前文書說道，電路板不是不會壞，但幾率很低。如果經常需要更換，需要研究一下問題所在。
Two examples will be given here.
1, Oven
This oven can't be heated with bake or broil. It uses 240V but for us Chinese who got used to 220V for the first half of live, it is nothing. Just open it and measure.
The light is on, the control is on, so the transformer from 240 to 110 works.
The 240 to heat element goes through several relay (繼電器), one side is energized, the other side is cold.
A simple search on line find a $100 part. Cost 10min to replace it, but get regreted in another 10min.
99% of board problems are due to simple contact issue. This board is no exception. Because of heat, the lead to the relay is floating. Soldering back on in 3 min, and it works as new.
2, AC control board.
AC control board is very simple micro-controller system. So simple it is like toy when comparing to an iPhone. Because of its toy nature, it breaks often.
Let's see its environment, vibration, heat, dust, all pointed to failed solder and loosed screws.
This perticular board cost $100 to replace, but within 2 min by looking at the old board can reveal another hole where ground wire used to be soldered onto. Fix with iron in 2min and the board works just fine.
Conclusion,
Modern components need to pass tons of test for 10+ year warranty, the 6 sigma of their failure is very slim. Look at the board contact first, before replacing them.
I spent well over $200 for this lesson, and hope it can save any handy electrician just that much, each time.
