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Please help me fix strobe light alarm circuit

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spitso

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Hi all

I have a party this saturday and want to add a little bit of lighting effects. I decided to use one of those blue lights off the front of security alarm boxes. It worked fine to begin with (flashing the strobe maybe once every 3 seconds) running on 12v. But i stupidly turn voltage up to 30v which made it flash a little bit more rapidly but of course i heard a loud pop, and didnt work.

I opened it up and saw that a 100µf 12v capacitor had blown, i replaced this but still didnt work. Check all diodes for continuity all was fine a apart from one diode (which had a green band instead of a silver band?)which didnt conduct anymore so i also replaced that (dont know if it was right or not), but still not working. They only thing i can think of that is broken is the transitor but im having trouble working out what i could replace it with, all it says is d789, maybe you can tell what i can replace it with via circuit diagram.

Please help me fix my circuit. below are photos of the device as well as a circuit diagram i ROUGHLY put together.

thank-you
 

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Chippie

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A BD139 would do you or any NPN power transistor with a Vce of around 80-100v and a reasonble hfe...and can dissipate a couple of watts
 
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spitso

Member
no luck. begining to think that maybe it is the transistor thats bad. Ill take it to my tafe teacher tomorrow se what he think about it.
 

spitso

Member
teacher was no help.

I am now thinking that another fault is the transformer. Ive tested it with multimeter and their are no broken circuits, but when i apply 4.5vAc @ 0.5A on primary i only get like 0.5V....correct me if im wrong but isnt this transformer meant to step-up the voltage to about +300V AC? Below are pictures of the transformer, dont know what i can replace it with, but i do have a mini audio transformer 1K ohm Centre Tapped - 8 ohm Output Transformer - Jaycar Electronics

any ideas for next step?
 

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