Tin is a very tricky element. It's neighbour in the Periodic Table is germanium, a semiconductor. Beginning at 13.2 degrees C. going down, it starts changing its metallic character to a more crystalline form, almost like powder. At -48 degrees C. it may turn to powder within an hour. All depending on purity and alloy status. Napoleon's army experienced this on the way back from Russia to France in the icy winter of 1812 when the tin buttons of their uniform trousers and jackets deteriorated to dust.
I myself experienced this when my refrigerator freezed all its contents to solid ice a few weeks ago. I swapped the central electronics PC board, but made no points. After some more experimenting, I discovered that the NTC sensor cable, where it was connected to the board, had tinned prongs on the miniature plug. Obviously, after ten years of service at below 10 degrees C., the tin coating on the prongs decided to develop some resistance, adding to the NTC resistance value and causing the microprocessor to run the cooler down as far as possible. I found out by asking lots of people that the manufacturer later had changed the arrangement by soldering the sensor cable to the microprocessor board directly..... Peter Am 03.08.2016 17:32, schrieb jrmitchellj .: > If you follow Gene's suggestion, while you are in the unit, check the > circuit boards for cracked/stressed solder joints. Over the years, heat > cycling will cause joints to crack, especially in areas that generate heat, > like around resistors & transistors. Capacitors can also heat up causing > cracks. As they age, their ESR can rise, causing more heat buildup. > > I have repaired countless items by nothing more than reflowing solder > joints! > > If you are allowing your equipment cabinet to rise to 95 before cooling > starts, the localized rise will be much higher. > > Ray > > --J. Ray Mitchell Jr. > jrmitche...@gmail.com > (818)324-7573 > > --- Diese E-Mail wurde von Avast Antivirus-Software auf Viren geprüft. https://www.avast.com/antivirus ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
