Repair SMD in amp

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To remove the old resistors...

Apply new solder to both ends. Heat one end for ~2-3 seconds and then 'quickly' move the iron to the other side. If your iron is hot enough, the resistor will immediately slide off of the pads when the solder melts on the second pad.



To replace the resistor...

Remove the old solder from both pads with desoldering braid. Apply solder to one pad. Hold the new resistor with tweezers, hemostats or whatever you have handy. Heat the pad with the solder on it and slide the resistor into the molten solder. Reposition if necessary and then solder the other pad.
 
Soldering SMD resistors and capacitors down to 0805 size (and other two or three lead devices) is quite easy if you can get the right type of tweezers and a soldering iron with a fine tip.

SMDTWEEZ.jpg


To unsolder components: Heat both ends alternatively and quickly until it comes loose.

To solder components: Hold the component in place with tweezers and solder one end. Then press with the tweezers on the center of the component to keep it in place while you heat both ends alternatively to make it seat properly on the PCB. There is no need for removing the solder that way.

SMDTWEE2.jpg
 
In car amps, the resistors that fail often produce significant heat and the solder is badly oxidized. Using solder that's badly oxidized will produce a poor solder connection. If the resistor failed quickly and the solder is is not oxidized, you should use additional flux to float contaminants to the surface where they can't cause any problems.
 
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