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I just changed the pump on another of these machines and the impeller was larger and a different shape to mine. Maybe askoll supplied a batch of pumps to zanussi with the wrong impeller?
Martin wrote:New controller? Engineer out? Could I please ask you to elaborate? 🙂
The machine was in a show house in one of Irelands many ghost estates so even though it was basically brand new it was out of warranty. The estates developer sold off the appliances to pay the bills and the new owner had problems from the get go. A repair man was sent by zanussi who said the pump was fine and that the machine needed a new pcb. I was given the machine for free as the pcb was too expensive.
Martin wrote:
we in the trade have a more effective method of overcoming the problem, namely replacing the faulty pressure switch and clearing the sludge from the pressure chamber and hose system!and you’d have wasted your time there was zero sludge as it was used for about 2 weeks and the pressure switch output was *exactly* the correct frequency the previou owner had the engineer out who decided it needed a new controller
Re: analogic pressure switch frequency
While a pump may solve the issue in the short term the pump is not the problem, my pump still empties the washing machine quickly and I expect to get another few years out of it.
The root of the problem is that the programmers haven’t allowed enough tolerance in reading the pressure signal.
I found that a difference of just 0.2Hz which is equivalent to about 4mm of water in pressure terms was enough to tell the machine it was empty thats not enough margin.
Re: analogic pressure switch frequency
The switch utilises a diaphragm pusching a ferrite into an air cored inductor. This forms part of a tuned circuit attached to a 12f629 pic which converts the signal into a remarkably linear output.
0mm of water is 44.75Hz – 300mm of water is 36.2Hz you can draw a straight line between the two to extrapolate the output graph. The machine expects a frequency lower than 0mm due to the slight vacuum created by the drain pump.
My initial thought was to take a couple of coils off the inductor to adjust it or stretch the internal spring but I thought I might get a pump at some stage and need to return the sensor to original. Instead I decided to replace the smt capacitor in the tuned circuit.
I don’t have an lc bridge so I estimated the required value by measuring the output with a 220p capacitor and a 10n capacitor. I estimated 760p which I didn’t have so I made by stringing 1n, 4.7n and 10n in series and the result was almost perfect. Washing machine now overfills slighty but works perfectly.
I measured the frequency with a multimeter, no need for an oscilloscope.
Re: analogic pressure switch frequency
I found out myself the sensors 0mm (empty) frequency is 44.75Hz I assumed it would be in the kHz range as in industrial equipment. Full frequency is 42Hz.
The designers factored in the slight vacuum created by the pump into their empty calculation. As the magnet in the pump gets weaker the vaccuum decreases and the computer assumes the machine is not empty. My pump works perfectly so I changed the tuned circuit in the pressure switch (transducer) to compensate.
