Festool sander RS 400 EQ problems, performance drop

[oakheart]

Dear festool-owners,

i own a Festool sander, model RS400EQ which doesn´t work properly anymore.

As my mother tongue is German please excuse my wording  [wink]

During sanding with the machine it suddenly lost performance. It dropped to 10% approximately.
Now it only starts in highest mode, but only at a fraction of the initial power. Not starting at all at the lower modes; just an electric buzz noise to hear. (see videos below)

The bearings work smoothly as i can tell, the anchor (?) turns without any issues.
I disassembled the whole machine, cleaned it (wasn´t that dirty at all, just a bit of fine wooden dust),
replaced the coal brushes; but still not working...

Getting pretty warm when plugged in; but no smouldered spots noticable. Everything looks quite fine at the inner side.

The thing surrounding the anchor (inductor stampings? don´t know the english word, sorry) I measured the resistance, which is about 26 ohms. Does have continuity.
I´m not sure about the measurement of the anchor.

I uploaded two videos of the problem at youtube:
Video 1 - dropped power

Video 2 - lower mode - doesn´t start - buzz noise

I would be more than glad if anyone had an idea how to fix it.

many thanks in advance,
Markus

 

[rvieceli]

[member=5277]Alex[/member] any help here. You're the resident repair expert  [smile]

Ron

 

[AlexThePalex]

Yes, I know this problem, have seen this myself with 2 sanders I bought as defective. And it is defective, the field coil is burned and needs to be replaced.

The sander appears to be working at 10% because it is not turning around like it should, it is buzzing in place, a rocking motion. You get the idea it works because of the sound it makes, but there is no useful motion anymore. That also explains why the sander gets hot, it is because the cooling fan does not turn anymore.

Repairing it is expensive, I'd suggest you trash the sander and get a new one.

Do not buy a new field coil on my behalf, I'm just making a suggestion over the net but you can never be sure until you've seen the tool in person. Get in touch with Festool's repair department if you still want to have it repaired.

But considering it is an RS and really old, I'd get me a new sander. I buy most of my Festools used, I could get an RTS 400 for like 100-125 euros.

 

[oakheart]

Yes, I know this problem, have seen this myself with 2 sanders I bought as defective. And it is defective, the field coil is burned and needs to be replaced.

The sander appears to be working at 10% because it is not turning around like it should, it is buzzing in place, a rocking motion. You get the idea it works because of the sound it makes, but there is no useful motion anymore. That also explains why the sander gets hot, it is because the cooling fan does not turn anymore.

Repairing it is expensive, I'd suggest you trash the sander and get a new one.

Do not buy a new field coil on my behalf, I'm just making a suggestion over the net but you can never be sure until you've seen the tool in person. Get in touch with Festool's repair department if you still want to have it repaired.

But considering it is an RS and really old, I'd get me a new sander. I buy most of my Festools used, I could get an RTS 400 for like 100-125 euros.

Dear Alex,
thank you very much for your assessment.

I found 2 videos of how to test the field coil and the anchor.
field coil testing
anchor testing

Do you think this testing method tells me trustworthy if the part is broken?
Following the video for the field coil, the 2 resistances are the same, about 26 ohms and there is continuity between the inlet and outlet cable...

Replacing only 1 part by myself (so just anchor or just field coil) is about 40-50€. Would that damage the new part, if I changed the wrong part? I mean if I believe the field coil is broken; so I change it; but i reality the anchor is the defective part; could it break the new field coil (ans vice versa if i bought only a new anchor)?
Replacing both would be 90€.
I would like to test it so i can tell by 99% which is the defective part so that I don´t have to buy both.

Otherwise you´re completely right; I could get a RTS 400 instead of spending 90€...
100-125€ sound awesome, but not to find at that prices here in Germany (ebay etc). Do you have reliable sources for that sander? I see you´re from the netherlands, maybe I could ask you about that via personal message.

Any other suggestions are much appreciated.  [smile]

 

[AlexThePalex]

I don't know about those tests, haven't done them. If you're willing to replace both parts you're probably fine. I don't know if a new part could be damaged by another bad part, I am not sure but I don't think it will.

Remains the fact the RS is very old and another part can fail next day. I have a DS400 from 2006, still doing fine, but I can feel its age, especially when I compare it to the DTS400 I also own.

I find my tools on the dutch website www.marktplaats.nl.
https://www.marktplaats.nl/z.html?query=rts+400&categoryId=0&postcode=1941BE&distance=0

There are a few RTS 400 right now, cheapest is this one:https://www.marktplaats.nl/a/doe-he...285449651fa109c354bbabe740c1b&previousPage=lr

Though it is cautioned on marktplaats to sellers to do business with people from a foreign country, especially when they are new. There are many tricksters unfortunately and on marktplaats you don't have the protection you have on eBay. So it depends from person to person if they are willing to ship cross borders.

You also need to look out as a buyer, once again, many tricksters. Seniority is a good indication of trustworthyness. Bad sellers are weeded out quickly. In the case of above seller with 13,5 years of being a member you're probably good.

 

[ragp13]

Reviving this thread because I have a similar/identical issue with my DTS400EQ.

The motor started dropping down to ±10% speed while sanding and hasn't recovered since.

Things I have done:
- Bypassed the speed dial: No real effect. Except that setting the dial at lower values sometimes leads to a stop of the motor. And I noticed turning it above a certain value doesn't really increase speed anymore.
- Cleaned the inside with air compressor
- Motor/armature/anchor can turn with relatively little resistance. So bearings seem OK
- Measured motor with the two videos above as a guide and found nothing odd
- Cleaned brushes (they are still big enough)
- The brass flywheel (whatever it's called) could also spin freely
- Fans can spin freely

I still suspect this is a rotor/motor issue. But any tips for troubleshooting would be appreciated.