I purchased my HP 6730B business laptop used. It was in a very nice condition, had Windows 7 Professional and ran great until the charging unit started beeping. I could shake it at first and tap on it and it would stop beeping and work again. This got more frequent within days.
Then the tapping and the shaking stopped working, so U placed it in the freezer for 20 minutes. This also worked for another week or so. Then the beeping became louder and neither the freezer trick nor the tapping worked. So I blasted it with a hammer a few quick times and it squeeled like a stuck pig and the beeping got louder and is now steady (whereas before it was intermittent).
In any case, I got one from a friend that is lower in volts by .5. It's 18.5, not 19. Also it has less amps (3.5, not 4.7). The wattage is different: 65 watts, not 90 watts.
There hasn't been a noticeable difference, except that when the old charger had completely charged the battery the icon would read "battery fully charged", "plugged in, not charging" — now it only does this sometimes and I noticed my cooling fan is on more often, although it has gotten considerably warmer where I live, so I'm thinking this is a temporary fix.
I'm going with the original manufacturer specified unit ASAP, and although lower watts/amps/voltage works, original gear is always better.