I think I smoked my board


 
H

Hans

New member
Hi all,

Appreciate all and any of your help on this. I just finished assembling my HM 4.2 board (pi A+ version), some photos below. My pi works fine disconnected from the PCB, however once connected to the PCB it didn't power on anymore.
Then I tried (without the pi connected) to power the board using a 12 V adapter and directly I noticed some smoke coming from the board. I quickly disconnected the power supply without being able to see what component was smoking.

I am a bit clueless on what to do now. I would like to find the faulty component(s)/mistake(s) in my board but it seems difficult to do without being able to power the board.

Anyone of you any ideas?

Thanks a lot!
Hans

Photos: https://imgur.com/a/RGbVllD
 
Hrm, you're right, that's going to be tough to diagnose if you can't power the board at all. I'm looking at your photos and the #1 thing I see that's not right is that there's a thermistor jack installed but you've also got a thermocouple amp. I'm not sure this would cause a problem unless a probe is inserted though. Maybe start by removing the jack on the pit probe?

The only troubleshooting I can think of is that the 5V regulator has a over-current protection, so it should shut down if you try to pull 2A from it, but that is 10W which is plenty enough to make smoke come out of any component on the board apart from the blower circuit. I'd start with multimeter and measure resistance between various points to ground, like 12V to GND, 5V to GND, 3.3V to GND. They should all read high values (not less than 100 ohms anywhere). That should at least be able to narrow down on which area we can start to look. Maybe also check all the TO-92 parts (the 3.3V regulator MCP-1700, and the BS170 MOSFETs) to make sure the regulator and a MOSFET aren't swapped.
 
Bryan Mayland said:
Hrm, you're right, that's going to be tough to diagnose if you can't power the board at all. I'm looking at your photos and the #1 thing I see that's not right is that there's a thermistor jack installed but you've also got a thermocouple amp. I'm not sure this would cause a problem unless a probe is inserted though. Maybe start by removing the jack on the pit probe?

The only troubleshooting I can think of is that the 5V regulator has a over-current protection, so it should shut down if you try to pull 2A from it, but that is 10W which is plenty enough to make smoke come out of any component on the board apart from the blower circuit. I'd start with multimeter and measure resistance between various points to ground, like 12V to GND, 5V to GND, 3.3V to GND. They should all read high values (not less than 100 ohms anywhere). That should at least be able to narrow down on which area we can start to look. Maybe also check all the TO-92 parts (the 3.3V regulator MCP-1700, and the BS170 MOSFETs) to make sure the regulator and a MOSFET aren't swapped.
Click to expand...

Thanks a million for your reply Brian, really appreciate that. After removing the jack on the pit probe I got some life again! So now when I connect the pi and power it through the pi's microUSB the LCD background lights up and turning the potentiometer I can see a line of black squares. I believe I saw some thread about it so I will now start looking for that.

Btw, I also checked the resistances GND to 12,5, 3.3 V as you suggested and they were all fine, TO-92 parts were also correct.

Thanks again,
Hans
 
If you are now getting black squares on the display that sounds like you are in the fresh build state, not having the AVR programmed yet. At first boot the rpi should see the blank avr and flash the HM firmware to it, it should then show NO PIT PROBE on the HM display (when contrast is adjusted properly).

Hard to say what state all your stuff is in after the rough startup you describe, it seems you now have proper voltages so that's a start! Maybe the smoke came from the thermocouple amp due to the wrong jack being installed? I never analysed the circuit for a scenario like that, but if you have proper voltages and no more smoke or heat on the board I would move forward on the usual path for a fresh build.

The path forward is to have a working install of the HM software on the rPi, boot the HM with the rPi attached and let it flash your AVR... from there you should have a working HM. It can be hard to tell what is happening, and not happening, just looking at the boards and LCD with black boxes. What version rPi do you have? If it's an older version the wired LAN and HDMI ports on the board can be helpful. The wired LAN makes connecting to the HM a no brainer (as opposed to getting WIFI connected) and plugging the HDMI into a monitor will show you if the HM software is loading on the rPi. If you know the software is loading on the rPi then you can proceed to investigate why it is not communicating with the ATMega on the HM board.
 
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PS
Make sure the rPi isn't hitting the buzzer legs when installed, they are quite exposed there the way it is mounted....
 
Quick update: after burning the latest release on a SD card I was left with a working and totally awesome board! A thing to mention is that the TP-LINK TL-WN823N adapter sold in the EU comes with rtl8192eu instead of rtl8192cu. I bought an Edimax adapter and that one worked flawlessly.

Thank you Brian and Ralph for your help, you guys are fantastic.
 
Oh hey that is good information, I will update the wiki to warn our EU friends. Good to hear you're up and running too!
 
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