned on (when the light beam is blocked). If you measure 2 volts or less at the coil's negative terminal when the light beam is blocked; this test verifies that the module is conducting charging current as it is designed to do. If there was a bad ground connection at the distributor or module, or a defective component in the module; the voltage would be higher than 2 volts at the test point when the light beam was blocked.

    If one of the towers in the shutter wheel happened to be blocking the light beam when you wanted to make this test; you wouldn't have to do anything else to block the light beam. But if there happened to be an open slot in the shutter between the LED and the photosensor at that time; you would have to block the beam with a piece of plastic, or some other material which light cannot pass through, in order to make the test.

Answers

  • karjunkie 05/02/09 11:45 am PST

    This Mallory Unilite distributor gives you accurate maintenance free ignition timing using photo optics. Instead of an old-fashioned points system the Unilite has a photo optic LED triggering system that never varies or wears out. The LED is inside the distributor under the distributor cap.

  • zaken1 05/02/09 3:08 pm PST

    This distributor uses a light beam produced by an LED (which is like a small light bulb), to shine light on a photosensor (an electronic device which responds to either light, or the absence of light). The LED and photosensor are called "optics' because they use visible light to do their thing. There is a rotating shutter wheel with alternating open slots and solid spaces, which is located between the LED and the photosensor. The solid spaces on the shutter wheel are referred to as "towers." The shutter wheel is a round plastic wheel, maybe an inch in height and a few inches in diameter, with 8 narrow slots in it (if it were used for an 8 cylinder engine; or 6 slots for a 6 cylinder engine, etc.).

    When an open slot in the shutter wheel lines up between the LED and the photosensor, the light shines through the slot to the photosensor, and the sensor signals the module to turn off the charging current through the coil, which then produces a spark. But when a tower in the shutter wheel blocks the light beam from the LED; the photosensor senses there is no light, and signals the electronics in the module to turn on the charging current through the coil; so that it will be ready to produce the next spark.

    This sequence of charging the coil and then interrupting the charging current to produce sparks is repeated thousands of times a second while the engine is running. And that stream of sparks is passed in the proper sequence to the spark plugs in the engine's cylinders, through the distributor cap, rotor, and plug wires.

    What the instructions are saying is for you to measure the voltage at the coil negative terminal with a digital multimeter. They want to know what the voltage is at that point when the charging current through the coil is turned on (when the light beam is blocked). If you measure 2 volts or less at the coil's negative terminal when the light beam is blocked; this test verifies that the module is conducting charging current as it is designed to do. If there was a bad ground connection at the distributor or module, or a defective component in the module; the voltage would be higher than 2 volts at the test point when the light beam was blocked.

    If one of the towers in the shutter wheel happened to be blocking the light beam when you wanted to make this test; you wouldn't have to do anything else to block the light beam. But if there happened to be an open slot in the shutter between the LED and the photosensor at that time; you would have to block the beam with a piece of plastic, or some other material which light cannot pass through, in order to make the test.

  • walt69 05/02/09 4:04 pm PST

    Thanks for your answer zaken1 I have this question posted on half a dozen forums and your answer is the first intelligent reply I have recieved.

  • zaken1 05/02/09 11:35 pm PST

    Thank you for the complement! Because I have been developing my own ignition system for the last 35 years; I just happen to have gone far more deeply into ignition theory and have become more familiar with currently available ignition systems that most other people.

    But, to be fair; there are relatively few Mallory systems out there. And Mallory is one of the only companies that uses an optically triggered system. Most of the OEMs and aftermarket manufacturers use magnetically triggered systems. That's why so few people can offer a good answer to your question.

  • walt69 05/03/09 9:21 am PST

    zaken1, "Mallory is one of the only companies that uses an optically triggered system. Most of the OEMs and aftermarket manufacturers use magnetically triggered systems."

    What is your opinion between the two? In your opinion do you think one is better / more reliable than the other? Can you recomend a good mechanical dist. if you belive that a mechanical is better than optic.
    Thanks

  • zaken1 05/03/09 11:49 am PST

    walt69: Mallory Unilite (the predecessor to this system) ignitions were not able to handle as much power as competitive systems. And Mallory electronics have been known to not be quite as reliable as others. I've had several failures with both Mallory coils and with their electronic controls.

    But in order to recommend a distributor or ignition system for you; I'd need to know what kind of motor you have, what modifications it has (if any), full details about any ignition system changes, the present coil type, whether you intend to use this engine in racing, daily driving, and what you would like to achieve by installing an aftermarket distributor. It would also be helpful to have a sense of whether you want to spend as little as possible; or whether money is not a big concern.

  • walt69 05/04/09 8:38 am PST

    zaken1, I have a 1969 corvette with a crate 350 /390hp. eng. Holley 650 carb, Edelbrock heads and performer intake manifold and headers.No other mods. I seldom drive this vehicle and never race. The Mallory dist. I have installed now was already in there when I purchased the car. I'm happy with it if it is a reliable unit. If I replace it I need to replace it with a dist. with a tach drive. I may sell the car so I do'nt want to spend a lot if I replace it.
    Thanks.

  • zaken1 05/04/09 2:49 pm PST

    Thanks for the details. I don't see a reason you would need to change the distributor. It is not known to be unreliable. I just said there have been some failures with other Mallory products I have owned; and the Unilite module cannot handle as much power as some other competitive products. But since you are not into racing, and do not need the most possible ignition power; I would just stay with it.

    Joel

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