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Thread: HM 4.3 fan and servo problem

  1. #1
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    HM 4.3 fan and servo problem

    Hi all,


    I've put together a wonderful HM 4.3 and would like to hook it up to a RD3.

    Whilst the HM is booting succesfully and i have no errors, the fan keeps spinning. In manual mode, even at 0% setting, it is still running. Anything over 0% will give it near full throttle, all the way up to 100% (There is no gradual increment in RPM).
    As for the servo, it jitters a bit, seemingly unrelated to the fan setting. Then it stops, there is no movement whatsoever.

    This is wat I did to troubleshoot so far:

    • Reflow all relevant connections
    • Change out Power Supply to a 12V 3A stabilized PS
    • Check wiring and voltages, the pinout corresponds to the wiring both at board level and final connector
    • Voltages are nicely in line, but the 12V is not dropping when fan setting is low
    • Changed out servo and tested is on another Arduino sketch - works fine there
    • All components are soldered in and checked for continuity to the board


    If I hook up the servo only - it is working
    If I hook up fan only, still no increment in RPM with manual mode

    I'm thinking there is something wrong in the 12V driver circuit (or whatchemecollit) and it's most likely a simple error?

    I'm thinking I might have swapped a thing or two or have a bad component, but my knowledge is lacking in the electrical part.

    Any thoughts or input is much appreciated. photo of the board is here:


    upload image


    upload image

    Thanks!
    Last edited by JonathanNL; 06-23-2019 at 04:01 AM.

  2. #2
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    First thing I would do is go to the HM config and set the fan to PULSE mode, this eliminates the feedback circuit which regulates the blower speed in voltage mode. Does your blower increment speed properly now? If so, then you have an issue with the feedback circuit, if not then you have a larger issue.
    Here is the part of the schematic showing the blower circuit with some notes, I would check these components next:


    Here is pic showing a few of the components and their connections on the HMv4.3 board:


    Here is a pic showing the entire blower circuit on the HMv4.2 board with more notes and voltage references:


    I would check the voltage on those two transistors where I have referenced the OFF/FULL voltages for the blower (leave your HM in PULSE mode for testing, set blower to Min=0 Max=100 Startup Max=100 and your voltages should match the chart). Follow the voltages to the malfunction.

    PS Make sure you have not bridged the solder on the large MOSFET, I've seen that happen a time or two... and looking at your pictures, hard to see but make sure the left leg on the BS170 (the one that goes to the bigger MOSFET) isn't shorted to the ground plane that surrounds it, that would make the blower run full blast all the time...

    Good Luck!
    Last edited by RalphTrimble; 06-23-2019 at 04:26 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.

  3. #3
    TVWBB Honor Circle Bryan Mayland's Avatar
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    Thanks for posting, Ralph. When I saw this yesterday I resolved there there needs to be a wiki article for this since it comes up every month but I ran out of time to work on it yesterday. Will be forthcoming with high priority though.
    I'm that HeaterMeter guy what ruins everybody's free time.

  4. #4
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    Thanks both.

    I followed the steps and can reproduce all but the Q1 to Mosfet, which sits at around 8V when blower is off. That same 8V is then coming out of the blower output at 0% setting.
    When set to pulse mode all is well in terms of incremental RPM but still no stand still at 0%.

    Thinking Q1 is shot.

  5. #5
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    Could be a couple things....
    First, I have helped others who had a bad flash of the AVR that made the blower act weird, so you might flash the AVR again to be sure it isn't software related.
    If the output of Q1 is maxing out at 8v (should be 12v) check the +12v side of R14 (refer the schematic above), is it showing 8v or 12v there? Check the value of R14, is it 2.2K?
    It could well be that Q1 is dead due to overheating during soldering or whatever, if you don't have a spare you can steal the BS170 from the buzzer circuit.
    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.

  6. #6
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    Alright, finally had time to get me another BS170. Got two, just in case. Turns out I had a bad Q1 and a bum servo.

    All seems to be working now, tonight I'll have a test cook to see how the settings are.

    Thanks to Bryan and Ralph for your design and your customer support. Now, to get cooking...

  7. #7
    TVWBB Honor Circle Bryan Mayland's Avatar
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    Wow it is really surprising how many builds have the same problem and it comes down to Q1. Did it look damaged at all from the outside? I wonder what causes it otherwise. The only thing I can think is that because it is the closest one to the edge it has the highest potential to be damaged when handling, or perhaps it is the first one that goes in so it is installed with the least amount of experience? Just thinking out loud for possible future revisions that are more bullet-proof.

    Nice work troubleshooting and getting it up and running!
    I'm that HeaterMeter guy what ruins everybody's free time.

  8. #8
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    To be fair, not sure what caused it. I installed it without a hitch and it looked fine coming out. I am almost sure I did not overheat it when it went it, I took great care that would not happen, equipment-wise and experience. Perhaps it was damaged with the housing, not sure.

    I lack the knowledge to actually suggest a workaround or alternative, but I did read about Q1 being an issue before.

    All in all, I'm just happy I could serve up a good surf and turf tonight - with more to come tomorrow. It held temperature very well and with just a bit of fine tuning left, I'm looking at a great grilling summer!

  9. #9
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    I have experienced the Q1 issue and I caused the problem. If your not careful when installing the boards into the case, Q1 can be twisted and even destroyed by forcing boards into a tight tolerance case. I am sure lots of the Q1 issues are them same as I experienced.

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