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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

Bosch washing machine burned out capacitor and transformer...



 
 
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  #1  
Old November 10th 08, 08:42 PM posted to sci.electronics.repair
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Posts: 6
Default Bosch washing machine burned out capacitor and transformer...

My Bosch Washing machine isn’t working very well – it won’t move to
the rinse part of any program.

Taking it apart, it looks like it has burned out a 470uF Capacitor
(400v) and maybe a small transformer (Marked “KA 19/04” and 063.783 )

The capacitor seems to have stained the circuit board and the
transformer seems to be covered in soot

Which would explain the burning smell :-)

Now, I think this transformer is the low powered supply to power the
brain (and the LCD) which is still working (!!)

Am I right about what this transformer is doing?
Does it sound like it needs replacing?
If I replaced it, might it fix the problem?
Might I just need to change the capacitor?

If I need to replace the transformer, can someone help me identify a
replacement as google seems to struggle with it.

Its about 15mm by 10mm and stands about 12mm off the board.
It seems to have 2 contacts on one side and a center tap on the other
– though this is not actually connected to anything.

Thanks
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  #2  
Old November 11th 08, 08:10 PM posted to sci.electronics.repair
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Posts: 1,569
Default Bosch washing machine burned out capacitor and transformer...

On Mon, 10 Nov 2008 11:42:35 -0800 (PST), put finger to
keyboard and composed:

My Bosch Washing machine isn’t working very well – it won’t move to
the rinse part of any program.


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

Taking it apart, it looks like it has burned out a 470uF Capacitor
(400v) and maybe a small transformer (Marked “KA 19/04” and 063.783 )

The capacitor seems to have stained the circuit board and the
transformer seems to be covered in soot

Which would explain the burning smell :-)

Now, I think this transformer is the low powered supply to power the
brain (and the LCD) which is still working (!!)


Am I right about what this transformer is doing?
Does it sound like it needs replacing?
If I replaced it, might it fix the problem?
Might I just need to change the capacitor?


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.

If I need to replace the transformer, can someone help me identify a
replacement as google seems to struggle with it.

Its about 15mm by 10mm and stands about 12mm off the board.
It seems to have 2 contacts on one side and a center tap on the other
– though this is not actually connected to anything.

Thanks


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
--
Please remove one 'i' from my address when replying by email.
  #3  
Old November 11th 08, 10:07 PM posted to sci.electronics.repair
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Posts: 6
Default Bosch washing machine burned out capacitor and transformer...

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? :-)
  #4  
Old November 12th 08, 04:31 AM posted to sci.electronics.repair
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Posts: 3,241
Default Bosch washing machine burned out capacitor and transformer...

On Nov 10, 1:42*pm, wrote:
My Bosch Washing machine isn’t working very well – it won’t move to
the rinse part of any program.

Taking it apart, it looks like it has burned out a 470uF Capacitor
(400v) and maybe a small transformer (Marked “KA 19/04” and 063.783 )

The capacitor seems to have stained the circuit board and the
transformer seems to be covered in soot

Which would explain the burning smell :-)

Now, I think this transformer is the low powered supply to power the
brain (and the LCD) which is still working (!!)

Am I right about what this transformer is doing?
* *Does it sound like it needs replacing?
* *If I replaced it, might it fix the problem?
Might I just need to change the capacitor?

If I need to replace the transformer, can someone help me identify a
replacement as google seems to struggle with it.

Its about 15mm by 10mm and stands about 12mm off the board.
It seems to have 2 contacts on one side and a center tap on the other
– though this is not actually connected to anything.

Thanks


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
  #5  
Old November 12th 08, 07:35 AM posted to sci.electronics.repair
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Posts: 1,569
Default Bosch washing machine burned out capacitor and transformer...

On Tue, 11 Nov 2008 13:07:33 -0800 (PST), put finger to
keyboard and composed:

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!


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

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)


This is a switchmode PSU out of a cheap DVD player:
http://www.users.on.net/~fzabkar/DVD.../G1928_PSU.gif

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

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.


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.

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 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.

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?


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

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.


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.

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


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

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
  #6  
Old November 12th 08, 10:52 AM posted to sci.electronics.repair
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Posts: 6
Default Bosch washing machine burned out capacitor and transformer...

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

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

This is a switchmode PSU out of a cheap DVD player:http://www.users.on.net/~fzabkar/DVD.../G1928_PSU.gif
Notice the 22uF, 400V capacitor (E1) at the bridge rectifier (D1-D4).


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.

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.


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.

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.


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.

Is this capcacitor likely to be a non-polarised version or just a
plain electrolytic?


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


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 :-)

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.


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!

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


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


Yup, Maplin was my first port of call but I couldn't find one in their
e-catalogue.
RS will sell me 5 for £5 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.
  #7  
Old November 16th 08, 04:40 PM posted to sci.electronics.repair
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Posts: 6
Default Bosch washing machine burned out capacitor and transformer...

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.
  #8  
Old November 17th 08, 01:24 AM posted to sci.electronics.repair
external usenet poster
 
Posts: 64
Default Bosch washing machine burned out capacitor and transformer...

writes:

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.


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

--
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