Overheating connectors

[chris_leyson]

Recently had my central heating boiler replaced with something that isn't a complete pile of shit like the old one made by an Italian company, all the plumbers I've talked to agree on this. Over 15 years it's needed three flue fans, three water pumps, two diverter valves and another set of elbow couplings with mixed imperial and metric threads  maybe I should add "and a partridge in a pear tree" as it's getting near Christmas. In spares it's probably cost me twice what the pile of shit boiler cost in the first place.
About 5 years ago it stopped completely, no lights, maybe it's blown a fuse ? Take it apart and have a look. PCB had turned into the equivalent of burnt toast around the fuse holder and the power connector where the live is connected and the crimp terminal had got so hot that it has soldered itself to the pin on the PCB connector so you can't remove the connector, right hand side in the photo. Clean it up and replace the fuse holder, get another 5 years life out of a piece of shit. Plumber told me he's seen this lots of times but I didn't bother to ask him if it was in the same Italian manufactured boiler or just in general, fuse is 1.6A slow blow and I'm guessing the RMS current is probably a lot less than 1A so there have must been a very large voltage drop across either across the fuse holder terminals or the PCB connector to generate enough heat to turn FR4 into toast, Ohms law. A stalled induction motor in the flue fan (bearings ceased, mild steel motor shaft wears down and rotor doesn't go around) or a burnt out water pump ? Don't think so, it would have blown the fuse if anything was drawing too much current. I think it's got to be a connector plating issue to generate so much heat. Glad to have got rid of the pile of shit. BTW Can't see any UL markings on the PCB either.

[stj]

a pcb will burn like that from a fractured solder joint.

i used to work in the laundry industry with similar controllers and we routinely resoldered and recapped all controllers every couple of years.

[Jeff_Birt]

I have seen several different types of equipment with similar problems. Generally it is caused by poor board design. When you have a connector that handles high currents, has a fair amount of mass and is subject to vibration you are asking for trouble. The pins of the fuse holder are flat and thick but they used large round holes. That leaves you with just a large blob of solder to bridge the gap a poor mechanical connection leads to a poor electrical connection. A lot of times when they use a large round pad like that the hole is so large you are left with too little copper making a mechanically and electrically poor connection. Look at the other joints for the connector beside the fuse holder, the connector pins were not heated enough, the solder did not wet out (round edges) this is a cold/dry joint and it will fail.