Two Identical circuits with one difference[Solved]

Thread Starter

Deltafee

Joined May 22, 2015
33
Hello,
I have built a circuit, that is composed of two of circuits seen in the circuit diagram; my problem is that one of these circuits works correctly and the other doesn't. The key difference is the voltages between the 383kohm resistor, on the side of the resistor with the black arrow the voltage is 2.96V for both circuits, but on the circuit that works the voltage on the other side of the resistor(red arrow) is 2.69V while on the circuit that doesn't work the voltage is 2.47V. Both circuits have the same components and are within the proper values of each other, I checked to see if there were any shorts but have not found any while also checking to ensure there are no cold solder joints. I would appreaciate any help on figuring out how get this thing working.
Thanks,
 

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Colin55

Joined Aug 27, 2015
519
The image is such poor quality that I cannot see the values of the components. It has to be a .gif with a single pixel for each line or value. Just like all the circuits on Talking Electronics.com website.
 

AlbertHall

Joined Jun 4, 2014
8,313
The blue LED can only ever be reverse biased.
The transistor feeding the blue LED is PNP and has its collector connected to the positive supply - wrong!
Is it only the blue LED which doesn't work?
 

Thread Starter

Deltafee

Joined May 22, 2015
33
Okay, so here is a better quality picture. So the blue LED is just an indicate that the device is working which one of them is. This measures the EMF as a EMF is applied it lights up from green to red, the only addition is the two op amps that connect to both sides of the other color LEDS and works fine(They allow me to measure the voltage between the LED). The One circuit that works when powered on lights up all LEDs and then they turn off only to have the Blue LED lite, then works as stated before, which mimics the K-2 meter I reversed engineered. The second one has the green LED constantly lite and does no change and will not behave like the other one does when and EMF is applied. It works as a differential op amp and the problem is that voltage. I will post more when I get around to observing more behavior.
 

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