Summing Op Amp Circuit Troubleshooting

AI Thread Summary
The discussion revolves around troubleshooting a summing op amp circuit where the expected output is -5V. A participant initially calculated the output as -3V but questioned the correctness due to previous homework inaccuracies. After reviewing the calculations and signs, another participant suggested checking the polarity of a specific voltage input, which led to a revised output of 6V. The conversation highlights the importance of verifying calculations and polarity in op amp circuits. Ultimately, the group successfully identified the error and arrived at a correct solution.
Jayalk97
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Homework Statement


Solving for this circuit here, where V = -5V
upload_2017-2-20_1-16-36.png

Homework Equations


upload_2017-2-20_1-16-50.png


The Attempt at a Solution


I found the equation for a summing op amp like this one, plugged everything in and ended up with -3V, which is marked wrong. I'm really at my wit's end here and the homework has been incorrect in the past so I'm not even sure this is the wrong answer, any help would be appreciated.
 

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I think you must have a math error somewhere. Are all the signs correct?
 
TomHart said:
I think you must have a math error somewhere. Are all the signs correct?
I think so, I ended up writing it out and still got 3V
 
Can you post it?
 
TomHart said:
Can you post it?
Sure
20170220_013527.jpg
 
Check the polarity on the 4.5.
 
TomHart said:
Check the polarity on the 4.5.
Oh the sneaky bastards...
I got 6 volts for it thank you for your help!
 
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