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Thread: bench testing Bosch ignition exciters

  1. #1
    Join Date
    23.11.2018
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    Gibsons, BC, Canada
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    81 MHR
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    Default bench testing Bosch ignition exciters

    Hi folks: Anyone here have any idea how to bench test Bosch ignition exciters? I'm working on an 81 MHR and want to ensure my electronics are sound. I've found bench tests for the regulator but not the exciters.

  2. #2
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    14.06.2014
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    The workshop manual states that the resistance between the terminals should be 220 OHMS, then it says to 'connect the two resistances with the Ohmmeter, the resistance should be 0.9'. I've no idea what they are talking about.

  3. #3
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    19.12.2005
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    Quote Originally Posted by duccout View Post
    The workshop manual states that the resistance between the terminals should be 220 OHMS, then it says to 'connect the two resistances with the Ohmmeter, the resistance should be 0.9'. I've no idea what they are talking about.
    The workshop manual in fact says that the resistance of the pickups should be 220Ω and that the resistors should measure 0.9Ω. You will find it very difficult to measure such a low resistance with a meter but as long as they are not open circuit they are probably ok.
    It says nothing about the Bosch igniters I'll see if I can find out anything.

    Click image for larger version

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  4. #4
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    I've had a look at the circuit for the ignition system which I've drawn in the attached diagram.
    Click image for larger version

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    It shouldn't be hard to rig this up on the bench with a coil and pickup attached. 12v is supplied to the ignitor and through the resistor to the coil. The ignitor has a ground connection and the coil is grounded through the ignitor. It breaks this ground circuit to create the spark.
    With the power and ground connected you should get a spark if you wave a big lump of metal like a spanner close to the pick up. If it doesn't the ignitor is probably faulty.
    Also, you should get a spark when the power is shut off and magnetic field in the coil collapses.

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  5. #5
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    23.11.2018
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    Thanks guys. I guess the easiest way to test is to hook each of my exciters up and test them on the bike; I've got six in total but I think two are from a Laverda; they have a different part number (1 217 280 042) but are otherwise identical to my originals (1 217 280 034). Now I need a battery....

  6. #6
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    I believe that the Laverda units have a different ignition advance curve from the Ducati ones, so may not be entirely interchangeable.
    Another rough check on the unit would be to measure the resistance between the the orange/black coil wire and the black ground connection. As it is a semiconductor device I would expect a high resistance in one direction, swap the leads round and you should see a low resistance in the other direction.

    And I hope your pickup wires are in better condition than the ones from my Pantah were -

    Last edited by Derek; 25.11.2018 at 10:13 AM.

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  7. #7
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    I plan to pull the casings and check both sides' wires. The regulator ends of the alternator wires is bad; the insulation is hard and easily broken off. I'm guessing that this is due to localized high temperature. I'll know more when I expose more wire and start effecting a repair.

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