Festool DTS 400 EQ repair


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3 May 2022
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East Sussex
I have just bought a broken Festool DTS 400 EQ with the intention of trying to fix it. It cost me £40 so its not the end of the world if it never works again.

The symptoms it has are 'smells a bit and starts smoking in use...'. I had the same symptoms on my rotex before I sent it off to festool and they replaced the armature on it. I'm anticipating this is an armature problem, any advice on testing before I go ahead and order a replacement armature.

I've been reading this which seems to make sense https://www.groschopp.com/how-to-check-a-motor-armature/

Have a look at some of the most recent videos on the Squatch253 youtube channel. He has just rebuilt the starter motor and dynamo from an old tractor. He goes into good detail on how to check the armature. Do you have a growler and hacksaw blade?
Don't have a growler, I did watch a couple videos with them and they look cool, probably a bit pointless for me who is only likely to test an armature once every 5 years or so...

I'll have a look at the youtube channel you suggest
Was hoping to try and confirm it actually is the armature before buying the replacement as it’s twice the price I paid for the tool itself (granted not a huge amount but would be a waste)
How much do Festool charge for the repair?
If it isn’t too much, £40 plus the repair fee may still yield a cheap fully functional tool.
The best way to test an armature is with a growler, with smaller motors it is just as easy to replace the armature or omplete motor.
So the thing is apart, have done three tests on the armature:
- Opposite bar resistance
- Bar to bar resistance
- Bar to commutator continuity.

Nothing exciting has appeared.

If I knew where I could go locally to find someone with a growler then I would, what sort of place would I be looking for to try?

The original problem was that when turned on the motor would not spin, and it would begin to make an offensive noise.

I continued taking the thing apart today and found an extremely stiff bearing which handles the offset weight that the motor drives to give the vibrations.

Re-assembled the whole thing without the bottom half, so the motor is not actually driving anything now. Turned it on and the motor works fine! Thankfully I didn't go ahead and buy a replacement armature on the whim, and it explains why the test results in my previous post give no indications of a problem. Clearly something the motor is driving is causing the issue, and this bearing is the prime suspect!

I pressed out the brass offset weight from the inner race, and then pressed the bearing out of its aluminum housing. It is a 6001 2RS bearing, I've ordered a new SKF one for £4.16 which should come this week.

Total spent so far is £44.16 (£40 for the broken sander, £4.16 for the bearing)
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If I knew where I could go locally to find someone with a growler then I would, what sort of place would I be looking for to try?
Any motor repair / rewinding workshop, fewer around these days because imported motors are cheap and it is not economical to rewind so it is the larger industrial motors that get rewound. It would take only minutes for someone to check your armature on a growler and then you would know it's condition.