NO DIY repair for you (festool rotex)

[kripton2035]

Hi Folks,


I was sanding some old table to make it live again, and my "trusty" festool rotex orbital sander suddenly loosed power
the motor still turns on, but the dimmer seems at the lowest speed, and there is almost no torque.


I have this sander since 2007, and it is out of warranty for sure so let's open it, it must be a simple dimmer circuit right ?


alas, festool said: no repair for you DIY apprentice... everything is sunk in a blue resin...
must be some capacitor dead, so a $1 component.


still the full module is available for ... 112 euros plus shipping !


what a waste ...

[ataradov]

I doubt it is out of malice. This is just a heavy conformal coating. You can see all the wood dust. This dust absorbs water and becomes conductive. Without this, it would not have lasted since 2007.

[themadhippy]

Nothing to loose so try attacking it with some chemicals ,ipa as a starter ,if that dont work maybe acetone.

[Microcheap]

Does it have a brushed or brusheless motor?

The symptoms you described sounds like worn carbon brushes.

I'm not sure if it's the same model as yours, but I found this: https://www.festoolownersgroup.com/festool-how-to/changing-the-brushes-on-a-festool-rotex-150-sander

[KE5FX]

I don't think IPA is going to do anything to conformal coating.

If you really want to save it, there are a lot of things you can try without messing with the coating.  I'd pull up those aluminum electrolytics with a pair of pliers and solder new ones onto what's left of the leads.  Also take a look at the pot wiper and track.

And yeah, brushes would be an obvious thing to check as well.

[Kleinstein]

Festool tools usually use brushed that turn all the way off when they are worn.  So one would not get poor a fully off, not sparking and damaging the motor.

One may be lucky and it is only the pot in the electronics. There is a chance to get it working again by holing it with the PCB side up an more the pot several time to make dust settle away from the actual pot. Still only a slim chance.  Before ordering a replacement it would be good to give to motor (especially the collector part) a good visual inspection of there is damage. It would not be the first time that a damaged motor takes out the electronics or EMI capacitors.

Another point to check are the bearings - usually they are among the first parts (maybe to gether with the brushes and cable) to fail on sanders.

[kripton2035]

so thanks I will check the brushes it could be only that... not so sure seeing how fast this happened but it's worth looking.
when the sander is on, I smell a strange smell that is not like a burning capacitor...

[wraper]

The first thing I'd check is if Rifa 4n7 cap is not cracked. As of coating, you probably can soften it by heating with hot air or just dig into it with soldering iron.

[kripton2035]

well the brushes measure 11.7mm, and new they come as 12.5mm, and it seems thay can go as low as 6mm
so it should not be a brushes problem ?

I also thought of the rifa capacitor, but looking closer it does not seems to be cracked.

[Kleinstein]

The length of the brushes looks OK. I don't know the type but due to the turn off mechanism they may not work all the way down to 6 mm.  In some cases the brushes may get stuck from dust build up, especially when used with dry wall or similar more mineral materials.
Cleaning (but put them back the same way as the were) can sometimes help.

Which rotex type exactly is this ? There were different models over the years.

[kripton2035]

it's a 125mm FEQ rotex from 2007. I used the sander on wood mainly, and never on drywall as far as I can remember. also almost always connected to a festool vacuum.

[Kleinstein]

I forgot about one more common point of failure in these machines: the quick change cable. This is nice for a saw, but with the vibrations of an orbital or excenter sander they tend to fail quite often. So definitely check the contacts / connector. A bad connector is kind of contageous - the other side also tends to get bad over time if used with other machines.

[kripton2035]

you mean the connector inside the sander ? or the connector in the mains cable ? because the cable is bound to the vacuum and I use it with no problem on other devices.

[tszaboo]

I doubt it is out of malice. This is just a heavy conformal coating. You can see all the wood dust. This dust absorbs water and becomes conductive. Without this, it would not have lasted since 2007.

Looks more like potting compound. It's not very good for repairs, but it makes the electronics much more sturdier and reliable. Sometime you cannot even pass certifications without it.
I hate it every time I need to use it.

[Kleinstein]

you mean the connector inside the sander ? or the connector in the mains cable ? because the cable is bound to the vacuum and I use it with no problem on other devices.

