Edwards 5520 Horn/Klaxon Repair

[sonnytiger]

I got this cool thing in a lot with a bunch of other stuff, and much to my disappointment nothing happened when I applied 24V DC to the power terminals.

I started checking a bunch of stuff, bypassing the plug and applying power to the circuit board, I checked resistors transistors and capacitors and the horn itself with everything coming back fine. The worst part is that it draws zero current and I can't find a fuse anywhere. I need help!

I will include some pictures.
https://imgur.com/gallery/zNmoO

I also have a video I will link to.
https://youtu.be/AJz-M5TY-50

[Gregg]

Those Edwards sirens sure are expensive; but they look well built.  From my experience with cheaper home alarm sirens; often the voice coil is the first to die.  From your pictures, it looks like an orange wire has been pinched rather hard.  That large blue cap looks a little dodgy like somebody added it.

[sonnytiger]

I checked that cap and it has the rated capacitance, no break in the orange wire, and the voice coil has a resistance of 6 ohms, a reasonable value.

Yeah I imagine it would have been a couple hundred new, it is really nicely made a big reason why I want it to live.

Thanks for the suggestions, need more!

[Armadillo]

Nice Cat in the video 

Power up the transformer and then measure "AC voltage" from the secondary side, best without any load [wires disconnected], then you effectively isolate one part of it from the troubleshooting equation.   

[sonnytiger]

Yes he likes to make am appearance in most videos.

The transformer is an output transformer for the speaker and it's windings measure a reasonable value.

[Cyberdragon]

Possibly a stupid question, but are you sure it's 24V? The 5520 is sold in several different models based on a letter code. What's the letter code on your unit? Since it didn't go bang, it's probably not the AS model (12V).

[sonnytiger]

It's the 24V AC/DC model. I wish it was a simple fix 

[Cyberdragon]

Well, if you checked all the components, the only thing left is a bad solder joint or a wire with a break in it.

[sonnytiger]

I tested all the wires and inspected all the solder joints, everything checks out. I suppose I should test all the resistors now? Running out of options

Edit: I believe I have found the problem, there is chunky resistor in series with the input that is measuring ~2.5  M ohm when it should be 1 ohm. Score.

[sonnytiger]

Yep that fixed it, 50 m of 18 awg sufficed as a 1 ohm resistor for testing. Thanks for all the suggestions guys.

Have a good one!