Results 1 to 7 of 7

Thread: Heatermeter thermocouple temp linear drop

  1. #1
    New Member
    Join Date
    Oct 2016
    Location
    Oklahoma
    Posts
    5

    Heatermeter thermocouple temp linear drop

    In the middle of our move unfortunately it looks like the heatermeter may have been dropped as one of the corners is chipped. Even after this it worked fine for at least one rib smoke, but the last rib smoke I noticed that at times the temperature would drop at a linear rate according to the heater meter while the actual smoker was showing the temp steady or rising. I resorted back to the using the smoker's thermometer (the horror) and the ribs came out a bit more well done than I was hoping.

    When moving the heatermeter out of the way I noticed that the temperature would respond depending on where I placed it, the temp would jump up and then drop in a linear fashion. Then ever so often it would drop significantly, and then back up. I also noticed that the thermocouple temp would jump if I tapped the heatermeter.

    So I thought this was due to the thermocouple, so I ordered a few. And unfortunately with a brand new thermocouple it still seems to be happening. Does anyone have any theories or points I should check in the thermocouple circuit that could help narrow this down?

    I have some experience with soldering and a multimeter, but would appreciate some help in narrowing down where I should start looking.

    Thanks in advance.

  2. #2
    TVWBB Honor Circle Bryan Mayland's Avatar
    Join Date
    Apr 2010
    Location
    Tampa, FL
    Posts
    4,707
    It is possible that the shock has flexed the thermocouple amp area of the board (which is easy do to the connector being held in the case). I'd try opening it up and taking a hot dry soldering iron (no solder) and placing it straight down on the leads of the thermocouple amp for ~5 seconds. Do as many leads at once a the point of the soldering iron covers at once. My 2mm tapered conical nestles nicely between two pins and makes good contact with both of them, so I just hold it there and count off 4 or 5 seconds, then remove the soldering iron and blow on the board for a few seconds to cool it. Do that as many times as needed to hit all the pins to sort of reflow the connection and see how it goes.

    All the SMD components can be hit as well, one connection at a time, again with a dry soldering iron just to reflow what is there. If you have a flux pen, it wouldn't hurt to get a little bit of that on each connection before you hit it. Should just take 1-2 seconds for the solder to go liquid again on all the components.

    If that's not it, I'd check the path coming back from the amplifier to the 100k resistor, the 0.1uF capacitor beyond that, and the connection to pin 28 (PIT) on the atmega and also make sure the socket isn't damaged.
    I'm that HeaterMeter guy what ruins everybody's free time.

  3. #3
    New Member
    Join Date
    Oct 2016
    Location
    Oklahoma
    Posts
    5
    Thank you Bryan,
    Looking more closely at where the chip is it is on the side where the thermocouple plugs in, but on the side of the raspberry pi. Opening the case and taking a look it doesn't look too bad, but there is one thing I noticed near the thermocouple solder points. There is a small rectangle "103" that is soldered in directly next to the thermocouple solder points, and one point appears to be bridging to the thermocouple solder point. Before I begin reflowing the solder I want to make sure that this bridge is normal? or if I should remove this bridge?

    I've looked through the soldering instructions and it doesn't appear to reference "103" so I'm not sure if this bridge is by accident or if it should be there.

  4. #4
    New Member
    Join Date
    Oct 2016
    Location
    Oklahoma
    Posts
    5
    Looking at the pictures a lot closer...

    https://heatermeter.com/devel/pcb/hm...e/step12-2.jpg

    it doesn't look like there's a bridge. Warming up the solder...

  5. #5
    New Member
    Join Date
    Oct 2016
    Location
    Oklahoma
    Posts
    5
    Actually also just realized something. I have a servo/fan housing that also hosts a thermocouple port. I have had the thermocouple plugged into this as well as the actual heatermeter. This make me think it might not be specific to the thermocouple plug on the actual heatermeter and more likely something to do with the circuit.

  6. #6
    TVWBB Honor Circle Bryan Mayland's Avatar
    Join Date
    Apr 2010
    Location
    Tampa, FL
    Posts
    4,707
    Quote Originally Posted by Robert Y View Post
    There is a small rectangle "103" that is soldered in directly next to the thermocouple solder points, and one point appears to be bridging to the thermocouple solder point. Before I begin reflowing the solder I want to make sure that this bridge is normal? or if I should remove this bridge?
    The 103 is the value of the resistor, 10+3 more zeroes=10000 or 10k ohms. There is one on both the TC+ and TC- connector and is part of one of the analog filters on the board. One side of it and the holes where each pin from the plug are the same pad so it is normal to see them bridged. The 102 (10+2 zeroes=1000 ohm) resistor is also on the TC- pad and the other side of it goes to ground, which forms the probe detection circuit.

    So short answer, as long as only one pad of the 103 is bridged to the TC- or TC+ hole, it is as intended.
    I'm that HeaterMeter guy what ruins everybody's free time.

  7. #7
    New Member
    Join Date
    Oct 2016
    Location
    Oklahoma
    Posts
    5
    Thank you Bryan,
    I've go through some of the solder joins, and did remove the bridge, though from what I'm reading that might not actually change anything. Doing a test burn right now, and thus far none of the symptoms from before have come back.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •