Bizarre Power Issues


 
T

Tony S

New member
Hello,

So, I've had a few trials and tribulations with my HeaterMeter set up. I tried soldering up my own unit, but was unable to ever get the display to work on the device (Wifi worked fine).

Eventually I just bought a fully soldered HeaterMeter and got that up and running. Everything seemed to be going fine until recently the Raspberry Pi started heating up and stopped working. I realized that I had inadvertently used a 24V power supply instead of a 12V, so I figured I had burned up my Pi. But this is where things get weird.. the Heatermeter still works just fine, I just can't use the Wifi on it. I went ahead and finished the Brisket I was working on and figured I'd troubleshoot later.

So, I swapped my SD card to a new Raspberry Pi and went ahead and bought a TRIAD power supply so I would have the recommended one. The other Raspberry Pi still doesn't work, and I can't get the Heatermeter to power on using the 12V TRIAD power supply. I can get the unit to power on using the 5V power from the Raspberry Pi, but when I do that I just get a black bar of squares on my display. The HeaterMeter still turns on using the 24V, but I presume that isn't good for it. So.. I don't really know where to go from here.. Should I buy another Raspberry pi? Is there a software issue? Do I need a new memory stick? Is it possible that the HeaterMeter isn't ever able to function at 12V again? Is it possible that I got a 12V power supply dud?
 
My first step would be to test the HM power supply circuit. Unplug the rPi and provide a proper 12V input voltage to the HM and check the PS section by section:

Test for 12V at the solder side of the power connector

Test for 12V on the input pin of the OKI 12/5V converter board, and 5V on the output pin

Test for 5V on the input pin of the 3.3v regulator, and 3.3v on the output pin

My first guess was 24V would kill the OKI, but the specs page says max input voltage is 36V. In theory you would think the HM should live through this with the OKI stepping 24v down to 5v just like it does for 12V, so it seems the portions of the HM that run on12V are more likely to be damaged if the OKI does it's job protecting the 5v/3.3V sections with up to 36V supplied.

The blower circuit is the only part that runs on 12V, so I would check out the blower circuit. I posted a pic of that section, looks like if Q1 was damaged it could drain current through R14 to ground and drag down the voltage in your system (making the HM not boot). You could pull Q1 or just lift one leg of R14 to see if this may be the issue. I didn't check max voltage specs on the rest of this stuff, but it looks like most likely to be damaged would be Q1, R14, Q3, D2 and L1.

Blower.JPG

The one HM I fixed that was killed by using the wrong power supply had a blown inductor in the blower circuit, it was an odd one to diagnose...

Good luck!
 
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