Wired doorbell doesn't work?

have a wired doorbell that stopped working after four years. purchased a new transformer, bell and chimes. installed all exactly that way the previous one was installed. still does not work. in fact, new transformer gets pretty hot; but, in testing the bell wire terminals on the front of the transformer with a low voltage tester, it does not show any juice. we have tried a transformer, originally, alone, and that got extremely hot, to where you could smell burning and that's what made us purchase everything new, including a second new transformer. we think that's where the problem is starting from, the transformer. does anyone have any ideas why this is happening and how to correct the problem? thanks for your help.