Bosch 4000 Table saw

[ifix2ls]

Hey guys,
New here. Been buying parts but never used the Forum, so here goes,
Customer called and said that his Bosch 4000 started tripping his breakers in the shop and the motor is struggling also running backwards?
I took the motor apart to find the armiture is good along with the brushes and the bearings. The windings look a little discolored but not fried. So why is the motor running backwards all of a sudden? I checked the switch then plugged the motor direct into the current(20amp)
by-passing the switch and also reversed the wiring on the cord, same thing....it never tripped my breaker but it does run slow and backwards. What do I try next?
Thanx for your help!
Mike

[cmoorejack]

Hey Mike,
Not a quick fix on this one..The polarity has reversed itself..If the armature checks out ok with a growler test..I would suspect the speed control and the field are bad or shorted..I would replace both just to be safe and that should take care of it..[I haven't come across this problem before ,but you only have 3 components..armature ,field,speed control..the switch and cord just provide power to the tool..you can do an ohm test between the field coil windings to see if they match up close..but if you have discoloration there is probably some heat damage and the windings have shorted to each other..
Hope this helps?
Craig

[ifix2ls]

Thanx Craig,
Ill give that a try.
mike

[Dale]

The field is the weak link on this tool. Hope your armature is ok.

[ifix2ls]

Ill look at that also Dale
Thanx,
mike

[bummer]

I bought a bosch 4000 about a year and a half ago. I used it for one light job and let it sit for about a week. I tried to used it again to finish the job, but it bogged down and ran in reverse. I am very upset. It's brand new. I have used many bosch table saws at work (treating them much rougher than this one at times) and have never had this problem. I am convinced it is a factory defect. Any one else heard of this problem.

Also, if it is known what is wrong now, can I please get a little help.

Thank you

[Dale]

Yup it's your field. should still be under warranty. Hope this helps. IF you need me to I can find your closest service center.

[MarkB]

Wow, what a telling thread. I guess I'm not alone with my Bosch 4000 saw problem.

My Bosch 4000 hasn't run backwards but here's my sequence of events:

Normal operation for about a year or so (light homeowner use, no abuse/overload, ever).

Then one day:

Saw running, no load (getting ready to cut some moulding).

Suddenly speeds up like 2X. Immediately shut it off.

Tested it a few times to see what was up. Goes immediately from a dead stop to overspeed, and has an "electronic" smell.

Figured the speed control went TU. Ordered another one and replaced it.

Overspeed condition now cured, but it doesn't sound the same. Draws more current than normal (flourescent lights on the same circuit flicker, cord gets warm).

Serious arcs around the commutator when it runs, nearly a continuous blue flame around it's circumference.

Took the motor apart. All looks fine- no zorch marks, signs of burning, bubbling or any issues that would indicate a failure or overload.

Brushes showing signs related to the arcing but are otherwise in good shape. Brush holders and springs seem fine.

Had it tested at a commercial motor repair shop. Armature tested both on a growler and a 3 phase tester for impedance anomalies on all windings. No trouble found. Was told the
field tested "OK" but after reading this thread I'm beginning to wonder.

Since we are only talking about 3 active components here worth over half the value of the saw, and one of those being new (speed control) I'd hate to just shotgun it with a new
field and armature.

Is there a better test to perform, even if I have to mail it somewhere to do so? Or any opinion of what it might be or should try first?

Figured I'd buy a nice saw and have it for years. Now I'm faced with a repair cost that exceeds what I can get an entire cheap chinese saw for...


Mark B.
Albuquerque, NM

[Dale]

If your Armature test's good. I would spend the money on the Field. $ 57.00 its worth that. if you don't mind twisting a wrench. 90% of the time its the field.

http://www.ereplacementparts.com/bos...8_167_168.html

[MarkB]

Followup:

Based on the info in this thread I took a chance and ordered a new field and installed it last weekend. The saw now works like a charm. I let it run for a while to break in the brushes a bit and make sure nothing overheated, and it all seemed fine. Other than crossing my fingers every time I turned it on, it performed perfectly all weekend cutting hundreds of linear feet of 1" plank.

Out of curiosity I unwound the old field to see if I could find anything obvious wrong with it and couldn't. No copper snot, zorch marks or signs of overheating or abrasion anywhere that I could see. That's not to say it couldn't have been shorted at some tiny spot that I missed (~150 feet of #18), but it's not like it suffered some major and obvious trauma or abuse.

So thanks guys, and hopefully this will help the next guy with a Bosch saw that mysteriously fails without warning.

Mark B.
Albuquerque, NM

[JMHawaii]

I realize this is a couple years after the last post but wanted to comment because this thread saved me money and time. Namely the Mark B entries. My problem was nearly identical with a sudden high speed action occurring while in the middle of use. I also had the crazy arcing at the brushes. At onset of issue I immediately turned off and went through the obvious checks. I was wondering how much to invest or whether it'd even be worth fixing. I decided to check if anyone else had similar experiences and went off of this thread. So I changed speed control, field, and brushes. So far so good. Thank you all for the great information.