On 02/02/2015 6:23 AM, Rossano Gobbi wrote:
> Hello people,
>
> I have this tumble dryer that gives no sign of life
>   anymore. I opened it up and sought for any evident sign of failure on
> the main board but found none.
>
> A picture of the board, just to give an idea: http://oi60.tinypic.com/x40=
mbq.jpg
>
> I
>   have some electronics background but never worked in the field and
> never practised (beside PIC programming...) so I was wondering if anyone
>   could give some repairing advice/general guideline when debugging this
> kind of circuits.
>
> Kind regards
> Rossano
>
>   		 	   	=09
Hi Rossano,

I have had a quick look at the picture, and suggest, that you check each=20
relay.  One or more than one may be used to cut power.

Relay contacts can often test good when tested with a multimeter for=20
good continuity but in fact can still fail under load, and it may even=20
be required to remove each relay from the board and power them up=20
individually, and using a low ohms meter test the contacts resistance,=20
over many ON/OFF cycles.

Simply hearing the relay click isn't a good test, you also need to check=20
the contact resistance as well.

I generally do this at the work bench, as many relays are either 12V or=20
24V coils.

I have fixed many boards with problem relays out in the field, over the=20
years. Sometimes the fault is easy and sometimes it's hidden.

This goes for washing machines, office equipment, and others as well.

There may also be poor solder joints on the input connectors to the board.

Something else to try is carefully with the board powered, simply=20
measure the voltages that are across the electrolytic capacitors, with=20
the unit in the ON state. Then look at the electrolytic cap's and see=20
what voltage rating they are.

If there are no signs of life, then, I'd suspect, at least not to rule=20
out a faulty relay contact, and/or connector.

Also do some un-powered investigation, by following the cable signal=20
from the power plug and into the circuit with a multimeter, test each=20
cable to the board and in through the connectors.

There may also be some capacitors in the switch mode power supply that=20
have failed, causing the supply to fail to start-up, and hence the board=20
would look dead.

Interesting...

Good luck.


Peter

--=20
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