Heater Meter 4.3- Fan always on

Nathan Stock

New member
I had one issues, but during troubleshooting created another.....

Just finished my first build of a heater meter 4.3 w/thermocouple and Pi Zero W. I fired it up and everything appeared to be working ( Fan was not physically connected) I checked it out for a bit and then wired up the fan and connected it. The fan is on as soon as I plug it it, even when the heater meter isn't calling for the fan. I did some searching and attempted to troubleshoot.

- Fan is always on, as soon as the meter is powered the fan turns on running at ~12volts despite the meter calling for 0% fan. Regardless of fan % commanded the fan does not change
- Changed the fan control to voltage to Pulse - not change in fan
- Cleaned the board with Acetone and a tooth brush - no change
- I removed the mainchip on the board and the fan still runs

2nd Issue- I may have fried the LCD/Display Board

In the midst of my troubleshooting, during one the iteration of inspecting and putting it back together I connected the LCD Button board 180 degrees from correct and then powered it up.... Now, the LCD screen dosen't display anyhing, but i Can adjust the contrast to get he black bards up. I can still enable the lid detect and see it in linkmeter and the yellow LED. However, the green and red LED's do not see to be active.

where should i start........
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Bryan Mayland

TVWBB Hall of Fame
There's a bunch of threads about a new build with the blower always running, including one on the first page, so I'll be brief. Trace out the connections from the BLW pin of the microcontroller to the MOSFET to the blower. It is often Q1 damaged in some way or not connected
Blower off voltages: https://heatermeter.com/devel/pcb/hm-4.3/HeaterMeter434Base-BlowerOff.png
Blower on voltages: https://heatermeter.com/devel/pcb/hm-4.3/HeaterMeter434BaseV.png

Flipping the LCD upside down swaps the polarity between 5V and GND, so it is the same as hooking up power directly to the LCD backward. It is very likely the LCD is toast although I'm not sure I've ever done this so I can't say for sure. Sounds like the shift register chip may have survived though if the LEDs are working properly (the green one should also work if this is the case).

Nathan Stock

New member
I changed out the Q1 to ensure that I didn't have any issues with it.

I finally have success! Now I just need to get a new LCD/button board since i ruined that......
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