OP amp Comparator not working any tips?
You are trying to use the LM139 outside of its Common-mode input voltage range:



I deduce from your question that you are using a supply voltage of 6 V.
That means that the Common-mode input voltage range is between Vcc - 1.5 V = 4.5 V
and 0 V. Your input voltage are higher than that at around 5.0 V

So you will need to increase the supply voltage (I would choose at least 7 V).

Or you use a voltage divider to lower the 5 V input voltage to for example half of that: 2.5 V just to keep things simple. Then of course you will also need to halve your reference voltage.