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Thread: Servo troubleshoot

  1. #1
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    Servo troubleshoot

    Hey guys,

    I just made a Heatermeter 4.3! Everything is working except the servo.. I was hoping some of you could give me a hand troubleshooting my issue.

    Raspberry Pi 3 B
    Power Supply (Same brand as suggested) 2A
    Servo MG90D
    Blower 15cfm (works properly)

    I know the MG90D is working because when I touched the yellow cable with my multimeter it was moving randomly.

    I read a few threads and saw that the Q5 BS170 could be the issue so I replaced it. No dice. Also someone had a bent pin on the ATMEGA. Mine looks fine.

    What other component could be affecting the servo? I guess I could replace the 1k resistor next to the CAT5 jack, but I tested it with a multimeter and it seems to be working fine.

    I don't really know how to test the circuit with a Multimeter, how do I check the servo signal and 5v? I guess ground is working fine because the blower use it.

    also, I had a few problems connecting the BS170 so I replaced them all with new ones I bought from a store near my place. I guess all BS170 are the same, but they didn't have the same things written on them... They didn't have the "F"... not sure if this makes any difference.

    What other pieces I could test/replace/resolder that could help my situation?

    Thanks
    Last edited by SPDecoste; 03-14-2019 at 03:36 AM.

  2. #2
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    Have you tried placing a capacitor across the servo leads? I read that it helps sometimes with eradict behavior. Here is a link where they mention it. I would also wait to see if others chime in regarding if the mg90d is compatible.

    https://tvwbb.com/showthread.php?716...vo%20capacitor

  3. #3
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    Quote Originally Posted by GregC View Post
    Have you tried placing a capacitor across the servo leads? I read that it helps sometimes with eradict behavior. Here is a link where they mention it. I would also wait to see if others chime in regarding if the mg90d is compatible.

    https://tvwbb.com/showthread.php?716...vo%20capacitor
    Thanks for the tip. I just got a mg90s so I'll try this tonight

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    I tried with a MG90s, not working. I tried changing the 1k resistor... nothing

    My board might be damaged from my poor soldering skills... When I changed the BS170 I might have damaged the circuit around the joints. I'll keep on looking.

  5. #5
    TVWBB Honor Circle Bryan Mayland's Avatar
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    What's it doing, is it going to weird positions and jittering all around, or is it just totally dead and not moving at all (even if you move it to a different position before powering on)? The first is usually solved by the capacitor. Have you tried measuring the voltage between "Servo" and "GND" at the output jack? It's a 5V PWM signal so depending on your multimeter it might display differently, but on mine it shows ~0.38V at 0% output and ~0.70V at 100% output.
    I'm that HeaterMeter guy what ruins everybody's free time.

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    Quote Originally Posted by Bryan Mayland View Post
    What's it doing, is it going to weird positions and jittering all around, or is it just totally dead and not moving at all (even if you move it to a different position before powering on)? The first is usually solved by the capacitor. Have you tried measuring the voltage between "Servo" and "GND" at the output jack? It's a 5V PWM signal so depending on your multimeter it might display differently, but on mine it shows ~0.38V at 0% output and ~0.70V at 100% output.
    Not moving at all.

    I get ~4.96V on the HM board from GND to Servo.

    I changed the Q5 bs170 twice...

    I get ~4.86V from GND to Servo on the cat5 jack at the end of the servo. Is that correct?

  7. #7
    TVWBB Honor Circle Bryan Mayland's Avatar
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    That does not sound right, unless your multimeter is only reading the peak voltage and not the average voltage. You can check that by measuring the servo output from the microcontroller on the pin labeled SVO (or on the gate pin of Q5, closest to the microcontroller). If it reads 3.3V I suppose your multimeter is reading only peak voltage so those numbers seem right. If it reads a low voltage, like 0.45V at 100% then that's right and something is feeding 5V into your servo output. If that is the case then maybe check between the +5V and SERVO pin on the output with no power connected and you should see a resistance of about 1Mohm (no servo connected).
    I'm that HeaterMeter guy what ruins everybody's free time.

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    Quote Originally Posted by Bryan Mayland View Post
    That does not sound right, unless your multimeter is only reading the peak voltage and not the average voltage. You can check that by measuring the servo output from the microcontroller on the pin labeled SVO (or on the gate pin of Q5, closest to the microcontroller). If it reads 3.3V I suppose your multimeter is reading only peak voltage so those numbers seem right. If it reads a low voltage, like 0.45V at 100% then that's right and something is feeding 5V into your servo output. If that is the case then maybe check between the +5V and SERVO pin on the output with no power connected and you should see a resistance of about 1Mohm (no servo connected).
    Thanks for taking the time to help me out!

    GND and Gate Pin of Q5 gives me 5.16V @ 0% and 5.20V @ 100%.

    I went through all the installation over and I have no idea where to look at now.

    The only thing I could think of is that I had to buy new bs170 because I messed up the first time installing them and the one I bought are not labeled exactly the same as the one that came with the kit.

    The one I bought says:

    CAL
    B$170
    M9705

    I don't know much so I asked the guy if there was different type of BS170, he said no and gave me this... https://abra-electronics.com/ics-sem...60v-bs170.html

    I'll try to find the exact same one as you.
    Last edited by SPDecoste; 03-15-2019 at 03:47 PM.

  9. #9
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    What are your Servo Pulse Duration settings in the HM config? Maybe the issue is there?
    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. #10
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    Quote Originally Posted by RalphTrimble View Post
    What are your Servo Pulse Duration settings in the HM config? Maybe the issue is there?
    Everything is default. Should I change something?


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