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Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 5th Oct 2019, 5:43 pm   #1
robinshack
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Default Kärcher WV75 Plus window vac that died.

Had this about 5 to 7 years and always been ok. Occasionally, if tilted down or sideways (like you sometimes have to do near a windowsill) you could hear that there was water got into the fan blade and sometimes a bit of spray from the air outlet slots. I never thought this was a good thing and yesterday, it would not power on at all despite a full charge.
I decided to carefully take it apart after trying "banging" it near the switch, which was one google result!
I used an old bath towel on the kitchen table so as to stop things sliding about. This was because my workshop is in need of a blitz as there is just a few square inches of bench space left on my tiny workbench!
The screws looked as if they had ominous non standard torx like heads. However, a small flat blade fitted across 2 slightly larger slots of the six provided, a little like torx, but not the same. Never seen these before.
I found that the pcb component side (SMD ics etc) had some green furry corrosion all around one 8 pin chip. I first un-soldered the 3,6V lithium battery wires from pcb then cleaned up the affected area with ipa and a toothbrush. I also soldered a "u" wire link through two vias, one of which was black with corrosion.
Cautiously, I wired to my bench psu set at 3.7V. It ran at about the correct speed for less than a second, then stopped. It was drawing 4A. I tried slightly different voltages, still the same results.
So, I then reconnected the battery as a last resort and it worked correctly.
I can only assume it didn't like the 5 -6A max of my bench psu?
I then sprayed both sides of the pcb several times with some RS Conformal coating that I have had about 15 or so years. Allowing to dry between each coat. I always knew It would have a use....one day!
I applied fresh grease (multi purpose lithium based car grease) where the original was, as it is used for waterproofing the compartment seals around the motor and pcb part. I had taken several pictures earlier as it looked quite confined inside. Well worth it I found.
Whilst apart, I also dismantled all the suction blade and inlet assembly and cleaned it out. One tip I recommend when re-assembling is to apply a small amount of grease to the self tapping screw threads as it makes re-insertion into the plastic and tightening much easier, bearing in mind the non-standard screwdriver I used to rotate them.
Most difficult part was routing the switch wires upon re-assembly.
So, I saved around £45-£50 cost for a new current model.
Rob
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Old 6th Oct 2019, 10:41 am   #2
Herald1360
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Default Re: Kärcher WV75 Plus window vac that died.

Multipurpose lithium grease is soap and oil and is unfortunately water soluble (at any rate the soap bit). Silicone grease is much better for waterproofing jobs like this and won't attack rubber either.


You did better than my efforts last week at a repair cafe- after unseizing the motor, waking up the overdischarged battery with a PSU and series resistor (the high current yours took was just the battery recharging when its voltage dropped a bit) and cleaning off the PCB, the switch / control circuit refused to play so it ended up as WEEE.

(Like lead acid cells, LiIon ones need a current limited constant voltage supply for proper charging. A PSU and series resistor is OK if the initial current is reasonable and you watch the cell voltage (don't exceed 4.2V) carefully. OK to see if an overdischrged one will "wake up" but not recommended for regular charging.)


One tends to detect a whiff of planned obsolesecence in toys like these that deal with both electrics/electronics and water in the same box......
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Last edited by Herald1360; 6th Oct 2019 at 10:48 am.
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Old 6th Oct 2019, 10:45 am   #3
paulsherwin
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Default Re: Kärcher WV75 Plus window vac that died.

Ordinary vaseline is better than automotive grease for sealing and waterproofing.

These motors running on just 3.6V can indeed pull a surprising amount of current.
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Old 6th Oct 2019, 1:49 pm   #4
robinshack
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Default Re: Kärcher WV75 Plus window vac that died.

OK, thanks for the comments.
Chris, the psu was connected instead of the battery, but only once I had cleared the corrosion.
The original grease had the yellow/brown colour but seemed quite thick. If it goes faulty again in a few years, I will indeed try Vaseline. I don't think I have any silicone grease these days since I had started using white heatsink compound years ago. I used to have a tube of MS4, but not been seen for years now.
When I first dismantled it I hadn't seen the corrosion on the pcb. I checked battery voltage first and then the motor for continuity and by rotating it a little it generated a small voltage. Then I progressed to the pcb and saw the corrosion.
Rob
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