Miele washer/drier wt945-Electronic Control Unit EPW 900

[nucleardave]

This pcb includes the level/pressure switch and the selector switches for the wash and drier options. A fault developed where many options were introduced out of sequence etc. Has anyone sourced a replacement level switch or worked on this pcb? Many thanks.

 

[yardie]

You should be able to test whether the pressure switch is functioning or not. If its ok the board then needs further investigation or replacing.

 

[lavo-1]

The PCB on those are very reliable and I would be surprised if that was at fault. The pressure transducer on the board is also a very reliable unit, so I am wondering why you have concluded that this is at fault.
You said your options where out of sequence? What I know off that model is that the electronics have a self diagnostics software function and the display LED's maybe trying to indicate a fault with a corresponding error code for the service technician. This may look to you as a "out of sequence" display.
The Miele are probably one of the most complex appliances for the DIYer to repair as the electronics and embedded software are not easy to decipher with out prior knowledge of the service programs used by their technicians.

 

[nucleardave]

Thanks for the above replies. So here comes the detail: I noticed that there was no spin cycle during the rinse stage and also at the end. It was not possible to turn off the machine and the 'finish' alarm continued. By opening the door and closing it a bit more forcibly the led went out and the selector switch was returned to 120'clock and turned off. Thereafter a 60deg. wash was done and again no spin apart from the initial 400 at the start. However, a separate spin cycle worked fine. Subsequently, there was an exponential deterioration in the process. Prior to next usage, the drain pump, hoses were all checked and as expected all very clean: I had cleaned this system and examined it previously during a condenser/ leak tray fault. I also examined the plenum connected to the drum and the hose to the pcb that is the basis of my question, all was clean. Subsequent use resulted in inability to turn off the program, so on turning the machine on and when the door was latched the finish alarm would sound and the drain pump run as thought attempting to finish the previous wash cycle-the selector still being at 12o'clock. Testing of the door relay showed it to be working correctly.
I bought a used washer on ebay that was sold for parts and not working and changed the pcb that is the basis of this thread. A trial this morning showed that only the led for on was indicated-as opposed to the earlier scattering of drain final rinse end of programme indications previously. A 60deg cycle has run through with an apparent increase to 1500rpm9I thought it only ever operated at 1200 unless selected). Alarms cancel at finish and on a trial of this and fluff removal, we seem to be fully operational again.
So why ask? Well the ebay washer will be a similar age and hence the fault might reappear-we are talking 12 years old. I want to determine the component fault rather than doing a substitution as so many of our technicians seem to do ( with the edifying finale of cost of call out time and part replacement cost and finally having parted with the cash and suspecting they could probably only guess at the failure tell me 'it's not worth repairing..'
Finally, testing the pressure switch: it's often said that if you blow down the spout into the switch/diaphragm and don't hear a click it's failed. Neither mine nor the one on the replaced board do so. There are four terminals. The switch is made by Miele.. Looking forward to hearing from you and further on fault trees, reliability and problem solving.

 

[jj4091]

Finally, testing the pressure switch: it's often said that if you blow down the spout into the switch/diaphragm and don't hear a click it's failed.

Only if you have a electro mechanical switch. You may have to check voltage input & output.

 

[lavo-1]

Its not a switch its a transducer that changes its value with pressure. Miele did away with the 2-3 stage pressure switch many, many years ago.

 

[nucleardave]

Yes, a transducer. But, my guess is that it's the selector for the various wash cycles but certainly heaters coming on and drain pumps running with alarms was quite a spectacle until my board replacement. I presume that all this has been replaced by solid state in later models, although I notice plenty of questions of flashing leds, no spin etc etc. So much for reliability: few-if any- manufacturers would have the resources to fully model all the fault sequences and design and manufacture components to the required reliability and that would include considerable qualification programmes. Looking forward to hearing more insight into the Miele electronics fault analysis. Regards to all.

 

[jj4091]

The pressure switch detects the water level/presence in all machines, they won't start any wash programme until water is present, & perhaps even affect the spin mode ( that I am not 100% sure about )The heating element should definitely not be supplied if there is no water present. Sorry I cannot help you with the electronic circuitry of Miele machines

 

[nucleardave]

Many thanks for the comments so far. Just to summarise and hopefully garner more thoughts, swapping of the EPW 900 has appeared to solve the problem of multiple and erratic operations and inability to cancel the finish alarm except by pressing the on/off button. So far a full wash cycle was completed without any untoward behaviour. Today, I used the 20 min dry cycle that introduces water for the condenser and rotates the drum and uses the fan and associated heaters-all seems to have gone correctly to the end of cycle. I have attempted to put the 'faulty' EPW 900 into the Miele 945 I bought for spares. Whilst there is power in and to terminals 2 and 3 on the switch pcb when the door switch is latched and ON pressed there is no power to EPW 900 as evinced by an unlit LED that indicates 'on'. Further examination shows that of the four spade connector from the switch pcb to EL140A ,that does much of connecting of motors and valves etc. , only the first carries 240v, whereas I expect from earlier examination that most would. I believe that one of these cables provides power through the door relay to the 900 unit that holds the selectors and LEDs etc. Of course what I was hoping was that on insertion of that suspect 900 from my machine to the one 'for parts' I would end up with the same alarms and malfunctions. So helpful readers what more might I do: or is the angle grinder awaiting.. Regards to all, David.

 

[lavo-1]

Those boards had different versions and also the PCB has an Eprom that would be programmed by the service technician to what variant its was to installed into. There may or may not be a fault on the PCB, but rather it needs to be hooked up to the Miele programming software (Miele Tech required).
Glad you got it going, well done.

 

[nucleardave]

Many thanks for last advice. I obviously am concerned when not repeating the fault sequence that I have not really identified what went wrong; but if after today I don't get further then I suppose all that can be done is to rely on the fact that the more the machine is used and remains fault free the greater confidence I shall have. At the moment something tells me there is more involved. The Eprom etc. was interesting since with cars many of such devices are coded and cannot be substituted as I have done, so at least that seems to have been lucky. Of course what we can't do is buy a cheap diagnostic tool to run the faults down. Following this logic could lead to buying cheaper machines of course-but without the fun of problem solving! Regards to all.

 

[nucleardave]

A few final observations: With the 'on' switch made and the door latched and the door interlock (3 brown cables) disconnected the spare machine shows (like mine) 240v to the electronic unit 140A and the fourth of this set of four has 240 return to the switch pcb. At this stage it is not possible to mimic the 'finish wash' alarm or any of the spurious operations. However, if the four-cable ribbon from the base of this pcb (this has two connected and on pressing door release all four are connected (35v) is disconnected from the front board 90A then the alarm sounds and the light for ON comes on. With the four cable ribbon connected the 240v return mentioned above disappears and all is quite silent (but not dead). YDes, I have succeeded by obtaining and swapping the board (90A) and consider myself lucky; but have not determined the fault.
Incidentally, my theory about the selector switch shows my age: there are not metallic contacts at the switch, it all done by leds and a reflector in the back of the knob. This is presumably an excellent electrical safety device.

On another theme, I note that at the end of the drum shaft there is a carbon brush and brass wire connected to the shaft. Is this part of a Ward Leonard system-ha ha.
Regards to anyone interested, (I cannot see much more mileage in this thread.)