Most problems with a keyboard can be solved with a soldering iron. The most common cause for only a few keystrokes not registering is some dodgy solder joints. To fix this all you need to do is reheat the solder until it’s molten again and allow it t suck itself into the PCB. Apply more solder at this time as well if it’s needed but you won’t always need to. After re-flowing plug in your keyboard and try the switches again. If you still have no luck then you may need to re-flow the diodes of the switches, the method for this is the same, simply melt the solder and allow it to flow again before removing the iron and letting it cool If you opt to re-flow diodes please refer to another guide though as I will not be going into detail on this process.
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