thermocouple output reads 0v


 
J

Johannes S

TVWBB Member
i lately decided to retrofit the thermocouple parts which i got from peter f (thanks again for the fast service!).
everything went on fine, i don't have issues soldering smd parts and have the appropriate tools for it.
i tested it and got readings of 400°C w/o anything connected. stupid me i had R18 soldered in, as this was a thermistor port before. pit input pin was reading 2.0v at that time. supply voltage for the amp was 3.3v.
so i removed the 10k R18 and measured again. now pit input pin reads ZERO volt 0.000 - no matter if a probe is connected or not. i tested all connections to and and from the amp and tested all pins for shorts. no shorts, and all pins show cc to the relating parts on the board as shown in the trouble shooting drawing.
so what could i test next? any how to test the amp? anything else to test? did i burn the amp when R18 was installed and power was applied?
thanks!!
 
Have you changed the settings on the webpage. You should see about 23° on the display, even if you did not change the settings.
 
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i reads ZERO volt at the thermocouple output. no matter what i set the software to, this won't change. and yes, it is set to thermocouple.
the question is mainly hardware related i guess. i don't know how easily those amp chips die or what destroys them.
 
I'm not sure what kills them either, they seem to be really resilient at times then fragile at other times. I've definitely built one with the 10k resistor installed by mistake and it recovered just fine once the resistor was removed, and others have reported this as well. If it is reading 0V at the output I'd say it is toast though. When I had the 10k resistor installed, it read as "off", around 3.1-3.2V. The amp itself can't even pull the voltage down to 0V, so either the output trace is grounded (easy to check), there's no 3.3V power (you've already checked) or the amp is kaput.

If you desolder the amp from the board, you can hook REF and GND to GND, and VCC to 3.3V. You should get 3.1-3.2V on the output. All the other components are decoupling and noise reduction so at this basic level you can see that your amp is dead right before you toss it.
 
Bryan Mayland said:
If you desolder the amp from the board, you can hook REF and GND to GND, and VCC to 3.3V. You should get 3.1-3.2V on the output. All the other components are decoupling and noise reduction so at this basic level you can see that your amp is dead right before you toss it.
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thanks. so i'll do that and check and maybe order a new one. resistors are measured and working, caps would be no issue, and traces are all ok and not shorted. we'll see.
 
IDK for sure, but if the REF pin is not grounded or supplied a voltage (if the REF pin is floating), won't the output of the TC be 0v?
 
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