Blower circuit troubleshooting


 
J

John Bostwick

TVWBB Wizard
I recently received a heatermeter, that looks like it got wet, it ruined the Pi, and I had to replace the LCD. It works, except the blower and the servo.

Here is what I see.

Plug in the heatermeter and nothing wrong so far. Blower is 0%
Manually change blower to 10g+ and the mosfet begins to get very hot and when it get above 60% it starts to melt solder.

Before I remove the mosfet, and replace it with a new one, I just what to make sure thats the issue. I think the output is screwed up and its just converting everything to heat. I will probably replace all the blower components just to be on the safe side, anyways.

John
 
John Bostwick said:
Manually change blower to 10g+...
Click to expand...
10g+!? That's too many g, man!

I wouldn't think it is the MOSFET but rather that something further down the line is shorted. Measure the resistance on the blower output (between 12V and GND) with everything off and make sure it reads as completely open in one direction. A diode test if you have that function could be more useful, open one direction, like 0.3V (I think) in the other direction.
 
I agree, if the mosfet were toast it would most likely get smoking hot no matter what the HM it was telling it to do, I suspect something down stream is drawing excess current. Does it get hot with no load (no blower) connected? If so, check for shorts at the CAT5 jack and in the feedback circuit, which is across the blower output like a load.
 
Correct, it wasn't the mosfet, and I did not find a short. In the meantime I just redid the board with a new one and will have more time to play with it to find the issue.

John
 
When you back around to troubleshooting I would check the blower, D2, C12, R22, C7, look for shorts/low resistance and soldering issues on those components.
 
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