well, i was having problems with my voltage dropping (according to battery gauge in instument panel) when driving with the lights on or accelerating at more than half throttle. i took off the alternator and took it to a shop to to get rebuilt. the guy there ran it on his machine and said it was fine. i then replaced the battery and the serp. belt, but it is still doing it. the voltage is fine without lights on or any sort of brisk acceleration. i guess i'll replace the alternator, but why wouldn't the testing machine indicate its not working properly?

 

little help

 

Most of those machines aren't really the best and can't see everything going on. Generally they only test at certain rpms and don't really get the whole picture, not to mention the whole load factor plays a big part. It could act fine during the day then crap out at night when you're stopped at a light with lights on, stereo blasting, and fans running full blast.
It appears that I have a bearing going out in mine- finally found the source of my stupid squeak noise- so don't feel bad...
In general I have found the majority of auto parts employees to be incompetent- all they have to do is hook the machine up and hit the button. I like to ask the older guys that have been around for awhile.
Might as well get it rebuilt and be happy it wasn't something major