Beko WMC126W- motor problem

[Bekokid]

Motor/Engine will not drive the drum.

Removed belt, motor attempts to move approx 5 mins of a clock face in each direction then a burst of speed and free runs to a stop.

Removed the motor, armature and field show between 1.0 & 3.0 Ohms. But sensor shows 114 Ohms where think it should be approx 3.0 Ohms.

Are these sensors replaceable if this appears to be the fault ? 

[Whitegoodshelp (Andy)]

Hello there. I'm not aware of any sensors on the motor, there's usually just armature, field coil thermal overload cutout (TOC) and a tachometer coil. It's rare for any individual parts to be available for a washing machine motor these days. You can usually buy carbon brushes, but commonly that's it. I've even known some motors in the past where you couldn't even buy new carbon brushes.

[Bekokid]

These images of the sensor at rear of motor

[Whitegoodshelp (Andy)]

Hi. Thats the tacho coil. It should have a very high resistance, almost open circuit. You can learn what it does here - What is a tacho coil? In my experience the tacho coil is usually either giving a reading just off open circuit, or totally open circuit.

A washing machine motor should always start turning very slowly and gradually increase in speed. If the motor spins at fast spin speed for a few seconds right from a standing start, it can be caused by a broken or very loose magnet inside the coil. Many of the magnets are held in place by some sort of clip that once taken off won't fix back, so be careful. See if you can see the magnet under the round plastic part in the centre.

[Bekokid]

So is 114 Ohms high or low for this coil or faulty. 
When the machine is asked to do a simple function as Spin and Drain. The pump starts to empty, the motor moves in each direction about 3/5 mins on clock face then has a burst of speed for a second or two then runs down to a stop.  After 15/20 seconds it recycle itself starts again over again.

[Whitegoodshelp (Andy)]

If the motor turns at normal speed as well as fast spin, it shouldn't be anything to do with the tacho coil or magnet. With faults on the tacho coil and magnet, the pcb loses all control over the motor speeds and can only make the motor spin or the motor goes dead.

I can't remember the readings on a tacho coil, but on my old mega the needle shot right over to infinity, but stopped about 2 or 3 mm short of it. The coil is a very thin and very log coil wrapped, so it's hard to imagine how it could ever be anything like fully in tact with a high resistance reading, or with a break in it somewhere, which would give open circuit.

If the carbon brushes are ok I would look for some dodgy connection on the motor, motor plug and motor harness. Other than that it could be a fault on the PCB but I wouldn't get involved with that.

[Whitegoodshelp (Andy)]

I would add that if the motor always does exactly the same thing then it's unlikely to be any connection fault, which you would expect to be more random.

[Bekokid]

With the belt fitted the motor will not move the drum,  just attempts to move in either direction a fraction of amount only.

With the belt removed motor only moves as described previously.

The motor will not run in any program as normal turning the drum as if washing or spin.

[Whitegoodshelp (Andy)]

Are the carbon brushes ok?

[Bekokid]

Yes, when released. They are 30/35 mm long.

With these results which appear to show no major issue.

Could it be the PCB board at fault not controlling the motor ?

[Whitegoodshelp (Andy)]

It could need a complete new motor, or a PCB. There's no way to be sure which one. I can only advise that if you can't find any poor connections and the brushes aren't charred that you've done all you can. You can get faults where the motor won't turn under even the load of an empty drum caused by faulty field coil, or armature in the motor, or faulty parts inside the PCB. Just buying one of thee very expensive parts and hoping it fixes it is not really a sensible option.

[Bekokid]

Ok 

Still same issue using diagnostic routine and from earlier tests showing no major faults with the motor.

I removed the control board and found areas with burning residue around a capacitor solder joints and diodes.

The board number: 2839630100

 

[Whitegoodshelp (Andy)]

I could be wrong, but that looks like the kind of black soot that is on most pcbs or modules. Does it wipe off? If it does, it’s probably not burning, just black dust/soot caused by heat (usually from resistors)

[MelS]

My brother who knows a lot more more about electronics than me, tells me that could be caused by a dry solder joint, the resistance causing it to get hot, so the joints could probably use touching up, but might not be the cause of the fault. 

 

My own electronics knowledge is very basic, but I would guess that the most likely component to cause a motor fault would be the triac for the motor speed control, which I would expect to be located on a large heatsink, probably the largest on the board.

The triac on mine controls the power to the field windings, the motor armature is controlled and reversed  by a pair single pole double throw relays which switch the connections to the armature, when both are on or off, both brushes will be the same polarity so the motor won't run. (There's also a third relay which switches out half the field coils to speed up the motor).

So another possibility is a faulty reversing relay, the contacts in one of mine stuck "welded" on, although mine identifies that fault and refuses to run, A few gentle taps can temporarily fix that.  

Looking that board number online there are a lot of used, claimed working  boards for sale quite cheap, however you need one which matches all the codes on yours as different revisions with that number seem to be used on different machines and wouldn't be suitable for yours, I would check a decent spares website for your model and serial number to find if there are any alternative compatible boards.

 

 

 

 

Edited October 20 by MelS