AEG T37400 Tumble Dryer - won't start

[Johnking]

This is a crosspost from ukwhitegoods, where nobody replied - hoping for a bit of luck here!

My old dryer has been used daily since 2005 and owes me nothing. But a new dryer is £500 so I'd like to fix it. But I've run out of ideas.

The symptom: When the start button is pressed, there is a slight bump from the motor, but nothing else happens.There is no humming.

Diagnostics so far:

1. The 8uF capacitor had failed (reads 1.7uF). I replaced it, but the problem remains the same
2. Sensors all seem fine
   • two Elth brand bimetalic thermostats in the heater are both showing continuity
   • temperature sensor in the drum has low resistance which changes in response to warmth
   • drum sensor brush has good connectivity
3. Switches seem fine
   • Door switch working
   • Power button working
   • Program selector seems to work - e.g. it resets the system OK
4. Connectors all in good condition and firmly plugged.
5. Control board has no obviously damaged components (capacitors are fine)

The elephant in the room, of course, is the motor, which I struggle to understand. It is a single phase AC motor which seems to be used across a wide range of dryers, type CK-302300-21R01. I have gathered the following information:

1. Resistances
   • R 1:3 = 28 Ohm
   • R 2:3 = 29 Ohm
   • R 1:2 = 56 Ohm
2. Behaviour
   • All the above go open circuit when the motor turns. Centrifugal switch?
   • On start, there is a small jerk of the motor, but only enough torque to twitch the drum before it stops
   • I tried turning the drum while pressing start. I have done this many times and it does nothing apart from once, when the drum started spinning, the heater came on and it appeared to be functioning normally. To prevent the heater blowing, I powered off immediately. I have not been able to reproduce this.

What next? Motors are >£100 so not something I'd take a punt on. I'm confused by the motor - why do ALL the resistances go open circuit when it turns?

I'm pretty stumped! What can I try next? I have a simple digital multimeter, which includes capacitance and current clamp, but nothing else.

Many thanks,

JK

 

[blup]

Capacitor failure, need to re check new capacitor?

Blup

 

[Johnking]

Capacitor failure, need to re check new capacitor?

Blup

Seems fine, reads 8uF on my meter.

 

[jj4091]

You seem to be happy to work on a live machine so the only thing I can suggest is to check for a voltage at both sides of the capacitor to neutral or earth when the motor is switched on. If that is ok the it does sound like motor may have failed. Used ones seem to be available for a lot less than £100. Also have you checked the door switch is OK.

 

[Johnking]

Thanks, will try. I know that there's no voltage on the motor terminals other than for a moment when it's turned on.

The motor did run one time which makes me think the motor is ok, am I wrong?

 

[jj4091]

If there is no voltage ( presuming you are checking with a multi meter) at the any of the motor terminals & there are no broken wires back to the pcb & door switch & wiring are ok then I would suspect the pcb is faulty even if there are no obvious failed components. If there is a relay on the board that could well control the motor & you could not tell by looking at it if it was faulty or not, but it could be a replaceable item. You would need your PNC. No.to find the right one & if they do not come preprogrammed you will need an AEG engineer to do it. May not then be a cost effective repair.

 

[Johnking]

If there is no voltage ( presuming you are checking with a multi meter) at the any of the motor terminals & there are no broken wires back to the pcb & door switch & wiring are ok then I would suspect the pcb is faulty even if there are no obvious failed components. If there is a relay on the board that could well control the motor & you could not tell by looking at it if it was faulty or not, but it could be a replaceable item. You would need your PNC. No.to find the right one & if they do not come preprogrammed you will need an AEG engineer to do it. May not then be a cost effective repair.

There's deffo a relay, I can hear it clicking, I can test it. But is a lack of sustained voltage at the motor what we'd expect? It had assumed the board might be (correctly) turning off the power in response to a detected fault.

It's really frustrating; I'm happy to invest in keeping this thing going, but I want to be sure I'm getting the right spares.

Is there anything to gather from the fact the capacitor HAD gone, but that hte problem persists? Could both be a symptom of something else, or could the capacitor have blown in a way that damaged something else?

 

[jj4091]

The relay clicking only indicates that the coil is ok not the contacts so if it is calling & you can trace it back to being the supply for the motor, you would then need to find out if the contacts are conducting a voltage to the motor, if not then that could well be your problem. On the other hand it might well be that some other error is turning off or not switching on the motor as you say. But one would assume it would do that by not calling the relay. That I cannot help you with, trying to guess things like that without a circuit diagram or the experience to know is impossible. Capacitors do fail for no reason other than ageing sometimes, so I don't think that nessacarily indicates another fault, but again it is a possibility.
Had you thought about what AEG charge for a callout, some companies have an all in parts & labour fee which may prove more economical if you want to keep the machine going

 

[foxhole]

Does the drum turn by hand ? What’s the state of motor brushes.

 

[Harry Bloomfield]

Is the drum perfectly free to rotate?

It reads as if it is detecting some sort of fault on the motor or drum, and so shuts down to avoid damage.

 

[Johnking]

Does the drum turn by hand ? What’s the state of motor brushes.

It does, and indeed on one occasion it ran from me turning at the same time as pressing the start button.

I think the motor is brushless

 

[Johnking]

It's as free as it's ever been.

Is the drum perfectly free to rotate?

It reads as if it is detecting some sort of fault on the motor or drum, and so shuts down to avoid damage.

 

[Johnking]

The relay clicking only indicates that the coil is ok not the contacts so if it is calling & you can trace it back to being the supply for the motor, you would then need to find out if the contacts are conducting a voltage to the motor, if not then that could well be your problem. On the other hand it might well be that some other error is turning off or not switching on the motor as you say. But one would assume it would do that by not calling the relay. That I cannot help you with, trying to guess things like that without a circuit diagram or the experience to know is impossible. Capacitors do fail for no reason other than ageing sometimes, so I don't think that nessacarily indicates another fault, but again it is a possibility.
Had you thought about what AEG charge for a callout, some companies have an all in parts & labour fee which may prove more economical if you want to keep the machine going

Interesting thought about the callout. I know they sell spares, maybe it's possible to return them if not required.

 

[Johnking]

I'm an idiot!

It was just a duff capacitor, but I'd forgotten there's a 30s timer between pressing start and the drum turning. I just wasn't waiting long enough.

 

[Harry Bloomfield]

It was just a duff capacitor, but I'd forgotten there's a 30s timer between pressing start and the drum turning. I just wasn't waiting long enough.

That 30seconds will be the delay between it switching on the door lock, and it getting back the 'door locked' signal. They use an electrically heated wax cylinder.