"amcwill417" bravely wrote to "All" (05 Nov 05 22:59:36)
--- on the heady topic of " Problem for 15 year old 32" TV"

am From: "amcwill417"
am Xref: core-easynews sci.electronics.repair:347676

am A HAPPY EVENT!
am This Saturday evening I opened up the TV and removed one of the
am circuit boards for inspection and resoldered some suspicious looking
am solder joints. Then I replaced it and turned on the set and nothing
am changed - set still did not work. Then I turned on the TV and pushed
am down on the HV transformer with a long stick so as to distort the
am circuit board it is on and WHALA that did the trick. The set now works
am fine!!! I guess I will have to resolder components on this board
am sometime soon since I suppose there must be a loose solder joint
am somewhere. I do not understand why this Sony TV has had so many
am defective solder joints. It is a wonder that it has worked at all
am over these many years.


Alex,

Heat around power devices will cause thermal expansion and then
contraction when cooled. Eventually the solder becomes metal fatigued
and brittle. This increases resistivity of the solder and the joint
can even burn up in extreme cases.

Case in point, when replacing power transistors in audio amplifiers I
always used to leave a little semi-circular bend to the leads so that
as the devices heated up the bend would take up the slack and wouldn't
pull when cooled again.

A*s*i*m*o*v

.... Wasted power is current squared times the resistance.