Author Topic: Moar IC voltages pins 4 and 8 swapped  (Read 1190 times)

sangster

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Moar IC voltages pins 4 and 8 swapped
« on: October 15, 2018, 12:06:58 PM »
Hi all! The title says it all... Noob question here. Just put the Moar together and am reading the IC voltage at pins 4 and 8 as 9.41 (@ pin four) and around 0 (@ pin eight). This is the opposite of what it should be. Any ideas on why this is the case?

Thanks!
« Last Edit: October 15, 2018, 12:16:57 PM by sangster »

Ralfg

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Re: Moar IC voltages pins 4 and 8 swapped
« Reply #1 on: October 15, 2018, 12:17:52 PM »
Check to see if either the IC is in backwards or you have the ground and +9 volt wire in reverse.
Dr. Von Fuzzbrauer @ Rocket Surgeon Effects Pedals
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sangster

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Re: Moar IC voltages pins 4 and 8 swapped
« Reply #2 on: October 15, 2018, 12:27:07 PM »
Checked both. They should be correct...

Ralfg

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Re: Moar IC voltages pins 4 and 8 swapped
« Reply #3 on: October 15, 2018, 12:48:57 PM »
Next thing to check is make sure your power supply is center negative. You can do that by putting the negative of your volt meter leads into the barrel and placing the other on the outside. Make sure it reads +9. Also how are you connecting it to your wires for testing?
Dr. Von Fuzzbrauer @ Rocket Surgeon Effects Pedals
https://www.smallspacesband.com/

sangster

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Re: Moar IC voltages pins 4 and 8 swapped
« Reply #4 on: October 15, 2018, 01:12:08 PM »
I'm using a onespot (center neg) plugged into a typical jack. The image I've attached doesn't show the jack because I snipped it off to test flipping it around...

madbean

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Re: Moar IC voltages pins 4 and 8 swapped
« Reply #5 on: October 15, 2018, 01:44:10 PM »
That's an unusual looking IC. Where is it from?
No matter where you go, there I am. Watching you.

sangster

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Re: Moar IC voltages pins 4 and 8 swapped
« Reply #6 on: October 15, 2018, 02:08:21 PM »
http://www.smallbear-electronics.mybigcommerce.com/ic-mc1458p-ti/

"IC MC1458P (TI)
Product Description
Dual bipolar op-amp used in many classic distortions and ODs
Replacing LM1458 (obsolete)"

sangster

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Re: Moar IC voltages pins 4 and 8 swapped
« Reply #7 on: October 15, 2018, 02:20:03 PM »
I am using a Schottky 1N5817G in place of a regular 1N5817 at D9. Would that make a difference?

madbean

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Re: Moar IC voltages pins 4 and 8 swapped
« Reply #8 on: October 15, 2018, 02:45:26 PM »
I am using a Schottky 1N5817G in place of a regular 1N5817 at D9. Would that make a difference?

None at all. What are your voltage readings on both sides of the 1N5817?
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sangster

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Re: Moar IC voltages pins 4 and 8 swapped
« Reply #9 on: October 15, 2018, 03:00:55 PM »
9.41 on the inline side and 9.27 on the other.

madbean

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Re: Moar IC voltages pins 4 and 8 swapped
« Reply #10 on: October 15, 2018, 04:48:37 PM »
Well it's a bit baffling how you could have 9v on the 1n5817 and not on pin8 of the IC since they are directly connected. Are you sure you haven't confused pins 4 and 8? If you look at the trace diagram in the build doc, pin8 is the one connected by the fat red trace and pin4 is the one that appears to have no connection (it's actually connected to the ground plane).
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sangster

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Re: Moar IC voltages pins 4 and 8 swapped
« Reply #11 on: October 16, 2018, 08:44:37 AM »
So I messed around with it more last night and I think my problem was a short in the circuit. I can't see where it's happened, but after physically manipulating the thing, it's seemed to go away. Sorry for the rookie mistake... ugg... and thank you for your help!!

Ralfg

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Re: Moar IC voltages pins 4 and 8 swapped
« Reply #12 on: October 16, 2018, 09:34:34 AM »
Glad you figured it out. Should have suggested reflowing everything.
Dr. Von Fuzzbrauer @ Rocket Surgeon Effects Pedals
https://www.smallspacesband.com/