Thermocouple Works on RD3 but not on main board


 

NateSebold

TVWBB Member
So yeah the title says the problem. But I mainly run the RD3 and have no problems with it. Last night I had to run it without the RD3 and so I used a micro damper and the on board probe. About a half an hour into my smoke the thermocouple started jumping all over the place. At first I thought it was that I had a bad probe. So I swapped out the probe after doing so I noticed that my main probe had some issues at the plug.. it looked like perhaps the leads had been frayed so I stripped the wires and redid the the plug. I put it back in my smoker and fine for 30 minutes or so and then it just went dead. I finished my smoke by disabling the thermocouple probe and using one of the other 3 probe slots no problem.

So this morning I tried to check it out again and the on board thermocouple is still dead no reading on either of my two process. But I did hook up the RD3 and put the probes in and they both looked fine and registered fine.

So at this point I suspect a couple of things.

Something is wrong with my main thermocouple probe. As it stopped working last night and worked this morning on the RD3.

Something is wrong with my main board thermocouple port as it has completely died and the RD3 cross spliced in works fine.

Any testing or ideas or other thoughts?

Thanks beforehand to the great community here!
 
IDK how you wired in the aux thermocouple board on the HM, but if you did not use a switch then you'll have problems. You can only connect one thermocouple amp to the ATMega at a time, so you need to either lift (disable) the onboard TC amp and insert the aux amp, or lift the onboard amp and connect to a switch, also connect the aux tc board to the switch, then connect the switch common lead to the HM board.
 
Yes it has a switch on it. I checked all the wires and solder points of the switch this morning and they all looked good. I have used it many times before with the switched flipped to "local" so I know the switch works and that it has worked in the past.

Thanks Ralph! For jumping on so quick!
 
First thing to keep in mind is with the onboard TC and the Aux TC board you have TWO complete thermocouple amps. When switched to the RD3 and working that proves the RDTC board is working, your TC is good and the connection from the switch to the HM board is good (as well as the AUX side of the switch).

Your problem seems to be the onboard TC circuit (as you noted), so I would work backwards from where we know we are good.... We know the RDTC connects through the switch to the HM fine, to test the onboard side of the switch I would put the switch in the onboard position and then put a jumper wire between the common terminal and onboard TC terminal on the switch. If the TC functions normally you have a bad switch. If the TC is still malfunctioning you have something wrong on your HM board. Next thing I would check is the HM end of your wire for the onboard TC, ck continuity from the switch to the first component on the onboard TC amp. If you have continuity there then you should start to follow threads on TC amp circuit troubleshooting!
 
Last edited:
Thanks Ralph!

I tested all the continuities of the switch including all the way to the first component of the TC and had no bad connections.

I then began to follow the instructions here:

https://github.com/CapnBry/HeaterMeter/wiki/Thermocouple-Amplifier-Testing

I found:
1to1 good with no other connections
2to2 good with N also showing up
4to4 good but also 5&6
5to5 good but also 6
6to6 good but weird my multimeter beep for continuity was sort of struggling to come through but no other connections

I did not do the 9v test as the instructions warn against I also did not do a 3.3v test.. should I just use a AA battery and try that test... Also I'm not really sure I could read my analog multimeter fine enough to notice the drops that we are looking for.

Here is a picture of the general area I took with a macro lens on my phone:

https://www.dropbox.com/s/4wszuhyh27hhrgk/MVIMG_20180728_154335~2.jpg?dl=0

Any tips from here would be greatly appreciated.
 
IDK if it is just due to the picture, or flux buildup, but the 10N capacitor seems to have a bubble in it, and the other capacitor looks almost like a scorched edge, though that could a shadow. Hard to tell for sure from pictures at times.
 
To test a capacitor you would need to have it out of circuit and have a capacitance testing feature on your multimeter (Most entry level meters do not have this function). If you have the capacitor out of circuit you might as well just replace it instead of worrying about testing it. If you have to order parts I would order a couple of each part (minus the IC chip), these smd resistors and caps only cost pennies, might as well have them all on hand (and a spare or two in case you lose one when attempting to solder).
IDK if this is your problem , but you dont generally see bubbles in them, and nothing else jumps out at me visually.
 
I think the 10n looks ok, but I also see some poor/cold solder joints that could use a little redoing. I would also try and clean off that white cruft off the board.
 
Well hmph. I don't have much of an ability to fix these solder points nor replace the caps. I bought my board online and would most likely ruin it if I tried to solder it. It if was completely not working maybe I would attempt it but as it did work with the RD3 I am hesitant to do any solder work... anyway...

I do have an old toothbrush and so I brushed the heck out of the board and then plugged it back in to test and the local pit port came right up!!

Ugh not sure what the issue is. I am leaving it going for a while to see if the internal heat of the pi board is doing something.

I did plug in the liquid TC probe and not the probe that was involved in all the problems on Friday so I still wonder about the probe itself although I was also using the good liquid TC probe on Saturday when I was trying to diagnose the problem when nothing showed up.
 

 

Back
Top