Replies

1. 
   JohnWW | Aug 27, 2003 11:42pm | #1

   Matthew,

   I've seen this reported elsewhere and it's supposed to be a sign of worn out brushes.  Apparently when the brushes wear past a certain point the electronic brake no longer functions, but I've never seen an explanation of the reason for this happening. 

   Brush replacement on most saws is very simple, your owner's manual should cover it.  If you do replace the brushes, I'd like to know if that solves the problem.

   John W.

1. 
   Steinmetz | Aug 28, 2003 12:07am | #2

   John, I suspect a burnt out solenoid coil connected to the brakeshoes.

   In order to stop swiftly, some power tools employ a pulse or DC current to 'Stall' the motor.

   Others, utilize a solenoid brake that pulls in as soon as the swith shut off the motor's power.

   Stein.

1. 
   JohnWW | Aug 28, 2003 12:55am | #3

   You got me interested so I went online and found a Bosch service manual, though I'm not sure it is for the model saw under discussion.  According to the manual, I'm probably right, the saw has an electronic brake and they list worn or sticking brushes as a reason for it not to work.  On other tools, especially larger machines your solution would have been just as likely the fix.

   John W.

   Edited 8/28/2003 8:52:55 AM ET by JohnW

2. 
   MatthewSchenker | Aug 28, 2003 05:22pm | #4

   I took the brushes out, and I believe they are still OK. There is a line showing how badly worn out they are, and mine seem to still have a way to go. But I decided to change them anyway. Well, two hardware stores I went to don't have the correct size. Oh brother, why does everything have to become a major project.

   Today, I'll check a couple of other places and try to find them.

   I'll report back to the forum when (and if) I replace the brushes, and let you know if this solved the problem.

   Edited 8/28/2003 10:23:38 AM ET by Matthew Schenker

1. 
   JohnWW | Aug 28, 2003 06:51pm | #5

   Probably the only way to get the brushes you need is through Bosch directly or through one of their repair centers.  Despite their simple appearance, modern brushes are fairly sophisticated, it would be far safer to use factory parts in this case.  Bosch has a web site, http://www.boschtools.com that will help you locate a repair center, but it is mute on how to order parts directly.

   Since the brushes look good, try to very lightly sand or file them on the sides to allow them to slide a bit more freely in their holders, it might just solve the problem.  Be sure to remove the carbon dust before you reinstall the brushes. 

   Take a close look at the brushes, are the springs in good shape, still flexible and not soft or burned looking?  Also if the brushes have wire pigtails, are the wires solidly attached to both the carbons and the copper terminals at the ends of the wire?  Sometimes the wires will look good but pull right out or break with a gentle tug.  Soft springs or bad wires could explain why the brushes can look good but not function properly. 

   While the brushes are out, take a flashlight and look down into the brush holder openings, the sides of the tubes and the commutator surface should be smooth and shiny.  The commutator may be dark colored and have some small ridges in it, but it shouldn't be pitted or burned looking.  On some machines the inside of the brush cap can have a copper or brass disk installed to carry the current to the brushes, make sure the disk is in place and not burned up.

   Good Luck, John W.

1. 
   MatthewSchenker | Aug 28, 2003 10:31pm | #6

   John,

   Thanks for your very informative reply. It looks like the carbon brushes are really the culprit here.

   I wrote to Bosch customer service about the problem. Today, I received a response back from Bosch about my problems with the brake. Here is what they wrote:

   Dear Matthew,

   Thanks for writing!

   A common problem causing late brake activation is carbon build up on the commutator bars of the armature. Remove either one of the brush caps and brush(unplug the saw first). With a standard pencil, insert the "erasure" end down into the brush holder until the erasure contacts the comm bars. Then by hand, rotate the blade while holding the pencil erasure against the comm bars until the black color of the com bars begins to turn back to its normal copper color.

   This procedure with remove the carbon build up providing better contact between the brushes and comm bars and also return the brake function back to normal.

   John

   Bosch Customer Service

1. 
   JohnWW | Aug 28, 2003 11:27pm | #8

   Interesting, I hadn't run into this fix before, I'd like to know if it works.

   Thanks, John W.

2. 
   MatthewSchenker | Aug 29, 2003 08:09pm | #10

   Well, I did as the Bosch representative said, and it improved one thing while making another thing worse. After using the pencil eraser to clean the commutators, the motor cuts off right away, but the blade keeps spinning freely for 5 or 6 seconds. Essentially, the blade comes to a halt naturally now -- there is no brake function at all.

   I have written again to the Bosch rep to see what else can be done. I think I might need brand-new brushes at this point. We'll see.

2. 
   IMERC | Aug 29, 2003 06:19am | #9

   If you are going to sand motor bushes use a virgin household cheapo sponge (dry) wipe in one direction only and not very much at that, as in only a few swipes to a side. Clean the brush holder with a Q tip and denatured alcohol.

   Soap stone the commentators and clean the seperrations with a tooth pick. Wood or plastic. 

   Leave out compressed air during all of this. 

   Who ever invented work didn't know how to fish....

2. 
   Jimma | Aug 28, 2003 10:45pm | #7

   Matthew -- This is off topic, but didn't I promise you a while back that I would let you know when I posted a picture of a showcase joint? In any case, it's in the archives under message number 13247. Jim