Bad temps when TC and food probes both plugged in


 
Geoff Parris

Geoff Parris

New member
I just soldered up my latest build last night and everything seems to be working great minus one little quirk: when both the TC and a food probe are plugged in, the temps are way off (in the 100's deg F). TC reads great by itself as well as all of the other probes, but both plugged in together = bad. Did the isolated TC testing and everything looked ok during install. Any ideas where to look first? I'm assuming there might be a short somewhere.

Pics of crappy soldering work: :eek:

https://goo.gl/photos/xfuPfmApygowyoxK7

https://goo.gl/photos/1k8ebW3TH4QSqk7Y8

https://goo.gl/photos/ciYUpb2zsXkyPHEZ9
 
It's hard to tell from the photos. The first thing I would check for is solder bridging on any of the solder points on the ports and the resistors/capacitors that are between them and the processor. Is it happening when you plug in a food probe into *any* port?
 
Jas E said:
It's hard to tell from the photos. The first thing I would check for is solder bridging on any of the solder points on the ports and the resistors/capacitors that are between them and the processor. Is it happening when you plug in a food probe into *any* port?
Click to expand...

Yes, I tried all 3 ports earlier and pretty much the same behavior.
 
If you have a way to test continuity with a multimeter. Some, like mine, have a setting that will beep when you touch the probes together. You shouldn't have any continuity between the TC and probes and the probes should have no connections between each of them.
 
First I would use rubbing alcohol and a toothbrush to clean the board between the ATMega and the probe jacks, it should get rid of that deposit of flux there around the SMD parts and could also knock loose little pieces of solder that could cause shorts. Then if that doesn't help, either use a magnifier of some sort or a closeup picture to inspect all the solder joints in that area for shorts. Since the soldering looks light on your probe jacks I would reflow solder to them, and to the resistors and caps that are standing up behind the probe jacks. Try to be very quick (though the large probe jack legs will take longer to heat properly), melt the solder and let it flow around the solder joint and component leg then remove the soldering iron quickly leaving a nice round deposit of solder that doesnt protrude out beyond the trace below.

As for the the probe circuits, they are fairly simple and should be independent and isolated from each other, as John has indicated already. The only thing they share in common really is gnd and they both use 3.3v, standard probes on the pullup resistors and the TC to power the TC amp. Here is a pic of the probe circuit schematic, the components circled are the R/C filters, the 10K resistors are the pullup resistors.

RCFilters.jpg
 
Last edited:
Thanks for the advice guys. So I ended up clearing all of that flux out and trying it again. This time it would work for a quick second, and then return a "no pit probe" error. Ordered a new TC and it seems to be working much better. I'm thinking I had a bad TC. So far so good :)
 
You must log in or register to reply here.

 

Back
Top