Better divide the sentence before understanding it.
他喜欢拆电脑等等,各种机器上的零件他都想拆下来看看。
Literal translation: He likes taking apart computers and so on; he want to take apart and check all kinds of parts in machines.
In this sentence, 零件 means "parts", 拆下来 means "take apart". “下来” alone can have various meanings which vary to their combinations.
Hope that helps.