My defy f350 freezer most of the times stoops cooling.first we suggested of changing the pc board and it worked for 2weeks.now the alarm light keeps flashing again.as atechnician am stuck now.

NOTE: This
is a multi-solution answer since I don't have all the tech from your question to pinpoint your problem
But the solution is in here generically, if you read and study the solutions very,very carefully.
First I would check cold control. Thats where you turn it off, if your temp is not warm. it can
be defective and not shutting off. If your temp is warm proceed with the following.
I would check the fan in the freezer. Listen to see if it is running
It moves air to the ref from the freezer
Then check to see if FREEZER CONTROL is turned WARMER WHICH MAKES THE REF COLDER AND VICE-VERSA. SEE?
The ref. temp should be about 33-35
The Freezer temp should be 0 to 10 Any thing below these temps is overkill and a waste of elect
The higher the number you turn it up to is the coldest
But is probably a common defrost problem The ice build up
is not being melted by the defrost system.The fan can't blow through the coils into the fridge.
Take out back panel of freezer to check for ice buildup. The coils should be clean.
There are three components to a defrost system- a heater,heater thermostat, and a timer unless you have a defrost electronic card.
Its best handled by a Technician but you could possibly do it by taking your model number to the nearest appliance parts store and asking for the parts. They are mostly located in freezer ,behind back panel on freezer coils.except the card which is usually located in ref The parts store will have info
Also check fan undernearh Ref in the rear
Clean condenser coils underneath
Make sure back cover is on the fridge. Some take them off and throw them away.
make one out of cardboard if its gone, using the holes of the old one.
.I'm including my article on Refrigerator Repair for your help and convenience.;
Please click or copy and paste into browser for Article

http://www.fixya.com/support/r5816737-fix_refrigerator_psychologically
If you need more help go here:

http://www.applianceaid.com/procedures.html

MORE TIPS AND TRICKS:
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STOP PAYING FOR EXPENSIVE WATER FILTERS FOR YOUR REF. DO THIS====
http://www.fixya.com/support/r9962087-stop_paying_high_price_refrigerator
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WATER SPLASHING IN FREEZER AT ICEMAKER
THE FILL TUBE IN BACK OF REFRIGERATOR CAN SLIP
AGAINST THE FILL RESERVOIR CAUSING A PARTIAL BLOCKAGE
OR BECOME CLOGGED WITH ICE.
REMOVE THE ICEMAKER AND INSPECT THE FILL TUBE.
RUN WATER IN TUBE TO ELININATE BLOCKAGE AND CHECK
TEMP IN FREEZER. IF TEMP IS BELOW 0 DEGREES, THATS
OVERKILL AND USUALLY A WASTE OF ELECTRICITY TO KEEP IT THAT COLD, NOT TO MENTION THE FILL TUBE FREEZING UP
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Leo Ponder
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