Well, that was interesting. Took a bit of work to get the lid off - tamperproof screws!
Pot was working fine. I went round the circuit and found weird voltages. Slow rises in voltage - huh? Components looked OK. So, pulled the circuit board right out so I could get to the solder side. Started up by touching up all the solder joints. What's this? One leg of the output transistor was not soldered! Once done it started working, but not as I expected!
First link is what I expected to see - my homemade PWM controller - short pulse width. (All videos show circuits under load with an 8" DewNot heater strap.)
http://www.youtube.com/watch?v=1ViMA6thhI8
Here is what I get with the Kendrick:-
control at 0%
http://www.youtube.com/watch?v=bja2avB83Kc
control at 50%
http://www.youtube.com/watch?v=zuGuBq5AAiQ
control at 90%, then turned to 100%
http://www.youtube.com/watch?v=5Qg3AgaSf2s
Goodness - 4-6 sec pulse widths! I didn't expect that!
Well now it does work. Woo hoo!