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Old 23rd Feb 2020, 2:03 pm   #1
phildil
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Default Zanussi Dishwasher DW904 Timer

hello all

My vintage dishwasher, a Zanussi DW904 made in 1991, has just this weekend developed a fault. The timer dial has stopped rotating and the washing programmes therefore will not advance. The machine still washes but the dial now has to be rotated by hand (!) in order to move the cycle along.

This dishwasher is controlled by a mechanical timer assembly located behind the control fascia, where a small motor drives a shaft on which a series of cams rotate and, as time progresses, switch the various parts of the machine on and off. From my fault finding this morning, it seems that this motor is no longer receiving power, and thus has stopped rotating. The power comes from a location somewhere inside the machine; there is presumably a step-down transformer underneath the tub. My question is, what voltage is this motor expecting? I have tried giving it 12v DC but nothing happens.

All infos welcome
thank you
Phil
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Old 23rd Feb 2020, 3:30 pm   #2
rambo1152
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Default Re: Zanussi Dishwasher DW904 Timer

I think these programmers use synchronous AC motors. I would expect it to work on full mains voltage.

Did your testing include checking for AC across the motor?
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Old 23rd Feb 2020, 4:51 pm   #3
Nickthedentist
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Default Re: Zanussi Dishwasher DW904 Timer

And check the timer motor for continuity (a few kOhms, power off of course!).
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Old 23rd Feb 2020, 5:27 pm   #4
duncanlowe
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Default Re: Zanussi Dishwasher DW904 Timer

Washing machines certainly used synchronous motors to drive the timer, and those do fail. They used to be a fairly standard size and you could get replacement motors to clip on.

Here's a picture of a typical washing machine timer, with said motor (listing only used as a convenient source of an example picture).
https://www.ebay.co.uk/itm/Washing-M...AAAOSwB09YNln-
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Old 23rd Feb 2020, 9:53 pm   #5
Richard
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Default Re: Zanussi Dishwasher DW904 Timer

Hi

Circuit diagram for the DW904/A machine.
Timer is no longer available

Richard
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Old 23rd Feb 2020, 11:28 pm   #6
phildil
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Default Re: Zanussi Dishwasher DW904 Timer

Hi all

thanks for the infos. An update:

Yes I did test for AC across the motor supply and there is no voltage there, either AC or DC.

The impedance across the motor (with power off) is 8.93 KOhms.

Richard - Thanks for the circuit diagram - where did you find this ? I would like to get a hi-res copy.

A synchronous motor would make sense - would it definitely be 240V ?

cheers
Phil
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Old 24th Feb 2020, 10:42 am   #7
simpsons
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Default Re: Zanussi Dishwasher DW904 Timer

Phil

From my experience it is the sensors which allow the timer motor to run which are most likely to fail. For total non running, this includes but are not exclusive.

1. The door switch

2. Water inlet valve

Other members have posted threads on their dishwashers which can be searched on this site.

Should I find further info to help I'll get back in touch.

Good luck

Chris
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Old 24th Feb 2020, 11:10 am   #8
Nickthedentist
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Default Re: Zanussi Dishwasher DW904 Timer

I agree with Chris.

You seem to have a working timer motor, but no supply to allow it to advance the programme. Note that the supply should not be there permanently, only when the rest of the machine has done what it was meant to be doing on that part of the programme.

So check all the other peripheral bits and bobs, and don't waste your money trying to source a replacement timer.

N.

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Old 24th Feb 2020, 12:15 pm   #9
phildil
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Default Re: Zanussi Dishwasher DW904 Timer

A Monday Morning Update from the kitchen:

Connecting a separate 240v supply to the timer motor results in a successful wash cycle. After the wash has completed, the machine shuts off as usual and the timer motor idles. So yes, as suggested earlier, one of the sensors has failed. The door latch tests OK so I suspect either solenoid valve or float switch.

meantime there are various other parts requiring replacement: neon (easy); door lower seal; front fascia.... Of course I *could* just buy a new machine, but....

thanks all for input

cheers
Phil
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Old 24th Feb 2020, 12:25 pm   #10
simpsons
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Default Re: Zanussi Dishwasher DW904 Timer

OK

Dishwashers seem to all work in similar way, as expected and often share the innards from other manufacturers or are simply branded.

In your instance it is before the use of microprossesor controls which can complicate matters.

Your model's service manual is available online on a 30 day free trial but to get you started, I attach the Bosh which is a similar design although you will see it has a delay timer.

Just remember, when working underneath, these machines are heavy; don't forget to disconnect from the mains supply; most terminals will have a plastic insulation sleeve so use a test meter probe accordingly. Start at the on/off switch and follow the wiring loom which will be colour coded.

Chris
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Old 24th Feb 2020, 5:17 pm   #11
phildil
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Default Re: Zanussi Dishwasher DW904 Timer

Ah yes I did see that the DW904 service manual was available for download from a decidedly dodgy-looking website which invited me to merely enter my credit card details .... erm no thanks.

Anyway, the fault was a thermal cut out located under the tub, which was stuck open. Removing, cleaning and replacing it has done the trick. Back up and running. Phew. No washing-up for me then.

cheers all
phil
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