Bosch WM drains ok, begins to spin but stops

Hi Andy, old brushes had worn away about 70% but were shiney and ok. You’re right, I didn’t check them prior. On a wash cycle it fills with water and drains ok but again doesn’t spin properly. Starts to spin fast and then motor shuts off right away. It slows and then skips cycle. So on a wash it’s not turning either ( The drum spins freely by hand) The 12minute spin cycle tries 3 times to spin and is over in 40 seconds. I’ve just been running the spin programme to test it. Motor Connectors and pins all secure. A little sooty but assume carbon from brushes and wipes off. No blockages. It was stored for 8months as we renovated house but was ok last 3 weeks. Trying to avoid new WM as brassic after new kitchen☺️ Thanks for the feedback.👍 Mick

Hi. If the motor spins fast (surges) instead of a slow controlled turn, and then stops, that sounds like it's lost control of the motor. This can be caused by the tacho coil or magnet, or potentially a pcb fault. Normally though, these days if the tacho coil or magnet fail it should cut the motor but some may still do the surge and stop behaviour.

Have a look at this article to understand how the techo coil and magnet work. The most common cause is when the magnet comes loose or broken or drops off. If it isn't that I wouldn't recommend speculatively replacing any parts - especially the pcb.

If this isn't what it's doing please explain a bit more for me.

Actually this article might be better, but read them both tacho coil

Cheers Andy, just home and had a quick look. Magnet and tacho coil are where they should be and not loose. It is a surge like attempt to spin , like someone revving a car. Short vid attached. I think I’m in over my head so prob need a pro in! Thx for the great advice pal🙏😉

IMG_3136.MOV

Thanks for the video. Yes that's exactly what I suspected. There's a loss of control over the motor. If the tacho cool and magnet look OK you'd need to do a continuity test on the tacho coil. However, they have a very high reading that almost looks open circuit. If it is open circuit then it could be that. After that it's the connections to the tacho coil on the motor plug, and from the plug to the pcb.

Hi Andy, I'm only getting 22 ohms resistance across the tacho coil pins. That was a pretty steady reading but had a few intermittent jumps upto 50,60 and 100. Connections to the tacho coil on the 6pin motor plug are good. I haven't checked plug to the pcb yet. Cheers, Mick

It's a long time since I tested one. I just remember they were usually very high resistance stopping just 5 mm short of open circuit on my mega. Essentially they are very long thin wire wrapped around. The only faults I ever had on them were when they went open circuit. Occasionally you may have one that goes open circuit when you move the connections but generally they would just go open circuit. It was also extremely rare to find any that were faulty because they are not subject to any movement, or high current, so they were a very reliable part. Overwhelmingly, the most common cause of problems in this area was a loose tacho magnet or broken tacho magnet.

Thx Andy. I think we'll bit the bullet and replace. Not seeing tacho sold seperately (Not 100% it's tacho) so for the cost of a whole motor may as well replace with new machine. it's done 13 years hard graft. Great website- very helpful and very knowledgeable. I learnt a few things anyway! Much appreciated

Hi, yes you can at least be happy in the knowledge that you had a good look and you are not throwing it away because of some easily fixed problem. There's only so much you can do without the knowledge, experience and training.