Hi Rich, I don't recall seeing a set screw to adjust the frequency for the blinking light, and the No. 193 instruction sheet that came with the Tower does not mention it, either. You are fortunate to own two that have that feature.
Hi Dan, I'll give the unit a good cleaning, and see if accumulated dirt between the bimetallic strip and the thermostatic switch is the culprit. As you say, there aren't too many parts under the hood with this particular accessory, so only a few things can be checked.
Thank you, both for your suggestions. Urbie