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Thread: Pi header plugged in wrong, No LCD with Pi

  1. #11
    TVWBB Wizard Steve_M's Avatar
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    take the atmega chip out and see if there's still 12v at the blower. If so, your blower circuit needs to be fixed.

  2. #12
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    Man I was really hoping it was just the ATMega that was fried, but nope, still 12v at the blower pin when I pulled the chip. I've seen a couple of threads addressing that problem, but I think I'll just replace the whole blower circuit, do you know which parts it would likely be?

  3. #13
    TVWBB Platinum Member Bryan Mayland's Avatar
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    I would say to wait on swapping out blower circuit parts until you've got the new ATmega chip installed. There is no pulldown on the drive MOSFET for the blower so even just ambient charge from the air can charge the gate of the output and cause it to turn on and run the blower at full power. It relies on the microcontroller to actively disable the pin. If you really want to test that you can connect the microcontroller pin labeled BLW to any GND with a small bit of wire (just touch the wire to the pads, no need to solder). The blower should turn off. If it does still run then you do have a problem in the blower circuit as well.

    Another thing to look at is Status -> System Log and Status -> Kernel Log after you try to do an AVR Firmware update (and you get the AVR Fuses ERROR) message. See if there are any new lines at the end of either of those after trying to do the update which would indicate if there's a software problem.
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  4. #14
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    Unhappy

    Quote Originally Posted by Bryan Mayland View Post
    I would say to wait on swapping out blower circuit parts until you've got the new ATmega chip installed. There is no pulldown on the drive MOSFET for the blower so even just ambient charge from the air can charge the gate of the output and cause it to turn on and run the blower at full power. It relies on the microcontroller to actively disable the pin. If you really want to test that you can connect the microcontroller pin labeled BLW to any GND with a small bit of wire (just touch the wire to the pads, no need to solder). The blower should turn off. If it does still run then you do have a problem in the blower circuit as well.

    Another thing to look at is Status -> System Log and Status -> Kernel Log after you try to do an AVR Firmware update (and you get the AVR Fuses ERROR) message. See if there are any new lines at the end of either of those after trying to do the update which would indicate if there's a software problem.
    I jumpered PD3 (pin #5 on the socket) to ground and the blower output was still 12v, so I obviously fried that circuit too. So I might as well order the replacement parts for that. Looks like a diode, capacitor and a couple of mosfets? Any good way to see which one is bad, or what would fail first in this situation?


    Here are my logs for kernel and system log.
    https://pastebin.com/y06Yegjg
    https://pastebin.com/NBXgz82M

  5. #15
    TVWBB Platinum Member Bryan Mayland's Avatar
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    Click to embiggen

    Here's a voltage diagram of what you should see with 0% blower output. You can start at the microcontroller output and work your way back across the traces and maybe see where things are going wrong. Odds are that the first BS170 MOSFET is conducting or the power MOSFET is conducting.

    Driving parts are: BS170, FQU11P06TU, 2.2k resistor, 220u inductor, 1N5819 diode, 47u/25V capacitor. Then the feedback circuit is 64k, 22k, 100k resistor and a 0.1uF capacitor (not included in image). Only the BS170 and FQU11P06TU are likely culprits.
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  6. #16
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    You're working with a HMv4.2.4, right? Here is an image that lays out the blower circuits for that boards, including voltage information for blower on/off states:



    I didn't read the whole thread, but think your troubles started when you plugged things together wrong. If that is the case the components I would suspect are the ATMega and Q1. If I were in your shoes this is how I would proceed.

    First, in the HM config I would set the blower to PULSE mode (not Voltage Mode), this disables the blower feedback circuit. If the blower works properly in Pulse Mode I would suspect something fried in the feedback circuit, perhaps L1. An inductor is difficult to test unless you have a ring tester in your multimeter, most don't, so I would just replace if you suspect it is bad.

