[quote]Must capacitors go in a certain direction like plus or minus? Can they be checked while still installed on the board or must they be removed first[/quote?]
Yes, capacitors MUST be installed according to polarity. In 99% of instances, the polarity is marked on the PC board.. with a half-moon shape painted to represent the negative polarity. There also may be the + and - markings. Capacitors are polarity-sensitive, causing a shorting effect if installed wrong. Some capacitors are not as polarity-sensitive, such as the "dry" or "ceramic" type.. but still should be installed with polarity in mind.
And yes, the old item must first be removed without damaging the circuit traces or PC board. Then an exact replacement installed.. or you will alter the design of the circuit. Use of a soldering gun or iron of about 80 watts or higher to work the solder joint is important. You want to "get in and get out" with the heat quickly so as to not cause damage to traces or nearby components. Use of soldering wick can help remove the solder dross.
Checking capacitors in-circuit is not advised, unless you have a special piece of test gear.. expensive! Capacitor Tester
Capacitors are designed for circuit use specifically. The majority of applications are intended to smooth the AC ripple and surges in power circuits, providing pure DC power. The secondary use of capacitors is as a coupling link between circuits having different voltages, to keep DC levels unchanged yet allow AC signals to pass as needed.
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