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System fan control
The system fan is quite noisy and only needed when temperature is above a certain value. The improved firmware can use the cold junction sensor to turn the fan on and off.
This utilizes the (previously unused)
ADO testpoint that is connected to
GPIO0.25 to drive a N-channel mosfet or NPN transistor to control the fan.
The pin closest to the edge of the board is
VDC, the other pin is
For example: 2N7000 (N-channel mosfet).
Gate connects directly to
ADO testpoint, source to
GND, connect drain to former
GND wire from fan.
BC547B (bipolar NPN transistor).
ADO with a 4k7 resistor to BC547
base pin. Break the ground lead and connect it to
collector. Connect the emitter to
Example of this mod in picture above.
Although this mod appears to be for a T-962A with the external SSR, it could also be applied to a T-962 (smaller version of the oven). In the T-962, the heater control is done via a triac mounted on the PCB. This triac is very marginally designed and gets fairly hot during operation. Its heatsink is fairly small and there is no heatsink grease. In addition, the optoisolator driving the triac only has about 20% of the worst-case drive needed to ensure the triac turns on properly.
Reducing the air flow over this triac would make the triac run even hotter, so beware of that if you do this mod on the T-962. If you install a more silent fan instead, you're looking for a 12V fan with max 40x40x20mm (or 40x40x15mm if you want to install the 4th screw.)