    If the blower still doesnt work right in Pulse mode then I would move on to verifying the ATMega is doing what it should. Measure the voltage on Pin5 (blue line) to see if it reads the proper voltage at 0% and 100%, if not then I would pull the ATMega from the socket and insert it back with the leg from Pin 5 not installed in the socket (just bend it outward slightly). Now measure the voltage on the isolated leg of Pin5, if it still does not read the proper voltages then I would re-flash the ATMega and hope that clears up whatever got messed up, if it doesn't behave properly then I would replace the ATMega. If when isolated the voltages on Pin5 are proper then I would re-insert Pin5 and move on to troubleshooting the blower circuit.

    First stop is Q1, center pin should read the same voltages as Pin5 from ATMega. If these voltages are wonky now that Pin5 is inserted back in the socket then I would look for shorts on Q1 or suspect Q1 as bad. If no obvious shorts are found I would remove Q1, verify voltages on Pin5 & center pin of the Q1 socket are proper (the same), then check the voltage on the right pin of Q1, it should be the same as the voltages on the left pin of Q3. With Q1 removed they should both be 0v, and blower should be at full blast. Carefully tap 12V to either right leg of Q1 or left leg of Q3, the blower should shut off. If it does then that verifies Q3 is in working order, if it does not then Q3 may be fried, or there may be a short on the Q3 end of the circuit. If the blower goes off/on when you tap then remove 12V to that leg then I would replace Q1 with a new BS170. If the blower still does not behave I would check that 12V is getting to the right leg of Q3 and also check R14, verify continuity to the next two components from each respective leg of R14 and make sure it is still reading the proper resistance value. If all this checks out it may be time to replace Q3.

    Like I said at the start, I didn't read your entire thread, so if you have already verified any portion of the above then skip over that portion of the troubleshooting routine. The circuit itself is not all that complicated, shouldn't be too tough to fix. If you do end up ordering replacement parts I would suggest you order the entire blower circuit, because the parts are cheap but shipping is more expensive, better to get them all at once rather than ordering twice!

    Hope this was helpful, good luck with your repair!
    Last edited by RalphTrimble; 04-14-2018 at 01:12 PM.
    I created the Roto Damper, RD3, HMv4.2 sliding back case, "air-burner" and the "ping-pong" valve in my quest for delicious "set and forget" BBQ.

  7. #17
    TVWBB Platinum Member Bryan Mayland's Avatar
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    Ah dangit, Ralph didn't even read the whole thread but he gave you a better answer than I did because I completely forgot that you had a 4.2 board and not a 4.3 which is what I drew the diagram for. Not only did he give you the proper diagram but he also added a more complete description than I did.

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  8. #18
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    Thank you both for taking the time to help me, it's really appreciated! And great diagram Ralph, I should be able to test that circuit tonight. My replacement ATMega should be here Monday, and hopefully that fixes the issue with my LCD as well, if not do you think a new shift register is needed, or possibly replacement LCD? I have a spare i2c one laying around but it doesn't look like those are compatible. It's probably cheap enough just to order all of that with the blower circuit parts as well. I'll update after testing everything later.

  9. #19
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    Yes, that sounds reasonable, if LCD is still jacked up with new ATMega then look at the shift register and/or the LCD board itself. Most of the HM parts are real cheap, I would just throw the whole HM parts list into the Mouser cart and then pull off the more pricey items you definitely do not need until the mouser cart total $$ is low enough and order. Shipping will prob be as much as the parts, and spare parts are always good to have around...
    I created the Roto Damper, RD3, HMv4.2 sliding back case, "air-burner" and the "ping-pong" valve in my quest for delicious "set and forget" BBQ.

  10. #20
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    I setup my blower and damper today and am just finishing off some printed parts. When I was hooking everything up I noticed the blower was working just fine. I changed the settings from pulse back to voltage and that worked well too! So it looks like whatever issue I had was involving the ATmega still, it still acts a bit funny. At this point I am able to use the webui to run everything, and hopefully the new ATMega solves my LCD and flashing issues tomorrow. Pretty exciting stuff. Thanks for all your help, I have a much better understanding of the circuit now too!

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