Yes, I checked the sensor at the connector that plugs into the control board and the resistance is correct.
There is no keypad/panel at the front just below the cooktop. The button panel and the computer board are a combined unit mounted on the back panel of the stove between the cooktop element controls. The unit is a Robertshaw K0611CA manufactured in 1997.
As I tried to explain in my original email, the control board appears to function correctly. The clock works, the timer works, "Bake" comes on as expected and the element starts to heat up, the bake temperature can be adjusted as required with the up/down buttons, "Broil" comes on as expected and the element heats up.
The problem is that something is causing the control board to think that the desired temperature has been reached when, in fact, it has not. The oven starts to heat up normally and the pre-heat timer counts down normally, all exactly the same as before the problem arose. Then, and this is the new situation, the oven element relay clicks off after 25 seconds but the pre-heat timer continues to count down as if all is well. After about another minute the oven element relay clicks on again for 25 seconds and then clicks off again. The cycle continues over and over: 25 seconds on, one minute off. The oven temperature never gets much above 200 degrees F (I used a digital meat thermometer with the probe sitting on the oven rack inside the oven to track the temperature).
I don't know what else to tell you about the problem. It arose without any apparent cause. We cooked a turkey for Christmas without any problems although, and maybe in hindsight this is important, it was done a lot sooner than expected. The following week, we tried to bake some falafel balls and couldn't.
Anyway, I hope something in the preceeding information is helpful to figuring this out.
If you can't answer this one then please say so and I won't pursue it any further.
Thanks for your time and effort.