Cheap-o regulator rectifier

Given how hard it is to get a regulator rectifier for an old bike (I'm probably going to be waiting 6 more weeks), I thought I'd add a little more to my analysis yesterday (see here) of the failure.

The problem was clearly thermal run-away and (not yet) that of the thermal paste (which isn't used anything like properly). So lets start with what the regulator rectifier looked like on extraction from the bike.

The bulge and the spatters of metal (yes, metal) indicate high temperatures (to melt the metal).

So I cut the arse of it off and chiselled it out.

Which shows that there was still some thermal paste, but also that there was not a good physical connection to the metal of the heat sink (because its quite rough looking, ideally it should be polished smooth. So that's manufacturing failure #1

Next we flip that black box over and see that its easy to split (its already fractured)

and we can see the guts ... of course the board is burned down to glass fibers in places. Not only is the heat escape pathway interesting, but what the fcuk are these little chunks of white rock doing in here?

you can see that the not only are the components toast, but we can see the legs of the coponents are totally gone too

This would explain the tiny spatters of molten metal above.

Lastly the thing stinks, probably due to the boiling of the organic solvents used in the (copiously applied) thermal paste.

On this point I'm going to say that cheap thermal paste that uses organic solvents, when applied like a kids use of toothpaste is a recipe for disaster longer term. This is because any significant heat (say, over 50C) is likely to see the loss of this material over time; weakening the effectiveness of the transfer of heat from components to outer case.

So if I was you, as well as making sure it stays cooler (as I examined in the previous post)  I'd be replacing these things pre-preemptively after every few tens of thousand hours (roughly equal to kilometers) or per few years on bikes that don't get used much. Especially if you use your bike on hot days (like Australia, California or other hot dry places).

HTH