88 325 - schematic for antenna circuit board?

I've examined two failed power antenna units, both with roasted circuit boards. Any diagram for this out there? They were both roasted clear through between the heat synched power transistor sections-
middle of the board. You can jump the 12v motor and it will spool the antenna up or down so that works. Is there a simple circuit I could cobble to run this up and down on a signal from the ignition key? Board space is about 2.5inx1.5in. but I guess it could be outside the plastic antenna package just as well. It seems like you would need circuits to reverse the motor, to tell it when to stop spooling and to tell it whether it's already up or down. Ok, the spell check is complete I had zero errors. Thank you.
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I don't have a schematic... in my experience these things fail all the time because the cogged plastic rail that moves the antenna up and down gets chewed up. My bet is that you can ask someone to keep some scrapped units for you and you'll find a lot of them are electrically fine.
I'd check the power transistors and the emitter resistors, given the description you give. If all three of the power transistor pins are shorted together, you have found the original problem. Now you just have to find the collateral damage. --scott
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Very easiest way would be to just use a centre off non latching DPDT switch. If you must have an auto one buy a generic type (or get one from a scrapyard) and rob it of its electronics, if your one is a special for the car.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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London SW | To e-mail, change noise into sound.
Most likely, the transistor is being used as the switch.
Transistors have three terminals; 1) Base, 2) Collector, and 3) emitter. In this application, I'm going to guess that the power is tied to the collector and that when the transistor is forward biased, voltage and amperage flows from collector to emitter thereby providing power to the motor to run.
My suggestion is that you take the circuit board to an electronics repair shop. If my suspicions are correct about the electrical flow, just about any radio or TV shop should be able to make a reliable repair.
The thing you should be worried about is WHY the circuit became overloaded. Transistors are rated on the maximum amount of amperage capable of flowing through the transistor from collector to emitter. If the original transistor just wasn't able to withstand the normal amperage during the life of the vehicle, no problem; just replace the transistor with one able to withstand a larger amperage flow.
So, the first thing would be to measure the amperage flowing in the circuit to make a determination if the original transistor was of the correct size to handle the current. Take the measured amperage information with you when you transport the circuit board to your chosen repair shop. Make sure you take note of the "start-up" amperage and not just the "running" amperage.
Transistors are manufactured in NPN and PNP configurations. NPN is the most common type. You must replace the defective part with the same type or other steps must be taken to ensure that the resistors which bias the transistor are of the correct size and are placed to cause the transistor to forward bias properly.
Transistors have the ability to use a DC voltage to carry an AC signal. Most likely, the circuit board toes not generate an AC signal, but that cannot be ruled out until it is looked at by a qualified technician. Another component that is likely present on the circuit board is either a 555 or 556 solid state timer used to control the amount of time the transistor is switched on..
Unless you have the correct level of training to replace the transistor yourself, I would strongly suggest that you find a qualified technician. Transistors may be biased using several different techniques depending on the application. I suspect that the transistor in this particular application is "based biased". If you do not understand these terms as they are applied to transistors, do not attempt to make the repair yourself!
A discrete electronic tutorial is beyond the scope of this medium. Please do not ask for further explanations for any of the aforementioned terms. The summary above is a two year culmination of both analog and solid state electronics training including many mathematical formulas needed to properly bias transistors in single and multiple stage amplifiers.
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Steve Spence
AMSOIL - The "Once A Year" Oil Change
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My guess is the OP doesn't want to spend much - and a generic auto aerial can be bought off Ebay etc for not a lot. I'd say a repair shop would likely charge more than a new one. In the UK most electronics repair places - if you can find one - have a minimum charge of about 50 gbp.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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