Author Topic: How can this be?  (Read 2401 times)


How can this be?
« on: August 18, 2020, 05:28:48 PM »
I have built this circuit a few times, and successfully.

This time around however, i decided to change the op amp and use the 4558D op amp.

While I was building it, I was paranoid about building the voltage divider part of the circuit, and so i tested it with a meter along the way. It was sending the correct voltage.

I built the entire circuit and the meter measurements from the negative terminal of my 9 volt battery, and the various pins, seemed to be okay. (I shorted pin 6 and 7) to disable the second part of the op amp.

But all of a sudden, without my changing anything, all of my measurements from all the pins on the op amp, shot up to over 8 volts. Even Pin 4 , which is suppossed to be ground, is over 8 volts. 

How can this be? Even the point of the volktage divider where it should read half the voltage, is over 8 volts. See attached pics (my build, front and back and the schematic i am building from)

P.S. Here is the datasheet for the op amp.

I did not know what to do with Pin 5. Was I supposed to send that to ground- is that what could have caused this?

Thanks for your time.

« Last Edit: August 18, 2020, 05:31:50 PM by Guitarist335 »


Re: How can this be?
« Reply #1 on: August 18, 2020, 09:43:53 PM »
How’s your battery?

I think you may have some shorts in your board... try reflowing
flip flop flip flop flip


Re: How can this be?
« Reply #2 on: August 19, 2020, 06:32:53 AM »
Sounds like you may have lost your ground connection.
Ohm's Law - much like Coles Law, but with less cabbage...


Re: How can this be?
« Reply #3 on: August 19, 2020, 06:44:51 PM »
Thanks guys.  Will check it out