Miele corded vacuum motor speed varies

[paltibine]

I've got a Miele cylinder vacuum that when turned on the motor spins up to almost full speed, then slows down, then speeds up again and just goes up and down. Obviously not much suction as the motor keeps slowing.
I've removed the hose, bag and all the filters and it makes no difference.

Anyone seen this before? I was thinking motor control PCB or is it likely to be the motor itself - brushes or bearings?

Thanks in advance!

 

[blup]

Capacitor?

 

[Propah Charlie]

Hello. Same problem here!

Paltibine, did you manage to sort it out? If so, what were the cause and the solution?

I have an old Miele S762, old but in good condition, or so I thought. Here's a video of the problem, same or similar to the way Paltibine described it: motor speeds up and down on its own (regardless of speed setting). Sometimes it works fine, up to max speed, even for long periods, then it randomly slows down and becomes variable again.

Tried some things: checked for blockages, ran vac without filters/bag, tried different electrical sockets in the house, took vac apart, took motor apart, inspected motor control circuit board visually and tested the 0.22uF box capacitor that some mentioned on other forums as a potential issue. Motor has soot in the windings (dust and/or carbon brush filings) but brushes are good; I quick-cleaned commutator segments.

Box capacitor was at 0.13uF so I replaced that to see if it helped. Initially, performance was golden for a few days - and I was well chuffed with myself - then it went back to its earlier up-and-down ways. So I'm not a genius...

If it were, say, an overheating issue, it should just cut out altogether, no?

I've heard the triac can fail, though it looks fine, no visual indication it's blown. If it is in fact the motor, I can't even find a like-for-like replacement on the net (model MRG 710-42/2, 2000W)...

I'm trying to avoid shelling out £200-300 for a new Miele (e.g. C2 Complete Cat & Dog) which I can ill-afford at the moment. (Don't want to buy from another brand if possible, including the much-vaunted Henries which look like plastic toys, are heavy and not practical for stairs - of which we have quite a few.)

Any help appreciated!

 

[Propah Charlie]

I just wondered... Could faulty motor bearings (which I don't remember inspecting) cause this sort of problem?

 

[paltibine]

I'm afraid I didn't fix mine but put it in the attic for when I've got a bit more time.
If the capacitor fixed it temporarily it implies that there is something damaging that cap but I've no idea what.

Sorry I can't be more helpful.

 

[Propah Charlie]

Thanks for replying. Sorry to hear you didn't fix yours yet.

Good point about something damaging the capacitor; didn't occur to me. Hmm...

Did you find a good replacement at least?

 

[paltibine]

Regarding a replacement, I was given an old henry which works well enough to mean fixing the Miele isn't a priority, hence the Miele is still in the attic awaiting attention......

 

[Propah Charlie]

Just found out something potentially useful...

By completely blocking the hose with my hand (making sure the flow regulator on the handle is closed), the motor responds by 'hunting' (for the demand power) at a higher speed. Playing with this phenomenon by removing my hand and blocking the hose again 2-3 times brings the motor back to full speed in a relatively short time. So far I've met with success each time I've tried this and the vacuum then remains at the required power at least long enough to do some useful work.

What this might mean in terms of a potential fix, I know not...

 

[robinbanks]

Perhaps some automated mechanism/device that activates when the machine thinks it's blocked up, varying the suction to try and clear the blockage? Perhaps your blocking the pipe creates an excess vacuum that helps dislodge accumulated crap when you release your hand and there is an extra inrush of air? Worth a dismantle and clean?

 

[Propah Charlie]

Perhaps some automated mechanism/device that activates when the machine thinks it's blocked up, varying the suction to try and clear the blockage? Perhaps your blocking the pipe creates an excess vacuum that helps dislodge accumulated crap when you release your hand and there is an extra inrush of air? Worth a dismantle and clean?

As mentioned in my first post, I did all the dismantling, examining and fettling possible, including taking the motor apart. Vacuum worked fine for some days after replacing the box capacitor - charge capacity having been a little over 50% - but it 'relapsed'.

It completely stopped working the other day so I played with the power dial, found an apparent 'sweet spot' where it would start up a little, banged the machine Fonzie-style, tried my hose-blocking tactic, then it started up again. This time, I kept blocking the hose for a while longer; machine kept working until I was done hoovering.

I'm not fond of this arrangement, but if I have to faff a little to avoid buying a new machine for as long as possible, I'll put up with it to avoid the cash outlay, other things being more of a priority.

 

[robinbanks]

So might there be a variable resistor in your vac that would benefit from a bit of contact cleaner? You know like an old amp makes the speakers crackle when you turn the volume knob?

 

[Propah Charlie]

So might there be a variable resistor in your vac that would benefit from a bit of contact cleaner? You know like an old amp makes the speakers crackle when you turn the volume knob?

Worth a look. It might be as simple as a bit of grime/dust on the contacts. Thanks for the suggestion.