125 Sport electrical problems
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Thread: 125 Sport electrical problems

  1. #1
    Junior Member
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    Ricardo Ramalho
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    125 Sport electrical problems

    Hello Everyone
    I'm the proud owner of a 125 Sport (which is essentially the same as a 2C techically). I've been having some gremlins with the electrical part. I'll try to describe it as well as I can:
    There are two groups of wires out of the alternator; one for the ignition circuit and the other for charging the battery/lights/etc.
    I'm getting a parasite current at the battery terminals as soon as the bike starts. I can't measure it properly with a tester because it appears to be AC, but with an inconstant frequency. It appears the frequency and voltage vary as the engine revs faster or slower.
    This happens even if I unplug the wires from the charging circuit and the rectifier unit - this means it comes from the ignition circuit.
    Now, at first, I suspected I had a faulty CDI. I managed to take off the paste that was covering the electronics, revealing a fairly simple circuit of five diodes, two capacitors and a thyristor. I thought a burnt diode would be the culprit, replaced virtually all components and tested the CDI. The behaviour is exactly the same. At least this part is a win, because now I can draw a schematic for the CDI and post it here; I'm sure someone will find it useful.
    The bad news is that the problem persists and the only other part capable of creating this type of current are the ignition coils. I used a tester and got about 1 ohm for the primary winding and 3.1K for the secondary winding. This goes for both coils. Although these values seem normal and they don't seem to be shorted to the outer casing, and bearing in mind that the wiring seems ok, with no shorts do the earth, does any of you have an idea of what may be causing the malfunction? Did anything similar happen to any of you?
    Thank you so much for your help!

    Ricardo
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  2. #2
    Senior Member R Powell's Avatar
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    Richard Powell
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    Hi Ricardo,
    Welcome to the Benelli forum I have a 125 sport and like you say it is similar to the 2c.
    the electronic ignition is feed directly from the flywheel and is separate from the lighting. I suggest that maybe someone has connected the ignition switch wrong as this is the only switch to have both circuits! The other problem might be a short circuit in the wiring loom bridging electric from the ignition system to the battery terminals.
    i would be interested to see how you repaired the electronic ignition box? As the used to be unreliable!
    good luck

    Richard

  3. #3
    Junior Member
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    The ignition switch does what is supposed to: when turned on it connects the battery and unearths the positive from the coils. I can't find a damn short on the wiring!

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    Senior Member DenH's Avatar
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    DENIS
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    hi ricardo, if you havent already done this,check all the earth points are really clean and bright,its an old bike and its italian

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    Senior Member ferret's Avatar
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    Ricardo ,there must be a short from the ignition circuit if you have ac voltage at the battery even with the charging system disconnected .If there is a break in the loom i would suggest looking around the head stock area first as the shielding is a bit brittle and also the wires tended to chafe in this area . A faulty ignition switch could cause the same issue .

  7. #6
    Junior Member
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    Hi
    Thank you all for the suggestions. It must be a short; I must check the loom and look for it. The ignition switch seems to be working properly though. I'm getting out of ideas....
    I'll keep you updated. I still need to draw the schematic for the CDI and post it.
    Cheers!

  8. #7
    Senior Member R Powell's Avatar
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    Richard Powell
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    Hi Ricardo,
    This is just a thought but when cables run close together a small current May be induced in surrounding cables. This current is very small and does not effect the other circuit from running correctly.Try measuring it with a multimeter on AC 0/10 volt scale if it's less than 1 volt I would not worry.

  9. #8
    Junior Member
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    Ricardo Ramalho
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    Hi
    First of all, I'm sorry for the late reply.
    I sorted out the problem. Turns out the current I was reading was a parasite current which did not affect the electrics. It all came down to a faulty rectifier unit. I do have a spare original (which I tried). It didn't work and the behaviour was the same - a frend of mine who's an expert in electronics couldn't find a malfunction on that rectifier. I did a bit of research and found out that Boyer Bransden (Boyer Bransden Electronics Ltd) has something called a Powebox which delivers 12VDC without the need of a battery, so I did just that. I plugged a Powerbox directly between the alternator and the electrical implant and eliminated the battery. It works just fine!
    Of course I had to replace the horn, indicator relay and bulbs with 12V parts. I also replaced the bulbs with LEDs because the 6V alternator doesn't deliver 12V with the same power.
    But other than that it's been working really well and finally I get to ride my bike at night!
    I hope this info eventually helps someone
    Thanks for all the tips and help

    Ricardo125 Sport electrical problems-img_20150531_012629.jpg

  10. #9
    Junior Member
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    Ricardo Ramalho
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    And here's the diagram for the CDI125 Sport electrical problems-img_20150515_191145.jpg

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