Bush F841QW resonance

[Al123]

 

I have Bush F841QW washing machine. It started shaking violently but only at specific parts of the cycle.  I have started watching it to figure out exactly what is happening. I teach control systems to engineering students and I recognise the machine behaviour as resonance but I don’t have enough experience to identify the faulty component and will appreciate your advice. 

 

The machine turns smoothly during most parts of the cycle including the spin section. No excessive vibration or noise. However, during certain parts of the wash and rinse sections,  the drum stops which is then followed by high acceleration from rest for a few seconds presumably to aide cleaning/rinsing. It is during this rapid high acceleration that resonance is happening. And this is not helped by the rapid acceleration resulting in  momentarily unbalanced load. I assume that the spring/damper combination was designed to minimise the amplitude of vibration if resonance happens. But clearly something has changed and the resonance amplitude is now significant.

 

I took the dampers out and there appears to be still some resistance or damping friction there and there is nothing broken. But I have no idea whether the resistance is of the correct level. The springs appear to be extended but I have no idea whether they are correctly or over extended. And this is where I need your advice.... how can I assess whether the spring / damper constants are still at design level. And whether there is some other factor that is causing this problem.

 

the dampers appeared to be friction only type dampers. Is it worth using a sealed  oil damper of the same dimensions? Are there any such replacements?

 

I will be grateful for all and any advice.

 

Many thanks.

[Whitegoodshelp (Andy)]

Hello. Are you sure it's supposed to do the high acceleration from rest? If it is part of the programming it should ramp up slowly and shouldn't cause the drum to bang around.

[Al123]

Thank you very much for your input. 

 

This is a very good question... I am not sure about the high acceleration from rest. All I know is that it is happening as part of the wash and part of the rinse section of the cycle. It doesn’t happen from every rest position but it does happen from some of them. I assumed it is by design. How do I check?

[Whitegoodshelp (Andy)]

I would hope it mentions it in the instruction manual. Hoover washing machines used to do this about 20 - 30 years ago but they abandoned it I think. A fault could cause it to lose control of the spin. 

I would say if it goes straight into a spin from standstill and thumps around that’s not right. If it seems fairly controlled and increases speed to gently do a short and slow spin it could be by design. 

[Al123]

It doesn’t do high acceleration from rest during the spin section of the cycle. It does it during the wash section and during the rinse section. When it comes to the spin section after wash and rinse, there are no problems.

 

there is nothing in the manual about high acceleration from rest during the wash and rinse sections of the cycle.

[Whitegoodshelp (Andy)]

Any chance of a video of it? It’s possible for a fault to cause motor to surge and go out of control intermittently. 

[Al123]

Thank you. I will put it together on Tuesday and do a video.

 

You make a very good point. what kind of fault would cause the motor to have high acceleration from rest only on specific parts of the cycle?

[Whitegoodshelp (Andy)]

It's probably less common these days but it used to be quite common on various different brands. There is a TOC built into the windings of the motor. Sometimes a TOC would cut out, but then cut back in as it cooled down. When it cut back in, if the motor was receiving power it would suddenly surge until the control module regained control. Also, dry joints or overheating issues in the module that controls the speed of the motor could cause this to. And old Hoover and Hotpoint washing machines with mechanical timers used to get a fault on the motor switching switches inside the mechanical timer responsible for reversing the motor during wash and rinse cycles could cause the same fault. However, the nature of the faults I describe tend to manifest in fairly random surges as you can imagine.

[Al123]

Thank you so much for your input.

 

what is TOC and if this is the problem, how can it be fixed?.. incidentally, the machine is less than four years old.

 

i will post some videos sometime tomorrow.

 

many thanks.

[Al123]

There is a limit of 0.98MB on file size upload. The videos will be above this. How do we overcome this? Can I email you the files?

[Whitegoodshelp (Andy)]

Yes try emailing it to me please. There's a contact form accessible from a link at bottom of page.