Recently, an unpleasant surprise greeted me when I went through my usual pre-print checks on my printer to make sure there weren't any loose bolts, obvious shorts or loose connections. At first I thought that it was just a bit of dust on the heated bed connection but on closer inspection it was obviously burnt. It hadn't been like that when I started my last print or I would have seen it; in hindsight, that connector must have got ten very hot. At this point I still thought that it was only a small burn and that I could still get a print in but luckily, having time, I didn't risk it and tried to pull the connector out - it was fused in place and took a lot of nerve-wracking work with pliers in the small space around fragile components to remove.
Upon removal it was obvious that this connector had had its day so I cut it off and was thankful that I had some screw terminals on hand which I could replace the under current-rated Molex connectors with, the pins on the board were also covered in charred plastic residue. It was very lucky that I decided to replace the connector because I discovered that the wall in the plug between +12V and ground had been burnt away, so a short could have happened very easily and blown the bed MOSFET which would have been a real pain.
I then soldered in the screw terminals. Desoldering the old Molex pins was a pain with only solderwick available as I could never quite get all the solder out of the holes, so a solder pump/sucker is on my list of things to buy. It was only possible to get it off by pulling the plastic sheathing off the actual pins (which is risky because it puts a lot of stress on the board), so they could be individually pulled out while the solder was molten. Afterwards there was still solder left in the holes to remove, I've found that the best way to tackle this with only solderwick is to put as much solder into the hole as you can so that there is a large bulge of it coming out of the hole, then add lots of liquid or gel flux on top of the little domes and try to wick the solder out with the solderwick. I found that you have to leave the wick and iron there for at least 7 seconds to be sure of clearing the hole, some holes took me a few tries.
The screw terminals that I used were very hard to find, it turns out that 2.54 mm pitch (do not get 5 mm or 5.08 mm pitch by accident as these are by far more common) screw terminals are hard to come by and that 4 pin ones are even rarer than 2 or 3 pin ones. I couldn't find them on element 14 or similar suppliers and a search through eBay's own search engine turned up nothing, but Google directed me to these ones on eBay with the exact same search query I put into eBay's search engine. eBay's search engine is broken. So far this is the only source for 2.54 mm pitch 4 pin screw terminals that I have come across. They appear to be rated (according to some writing on them, for 6A up to 150V per pin with RU certification though I would take this with a pinch of salt given the lack of branding and the supply source). Fingers crossed that these will work for me. Also of interest, nophead has his own Sanguinololu modifications which I think would leave a lot more margin for safely carrying the bed's current but a ring terminal is needed and the modification results in it being a bit harder to get a heat sink on the MOSFET.