A weak point is the connector for the mains cable (exchangable) at the machine. With the vibration the contacts loose force and start sparking sometimes and than oxidize.
If the connector is bad I would opt. for a conversion kit to change to a normal fixed cable instead of the PlugIt system.

The electronic is more liek potted with a half close case on the bottom. The sander seems to use true speed regulation with feedback from a magnet. So one can not simply bypass the electronics - without the motor is not made to withstand the full mains voltage at low load.

[kripton2035]

what does a burning rifa capacitor smell
is it the same classic burned electronic odour ?
I smell something different than the classic dead semiconductor or capacitor
when the sander is on.
do I need to replace this with also a rifa or can I use any 4n7 250v capacitor ?
thanks.

[Kleinstein]

If one really wants to replace the small cap, depending on the use one may need a class Y (often Y2 is OK) rated capacitor.
The small 4.7 nF rifa cap is very likely a class Y capacitor and these are very unlikely to fail - that is the main point of class Y. The class y caps are usually for EMI suppression (mains to motor iron), so it usually won't effect the machine runing but more the radios near by. If they fail it should be open and likely with no smell. Because they are usually very reliable I don't know how they would smell. While I have seen some 100 failed class X caps, I only remember 1 bad class Y - and that was a broken terminal wire. There may be additional unnoticed bad ones.

There are rare cases where RC nubbers also use class Y cap (because they are available, though not needed in that grade) effect the triac switching.

One may be able to temporary bridge the electronics and then run the machine with a low voltage DC (e.g. some 30-40 V - may take some 1-2 A). With this the machine should run at a reduced speed - a bad motor may show up as an uneven run.

[kripton2035]

rifa capacitors are known to fail by cracking after a few (10s) years.

the symptoms are: no regulation. the speed seems always at the lowest value, even if I move the potentiometer.
and a very subtle burn odour, that doesn't smell like I know (for dead mosfets, or dead exploded capacitors).
for me the rifa capacitor is here for the snubber, so if it fails it shouldn't reduce the speed like that ?
when a triac fails, it's often shorted, so the speed would be always max

what is the best bet for component culprit with these symtoms ?

[Kleinstein]

Getting a steady low speed is unusual, as the means the electronic is kind of working. The electronics seems to be true regulation with speed feedback from a magnet ring.
If there is a link from the electronics to the iron part of the startor (e.g. the connector close to the cap), than there should be a class Y cap. In this case the 4.7 nF cap would be used for this use and not as a snubber.

A little burn odour (NOx from sparks) is possible from the carbon brushes even in normal operation.

A possible isssue could a problem with the feedback and not signal may give a min speed to start getting a signal. AFAIK the blue THT inductor is used as a detecting coil. A loose or maybe shifted magent rind could be possible.
Another possibly issue could be the pot - so not getting the setpoint signal. I have seen failed pots with older Festo(ol) sanders after heavy use. It may help to try also intermediate speed settings, not just the maximum speed.

[kripton2035]

the speed is low at any potentiometer position.
the connector close to the cap is connected to the mains. the other mains is at the top left of the picture.
the black rectangular component just below is the on-off switch
the motor is connected to the two yellow wires

[wraper]

The small 4.7 nF rifa cap is very likely a class Y capacitor and these are very unlikely to fail - that is the main point of class Y.

That garbage fails the same way as their X caps for the same series.

[BradC]

The small 4.7 nF rifa cap is very likely a class Y capacitor and these are very unlikely to fail - that is the main point of class Y.

That garbage fails the same way as their X caps for the same series.

Yup :
https://www.eevblog.com/forum/repair/bloody-rifa-caps-again/msg5022112/#msg5022112

[kripton2035]

so, to finally close this topic ...
I ordered a replacement board from festool, for some 140€ with shipping... and it was not the culprit !!!!!!
the small jst connector at the top of the board goes to a ntc inside the motor cage, that is inside the cage and not removable
(for the record the jst is NOT at a standard pin spaces, at least I did not have the same in stock)
so I cutted the ntc cable, soldered another 100Ω ntc, and voilà... now it's working
it was only some 10cts component that was faulty.

hope this may help someone else.

[eutectique]

still the full module is available for ... 112 euros plus shipping !

I ordered a replacement board from festool, for some 140€ with shipping...

That's 25% inflation in 6,5 months.

[kripton2035]

112 euros plus shipping versus 140€ with shipping
difference is the shipping... and the more local seller...