Electronics > Manufacturing & Assembly

T962C reflow oven mechanical advise needed

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JayGunn:
I just (impulsively) bought a like new but 10 years old T962C. I am facing the obvious issues all buyers have had.

I want to reduce the bogus temperature readings I get for a sample board with my own thermocouple on it. If I pre-heat the oven, I get e.g. 205C from the oven reading when my own thermocouple reads 183C on the board.

Yes I could scale my profile(s) to compensate, BUT on cool-down I get the reverse effect--the oven thermocouple reads way COOLER than my (perfectly good) thermocouple.

I want to lower the oven thermocouples down to very near board level, i.e. about 1/2" above the drawer bottom. I think both heating and cooling measurements will be closer to the truth this way. Right now both thermocouples are really close to the middle 2 IR tubes--they'd have to be way off up there.

The mechanical issue is that the thermocouples pass through stainless tubes and the top of the tubes are crimpled really deeply. Do you guys have any suggestions about how to relieve the crimp enough to lower the thermocouples? I will (eventually) gently re-crimp them when I find the sweet spot.

TIA

John

tomgat:
I use a T962C daily and have used it for thousands of boards.  Its a great little oven, but definitely has its quirks.   Board placement position REALLY matters, which I typically do by putting a test board in. 

As far as the thermocoupler being off, yes this is a problem.   The way I "fixed" it was upgrading the software (there are several links online to doing this), and making the hardware adjustment.  Then I just set the thermocoupler gain on the down to adjust it closer to what my thermal test probe says.  On mine, I think its set to 82%.   

tomgat:
Also, as far as lowering the thermocoupler, I did this at one time on one of my older T962s, didnt find it helped much.  I also added a mechanical fan, which equally didnt do much. 

You can move it by "uncrimping" it with a pair of pliers and then recrimping it.  On mine, I added some high temp epoxy to make sure it held in place. 

JayGunn:
Thanks for the replies. I had tried a tentative squeeze 90deg offset from the inward dimple, didn't see that it had any chance of popping out the depression so I gave up. I can try harder. Also I considered finally treating myself to a Dremel tool and one of those very thin cutoff wheels and just barely cutting through the top 1/2" (sorry, 12mm). I think I'll try a more forceful pliers attack first, Dremel second and...

What I didn't know is that the open source software/firmware upgrade would allow scaling the thermocouple values. That's very tempting. So that's Plan C or III or 3 I guess.

Thanks!

jmelson:
If the thing in the photo is actually the thermocouple, it is WAY too big.  I have a converted toaster oven, and I poke a micro thermocouple into a plated through hole in the board to measure ACTUAL board temperature.  My thermocouples are made from about #30 AWG wire, same size as wire-wrap wire.  This allows the controller to sense actual board temp.  It works like a charm!  The problem you are seeing is thermal inertia.
Jon

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