Drying Oven - Preset Temp Fail

[tmcw]

Re: Drying Oven - Preset Temp Fail

Thanks for the tests...

With the multimeter on continuity/diode mode, I got a readout of 0.127 either way on the fat wires.

When I disconnected one of the fat wires from the circuit, testing the triac, the meter read open.

I'm pretty sure that the temperature readout is correct, at least a couple of degrees Celcius either way.

We actually have 2 other ovens like this in the building, but I'm not sure if they work. I turned one of them on earlier, but the temperature display was a bit wonky, and the temp seemed to be fluctuating, so it may have different issues. I'll test the other one tomorrow.

[redwire]

Re: Drying Oven - Preset Temp Fail

Check if the triac on the big heatsink is shorted between MT1 and MT2. Those are the fat wires on it. That would leave heat on all the time until the safety cutouts trip.
Triac is TAG semiconductor T1513MJ 15A 600V TO-220 isolated, non-sensitive 50mA gate.

Is the temperature readout correct? If it's stuck then I would look at the sensor for water ingress or corrosion etc.

[tmcw]

Here's an unusual one...

This is a Gallenkamp oven, used in a laboratory space, goes up to 220 Celcius, but is usually maintained at about 115 Celcius. Used for drying glassware, molecular sieves, and so on. Oven is in excess of 20 years old.

It heats up fine, there is an orange light on the front that indicates that the unit is heating, and when it reaches the preset temp, the orange light goes out. All good so far.

However, after the preset temp is reached, the temperature continues to rise, power to the heating elements isn't cut off.

Temp continues to increase until the over-temp temp setting is reached, in which case the red light comes on, and the power to the elements is shut off, the over-temp switch is tripped, and the unit cools down.

Pressing in the reset switch allows the unit to heat up the chamber again, and it will again over-temp and switch off, etc.

I've attached a couple of photos of the front panel and electronics inside.

Fuses are ok. Any area in particular to home in on for testing?