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Help identifying SI board components?

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    Help identifying SI board components?

    1990 318i Lux Auto (UK).

    Pulled my instruments out to find out why my Inspection and other lamps are lit even though I've cleared them.

    1. Middle 'grain of wheat' bulb was blown - all I know is the two others measure 32 ohms but I can't see any markings to replace it. Anyone know the spec?
    2. The Sanyo lithium batteries give 2.9v each. Seems close enough to 3v for these not to need replacing, or to be the problem? Do they need replacing?
    3. Found a blown resistor/capacitor (it has two legs, that's all I can see) on the PCB. I can't identify it by markings, as it's melted, only by its position on the board. Is there a diagram that will help me replace it?

    Have reinstalled the instruments. Everything's working fine still except my Inspection light, which I'd like to clear and turn off. Any help much appreciated.

    #2
    1. most incandescent bulbs in this size will be fine and of similar impedance.
    2. on a 3v battery, a new one is 3.25v, so yeah your battery is more than dead. Dont consider voltage, consider current carrying capacity. New batteries can output around 900ma while your 30 year old batteries probably output 0.05A, essentially nothing. No such thing as a good 30 year old battery.
    3. typically a heavily melted part is a sign that there has been heavy electrical current running through the SI board and no heavy current should be running through it. You most likely have an SI board that can never be repaired.

    Lastly, never install new batteries (remember they have almost 2A combined) without changing all the transistors which also commonly fail. Ever heard of smacking the dash to get the gauges working again? That's failed transisors. Install new batts without transistors and it will permanent damage those sensitive microchips. About 15 years ago when I would repair SI board, I would only change the batteries and capacitors and noticed many Si boards were returning. Soon after, I started replacing all 30 caps, transistors and voltage regulators and we have repaired many thousands of SI boards over a decade without a single issue. IN the end, its not much for us to rebuild them and recommend going that route. You will find plenty of threads of guys who replace the batteries and it does not fix their issues, this is because they do not do a comprehensive job and end up damaging the si board.

    for the ultimate resource on SI boards see www.bavrest.com/technical-articles.html. Thanks
    Owner - Bavarian Restoration
    BMW and European Electronics Repair and Restoration
    www.BavRest.com
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