Firstly thanks to Contemporary Maker Rob Schwartz, his blog explain why and how to repair the MOSFET on Ramps 1.4 Board
"When I first got the RAMPS 1.4 board, I wondered why the power MOSFETs for the hotends and the heated bed had no heatsinks. However, after connecting the RAMPS board to the printer, they seemed to work just fine. I soon forgot about the problem entirely... but that was the wrong move."
"Fast-forward to four months in the future. Something strange was happening- the Full Graphic Smart LCD Controller that I set up would dim every time I started to turn on the heated bed."
"Very quickly, I had a much larger problem on my hands- now the heated bed wouldn't heat at all. There was no voltage across the heated bed terminals, and the bed MOSFET refused to show any signs of life or warm up. I believed that I had found my problem- the MOSFET had fried itself to death."
You can find similar topics like 'Ramps 1.4 overheating or shorting?' and MOSFET fried or dead tells that open source hardware Ramps 1.4 or the latest Ramps 1.5 are Not reliable at all. But how could we fix and repair the board?
Keywords: TO-220 heatsinks, MOSFETs, desoldering wire, breakout board
"I came up with a plan. Armed with a small perfboard, some TO-220 heatsinks, and a couple spare MOSFETs, I would build a breakout for these transistors that would allow room for them to cool. 0.1 inch headers have the same hole spacing as the TO-220 package, which is what the MOSFETs on the board are. So I would connect male headers to the RAMPS board, and female headers to the breakout board. A cable harness would connect the two boards."
More than 1,000 words and pictures omitted here, further you can find on Blog Contemporary Maker
"After I got the headers soldered onto the RAMPS 1.4 board, it was time to make the breakout board for the MOSFETs. This would allow them to be able to be heatsinked properly, which helped to make them last longer."
"The last step in the process was to get the cable harnesses set up that connect the RAMPS board and the breakout board."
Reference links:
http://blog.contemporarymaker.com/2015/05/prusa-i3-rework-mosfet-repair-part-1.html
http://blog.contemporarymaker.com/2015/05/prusa-i3-rework-mosfet-repair-part-2.html
