Resoldering the battery holder leads on a Cobra Beach Magnet

[waterfalljay]

Ok, so the battery housing on my Cobra Beach Magnet vibrated loose while on a long road trip. The battery holder fell out, severing the leads to the unit. I believe I can resolder them, but I can't figure out which of the two contacts in the housing is positive and which is negative. The wires are the usual red positive and black negative, but the solder spots (terminals) in the housing are not marked. Anyone know which is which? As low end as this machine is, I'd hate to toast it by accidently hooking up the polarity backwards. Thanks!

 

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[Rusted Nail]

Easy way to check is put batterys in it and use a volt/ohm meter , most of the newer ones have a digital meter and show if test terminals are placed correctly.

 

[Frankn]

Most detectore have a built in blocking diode to protect them so if you put the batteries in backward no harm is done. Just touch the wires to the terminals. If it works, that's where they go. If it doesn't work, switch the wires. It's that simple.

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[waterfalljay]

Thanks for the suggestions folks. Even Kellyco won't work on a Cobra (despite it being their in-house brand machine). They offered to replace it for $200. I opted to "fix" it by buying a used Tesoro Sand Shark.

 

[WishfulThinker]

Not guaranteed but worthwhile starters:
Find both solder pads for the battery holder -- look for broken wires.
USUALLY the connection path going to the on-off switch is the Positive Lead (Red).
The Black Lead will USUALLY go to a connection point that is ground bus for the circuit and will connect/trail-through to a BUNCH of Transistors, Capacitors and Resistors. Cheaper Metal detectors may use alternate designs and really FUNKY configurations, but assume the best case. If you really want to get technical -- look for IC power connections and get transistor numbers and check wiring pattern.
One real easy area to follow through on is the audio output/speaker driver circuit. Will probably use standard transistors or Integrated Circuit Audio Driver Amp. Power connections to IC or transistor will be obvious, to someone with electronics experience.

Be careful with TWO BATTERY configurations (two 9-Volt batteries), as the batteries are supplying positive and negative difference voltages to front end ICs or amplifier circuitry. Otherwise (single supply voltage, 12-Volt), special voltage divider circuitry is used to achieve same effects.

Carl has some schematics on Geotec1 website, very helpful, for beginner or someone assisting you.