Older Home Security System - blowing fuse

rjexit5January 8, 2014

I have an old Radio Shack brand security system wired within my home. We had a power surge at my home that blew out my garage door sensors and killed the alarm system. I fixed the garage doors sensors with replacement boards but the alarm system continues to blow one of the internal 1.5 amp fuses (fuse for the 3 control pads in the home). I am not sure where to start, any ideas/suggestions?

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Ron Natalie

Disconnect the control panels and see if the fuse still blows. Then connect each one individually...divide and conquer. You may have some component of the alarm that's still fried.

    Bookmark   January 8, 2014 at 1:44PM
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bus_driver

Often when surges ruin electronics, there will be visible damage to one or more of the components on the circuit board. Identifying and replacing those components is one way of MAYBE returning it to useful condition. Blowing fuses indicates that it may be the internal power supply of the alarm system.

    Bookmark   January 8, 2014 at 5:18PM
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westom

Electronics need AC voltages converted to DC voltages. That conversion provides other features including current limiting. Even a DC short circuit (shorting all DC wires together) would not blow that fuse. Blown fuse means something between that fuse and the 'AC to DC' converter (also called a power supply) is defective or shorted.

Electronic failures rarely have a visual indication (other than the blown fuse).

More important is a reason for damage. Your damage is typical of a house that ddid not properly earth a 'whole house' protector.

    Bookmark   January 9, 2014 at 10:21PM
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Ron Natalie

Eh? I'm not sure what the power supply has to to with it.

The fuses he's talking about are almost certainly on the DC side of the circuit. The power to the control panel is 1.5A at 12V. It's quite possible that a failed panel would blow that fuse.

    Bookmark   January 10, 2014 at 7:41AM
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westom

> The fuses he's talking about are almost certainly on the
> DC side of the circuit.

Please learn how power supplies work. A previous post said what you should have known:
"That conversion provides other features including current limiting."
Short all DC outputs together and any properly designed supply goes into current foldback limiting - no fuse and no hardware damage.

Fuse would be on the AC side. A fault would be somewhere between that fuse and an AC to DC converter - the power supply.

Please learn basic concepts found in all power supplies; even early 1970 single chip supplies (a whole power supply inside one IC). The technology is that old and that standard. Obviously, no fuse and no reason to have a fuse on the DC side.

    Bookmark   January 10, 2014 at 1:22PM
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Ron Natalie

I read it and it makes no sense with regard to the way alarm systems are built. These fuses are on the DC side. The poster said so, and they have to be. The thing is fed by an EXTERNAL AC 12 V @~3A. The DC is generated by nothing more elaborate than a diode and a couple of caps.

    Bookmark   January 10, 2014 at 7:32PM
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bus_driver

"Electronic failures rarely have a visual indication (other than the blown fuse)."

Westom's statement does not match my experience. A careful inspection with a magnifier has ultimately resulted in the repair and salvage of many circuit boards-- especially when no service information was available. And "looking" costs very little.

    Bookmark   January 10, 2014 at 8:01PM
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rjexit5

Turns out that I gave some bad information; the fuse that is blowing is the one for all senors and alarms (not the one for the 3 control pads). This seems rather hopeless given there are 14 window sensors, 8 room motion defectors, 3 alarm bells, and a few smoke detectors. I am betting one of them is fried, now I just have to find it.

    Bookmark   January 13, 2014 at 8:07AM
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Ron Natalie

Disconnect everything from the alarm box (except for power) and see if it still blows. If not, then just connect things back one at a time. You'll probably want to lay in a few spare fuses, but it shouldn't take long.

    Bookmark   January 13, 2014 at 9:16AM
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