How to Debug a Broken Temperature Controller

How to Debug a Broken Temperature Controller

I have an temperature controller which is not functioning as I would expect, as here. In addition to the pictures, there is a platinum thermometer attached to the thermometer input. I want to repair and find the issue with this controller, so any advice as to the correct approach is highly appreciated. As a fairly clueless mechanical engineer, I will try to explain my current approach.

To test the functionality of this temperature controller, I have plugged a little electric fan into the output of the controller such that at full power, the fan should turn. Meanwhile, I have plugged the controller into the wall socket. I have observed the following: 1. At room temperature, neither the fan nor the display of the controller respond until I elevate the temperature set point to nearly 90 C. At this point, the fan may start to buzz, but it doesnt turn. Meanwhile, the heater display turns to nearly 80. 2. No significant changes in behaviour are observed when placing the temperature probe under cold water. 3. When heating the probe, the exact temperature at which the temperature set point triggers a response changes a little, maybe 3 or 4 degrees lower. Still, the device is unresponsive at temperatures anywhere near the room temperature.

My thinking is that the temperature probe is the most vulnerable part of the device and is likely the part that has gone bad. So, from what I gather, if I short the thermometer input, then I can at least try to isolate the problem.

I assume that if I short the thermometer input, the device would simply output full power at all times.

I had assumed before looking at the circuitry that there would just be two wires across the temperature input, and I could sodder them. However, there are four as seen in the attached picture. Can I simply sodder them together to achieve the same result? Additionally, if the thermometer probe is not the actual issue, what should my approach be from there?

Any other advice and discussion of how this controller works would be greatly appreciated.

Submitted June 15, 2017 at 07:58PM by cnr608
via reddit

How to Debug a Broken Temperature Controller

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