Bosch washing machine burned out capacitor and transformer...

On Mon, 10 Nov 2008 11:42:35 -0800 (PST), snipped-for-privacy@tesco.net put finger to keyboard and composed:

Are there any visual indications that suggest that the CPU *thinks* that the washing machine is in its rinse cycle?

The 400V capacitor is probably the bulk capacitor which filters the output of the mains bridge rectifier. If the power supply to the CPU is working, then this cap is probably still functional, although if it is visibly leaking or swelling, it should be replaced.

Hmm, so it's not a transformer, but a coil, or choke. What does it connect to?

BTW, uploading a photo to your web space might help.

- Franc Zabkar

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Franc; Thanks for responding.

No, there are no visual clues to suggest that it thinks it is in the rinse cycle. In fact, it shows a constant "1 minute remaining" of the wash cycle. The wash cycle never actually finishes - that 1 minute lasts longer than I can!

I've been pondering these things and I'm a bit stuck as to what the problem really is.

I've not re-checked the circuit as I have put it all back together so I can still wash things but...

The machine is mostly working so the power supply to the controller must be fine Though why I would have a 400V capacitor (actually 22uF) after the rectifier in a supply for a controller (say 5 to 24v) is a bit puzzling (I know - I really must look at the circuit again)

Also, I now believe that the transformer is a pulse transformer for controlling the motor through a triac though, I reiterate, I have not checked the circuit. But, if it is controlling the motor, thats working fine so it can't be that either.

Something I forgot to mention was that it looked like the circuit board had burned a bit along the track that joins the transformer to the triac (?) but I'm not too sure if that has caused the problem either.

I'm wondering whether I should just change the capacitor and look for alternative reasons for the failure to switch to the rinse cycle. Is this capcacitor likely to be a non-polarised version or just a plain electrolytic?

I know what you mean about a photo - when I next have it apart I might post one somewhere - not too sure where but I'll find somewhere I'm sure.

Now, does anyone know a resonably priced source of 400V 22uF electrolysic capacitors? :-)

I applaud your trying to fix this yourself, but a visit to the nearest store that sell the machines and maybe has a repair serivce might be worthwhile. I personally will not buy any machine that has an electronic control, only machines that use a mechanical timer that rotates and makes and breaks contacts as it rotates. I know the electronic timers (should) work a lot longer, but they are almost impossible to fix if they do go kaput, and hence my aversion to them.

Bob Hofmann

On Tue, 11 Nov 2008 13:07:33 -0800 (PST), snipped-for-privacy@tesco.net put finger to keyboard and composed:

It sounds like the CPU may be looking for output from a sensor.

This is a switchmode PSU out of a cheap DVD player:

Notice the 22uF, 400V capacitor (E1) at the bridge rectifier (D1-D4).

A transformer needs at least 3 pins (auto-transformer), but usually has 4 or more -- 2 pins for the primary winding, and 2 for the secondary. Your component has 2 pins, so it must be an inductor of some kind.

I suspect that the triac drives a motor, pump, or solenoid. If the track is open, then that could very well be your problem. However, it may be that a shorted motor, pump, or solenoid is the root cause.

It's most definitely a polarised electrolytic. With respect, if you have to ask this question, then you will be facing an uphill battle.

If you can't find an online file hosting service, feel free to email it to me and I'll upload it to my web space. Try to photograph the PCB from both sides.

You appear to be posting from the UK (which explains the 400V cap), so try Maplin.

- Franc Zabkar

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Yeah - having spent this long on it I bet its something trivial!

Thats a fair point - still not too sure why it'd need to be rated at

400v - hmm unless this is something to do with earthing. But yes I can see it and it all makes sense.

My original write-up was poorly written. It has two contacts on the unsooty side and 3 on the sooty side (the side with an unused centre tap) Sorry about the mix-up. I think it is a pulse transformer for driving the motor.

The motor is working fine for the wash cycle so I don't think its that. The PCB track is fine - tested with a multimeter just a bit dirty.

I am certainly no electronics expert you can be sure of that. But I'm not scared of a soldering iron - well, not now I have a decent stand for mine anyway :-)

I'm not trying to aviod the subject but I cleaned the board whilst checking for shorts and the like so the picture would not be that interesting. Last time I took a macro picture it was all blurry - so something else I need to brush up on!

Yup, Maplin was my first port of call but I couldn't find one in their e-catalogue. RS will sell me 5 for =A35 plus postage. But now I come to think of it, I have an old DVD player in the garage....

I'm now thinking that I just jumped to the conclusion that it was the electronic burning smell whereas the problem is probably due to the filter being full of nails. I'll take a look tonight!

Thanks for the followup.

Thanks Franc, for all your help - Bob - I hear you too!

My machine went from bad to worse - it stopped heating the water - which set me about thinking what the real problem was...

It turns out that the capacitor and transformer being slightly cooked was all a red herring :-(

I realised that, becaus ethe motor/drum still all worked that the triac/transformer must still be working. Also, because the controller's LCD screen worked etc etc, that the capacitor (part of the supply to the time/controller) can't be the problem either.

So, I unplugged the machine and sat down to dismantle it.

After I had stripped off the front cover (the big springly thing around the rubber door seal was a surprise as was runnning my finger around the rubber seal itself and catching it on the rather sharp metal frame it covers giving me a nasty cut on my finger) I discovered some really very burned out leads going to the element and the temperature sensor)

Turns out the original real problem with the machine not clicking onto the Rinse and Spin was a well know symptom of, you guessed it, heating circuit problems!

I was so sure it was the capacitor and transformer!

So, its late at night, its a Friday, there are no spares shops for miles - what to do?

Well, I took the burnt mess that was the sensor, ground down the burnt plastic unti lI found the contact and soldered on new wires. I checked its resistence (abou 4.6K ohms) and that its resistence went down when heated (I stuck it in my mouth!) - so that was still working (!!).

The element contact had got rather burned so I cleaned that up too. I checked its resistence - 40 ohms which, I found on the internet, was about right. So I replaced the wrires with some thickish mains cable, put it all back together (I actually wrapped some duck tape around the sensor in the hope of stopping any shorts/arcs from the element contact too)

When I ran it up it all worked - Hoorah! Clean clothes!

I cannot believe how burned the sensror was and still worked but I am not complaining.

Thanks.

Get a new sensor and contact set to have just in case. :)

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