Here is how I did it:
Since my Alero only had 27,500 miles on it when the alternator went, and I could assume that the bearings were OK (spun good), and because I've always wanted to do it, I decied to try to repair it. Not do a rebuild, but simply remove and replace just the bad part. First thing I did was to take the known bad alternator to an auto parts store, just to see what it does on their testng machine. It tested bad, and I watched them to see what the meter showed. Then remove the alternator and remove the back plastic cover. Then I removed the voltage regulator and the rectifier. It looked like this:
I then checked the resistance between the input of the brushes and ground and got about 4.5 ohms. You check between where the red pointer is and the case:
That told me that the brushes and rotor were good.
Then I checked the resistance on the three stator leads. Check them all to each other and between each of them and ground. I got infinite resistance to ground and almost no resistance between any of the three places where the red pointer is:
That told me that the stator windings were probably good. That left only really two possible places where a problem could be, the rectifier and voltage regulator. To test the rectifier, you first remove it (you will need a good soldering gun to melt the high temperature solder that the auto parts makers use). I destroyed the diode output leads when removed mine. I also removed the plastic cover on it for this pic. To test it used the diode check function on my multimeter and the 3 inputs to the diode pack, places shown in red here:
When I did this check I got nothing, as in all my diodes were an open circuit. So I ordered a new rectifier off of eBay for a CS130D alternator, and got it for $26 shipped. It looked different than the original, but fit just fine and when I ran the same check I had run on the one I pulled above, I got different results that indicated that it had working diodes in it:
So I soldered the new rectifier in along with the existing voltage regulator. Note that there are also 4 screws holding it in. One of them is shorter and has a insulator in it. That one goes here:
You need to remember this since if you use a longer screw it will go completely through the case and hit a fan on the inside. If you forget to use the insulator on the short screw, it will also hit the fan on the inside as well (and fail any initial spin test) as well as short out the battery connection to ground (also very important). Then I took it to auto parts store for testing and watched it again and the output was much better this time (voltage output was in the good range). So it looks like a success, but I won't know for sure until I install it and drive with it for a while. It still could have failed the auto parts store test if it had a bad regulator, but that part is easy to replace and only has two screws and one solder joint holding it on so I figured I could do that later if it failed. Also, statistically speaking they don't go bad all that often and aren't under a lot of stress, etc.
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