Cursitor Doom wrote:
This is a 2W resistor. If it's trying to dissipate more than 2W as I
strongly believe, something's definitely wrong. The problem up until now
has been measuring the dissipation, because we can't use I^2*R or
variations thereof because of the highly noisy/irregular waveform. So...
Here's the clever bit:
Measure exactly how long it takes at present for the resistor to reach
say 50'C. I believe it's around 1 minute, but get the exact time. Then
let it cool completely back to the room ambient temperature. Remove from
circuit. Attach to bench power supply and by means of trial and error,
set the voltage across the resistor to raise it's temperature to 50'C in
1 minute (will obviously require several attempts, but no matter). Read
off the voltage level which produces this outcome, then just do V^2/R to
find W and see if it exceeds 2W.
I'll do it first thing tomorrow!

Good test. It would be more straight to plug the right voltage to make it dissipate 2W, for 20 ohm that would be 6,3V and check what temp results in 1 minute. You could use another identical resistor for the test if you have one lying around to avoid unsoldering.