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Franc Zabkar Franc Zabkar is offline
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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
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Please remove one 'i' from my address when replying by email.