Thermocouple build help


 
C

Christopher L

New member
From the wiki:

Before applying any power, check for shorts and good connections on the amplifier IC. 1 to 1, 2s to 2s, 4s are not connected to 5, and so on. N is not connected to anything.
Click to expand...

Should there be a short and/or resistance between 1 and 2 on the amplifier IC? I am currently reading 10.9K between these two pins. I have tried putting tons of flux on the pins and heating them. I have tried cleaning excess flux out of the way and blow drying the board with canned air. I have tried solder wick to desolder but cannot get the chip to come free. Nothing seems to get rid of the bridge if that is what it is. What makes me question myself is that I'm getting almost 11K resistance instead of 0K. For the record, both of the thermocouple circuit tests pass...
 
If you are looking at the picture you referred too. the amplifiers pin 1 is not shorted to 2. the only pins that are connected to each other are pin 2 and pin 3(picture show them as 2-2) and pins 5 and pin 6(picture shows them as 4-4). If your multimeter has a continuity check, you should not have any continuity between pin 1 and pin 2. you may have a resistance reading from it reading the resister(1n) between pin 1 and pin 2. If the other test are good then you must have it correct then.
 
Yeah you're just looking for shorts. If there's 11k resistance there's almost no possible way there's solder connecting them unless the solder trail happens to be a quarter mile long :) All you're checking for there is that no pins that shouldn't be directly connected (<1 ohm) are probing out as connected.
 
Question -
Doing thermocouple calibration now.
Have the probe in water at the moment.. temperature is bouncing all over the place between 141 and 149 degrees each second, at 5mv/c. Making it hard for me to get a steady reading to calibrate. Is that normal or did I mess something up?

hm4.png


Edit, I may have the polarity backwards.. brain fart, forgot red is negative in the thermocouple world. be back in a few to report

Nope, polarity was right.
Not sure why it's not staying steady, sigh. Don't have another K type to test with (ordered two and they sent me one wrong one :( )

edit 2 : I think I just have a crap connector or thermocouple or bad connection. Let it sit and finally stabilized, but, if I move it, it goes haywire. will report back
 
Last edited:
Well, everything tested fine during thermocouple assembly, but, I am guessing I goofed on something. Just re-doing all of the resistor mounts (chip looks OK but I'll go there if I have to) and one of my 1k connections sucked. Going to order another one and fix it up. Right now without it installed, the HM permanently reads 70F on the pit TC.

Thought I had a good solder job, oh well. Order extra resistors.. they are cheap, and if you're out of practice (or clumsy) like me, you may end up tearing off the leads or flicking one across the room by accident
 
if you are receiving a permanent 70F, its shorted somewhere. can you take a close up picture of the board, zoom in with your phone and take the pic as close as you can. They can get pretty close and its actually pretty good at seeing the connections.

example pic
208fer7.jpg
 
It's not a bad idea to ramp up the quantity on the SMD components that are cheap, as they are easy to lose and over heat, for a couple cents to have a few extra to just move on to the next one.... priceless....
 
John, will do, just waiting for those components to show. I removed the one resistor so can't make any determination until I get that back on. I do know what has to be done, just wanted to share my saga with the community. I will re-check for shorts, I actually take out my SLR with one of the big boy lenses then blow it up on the computer, easier to see that stuff. It tested fine during installation so not sure what I did after the fact, sigh.

Like Ralph said and I suggested too... extras are a no brainer. I am clumsy and should have done that in the first place.
 
in most cases, in a pinch, you could trace down the circuit and put a through hole resistor in place of a missing SMD resistor if you wanted, wont cause any problem.
 
When I rechecked all of the SMD components the other day, the only one I didn't like was the one resistor - one of the 1k's. They have such a small pad underneath that it's easy to burn it off.. given it was the first one I soldered down, it was definitely suspect.

Anyways, since they are pennies, just got 5 of each resistor ordered and just delivered from Mouser. Also got some guaranteed good thermocouples from Auberin's site, more expensive than the ones on amazon, but hey, I had to get something I know was good, I didn't trust the other.

Fixed up that 1K I didn't like, now temps are stable and looking good..

What's everyone's SMD soldering process?

Mine, not sure if it's right.. but I put a tiny bit of solder on each pad - not too much, did not want any domes. Placed the component over top with tweezers, held it down, then while applying downward pressure with the tweezers, tapped the pad with the iron and it pushed the component down into the pad.


On the amp, just did the same, but got Pin 1 on there solid before doing the rest.
 
You must log in or register to reply here.

 

Back
Top