Triac Variable Speed Motor Control (BT136) Repair
The Triac is one of the most common electrical failure parts.
I purchased a package of 5 for $4.50.
These tend to fail not because they're badly made but because manufacturers don't heat sink them properly.
Here's a foot pedal speed control from a Singer sewing machine as an example. Triacs are used extensively in appliances that require speed/voltage control.
Get access to the PC board.
This foot pedal doesn't have any fasteners holding it closed. A small screwdriver can be seen inserted between the foot pedal and the base
Gentle pressure allows the pinion pin to clear its detent hole. If you apply too much pressure you might crack the foot pedal. A two part structural epoxy can fix that if it should happen.
Other devices may require screws or clips be removed to gain access to the triac.
and here's the culprit...
It's unlikely to be any of the other components because the issue is almost always overheating and the triac is usually the most heat sensitive component in the circuit
This guy here.
There are other applications where the board may be different but this is the only part you need to worry about.
Remove the PCboard from its mounting point.
Make a note of which direction it's facing.
Remove it with a small soldering iron and a pair of tweezers or needle-nosed pliers.
It can help to put the edge of the PC board into a vice or use alligator clips to isolate motion of the board so you can use both hands. soldering iron in one hand, tweezers in the other.
Remove any excess solder with braided copper de-soldering wick, or multistrand copper wire and a non-corrosive flux.
At this point you can just put a new triac in and solder it but this problem is caused by poor heat dispersion.
If you don't hardware hack it at this point to work a heat sink in, then you may as well order another triac because it will eventually fail again.
Adding an improvised heat sink:
You can make a decent heat sink with scraps from a disposable pie pan or a piece of hobby metal for detailing automotive and railroad models.
I used JB Weld Steel Epoxy.
It has a longer setting time than the 5 Minute epoxies but it also conducts heat better and doesn't fail when it gets a bit warm.