Electronics > Beginners

Beginners Road To Repair Part 2

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don@cascadefellowship.org:
Testing IC 2 in circuit.  TL072CN

Pin 3 connected to ground.  No pins shorted together.

Pin 1   Out 1   .748 volts (steady)

Pin 2   In 1-   .088 volts (steady)

Pin 3   In 1+   .002 volts (steady)

Pin 4   Vcc-    .753 volts (steady)

Pin 5   In 2+   .745 volts (steady)

Pin 6   In 2-   .207 volts (steady)

Pin 7   Out 2   .641-.646 volts (fluctuates)

Pin 8   Vcc+    15 volts (steady)

tpowell1830:

--- Quote from: don@cascadefellowship.org on October 03, 2018, 10:21:37 pm ---Testing IC 2 in circuit.  TL072CN

Pin 3 connected to ground.  No pins shorted together.

Pin 1   Out 1   .748 volts (steady)

Pin 2   In 1-   .088 volts (steady)

Pin 3   In 1+   .002 volts (steady)

Pin 4   Vcc-    .753 volts (steady)

Pin 5   In 2+   .745 volts (steady)

Pin 6   In 2-   .207 volts (steady)

Pin 7   Out 2   .641-.646 volts (fluctuates)

Pin 8   Vcc+    15 volts (steady)

--- End quote ---

I am unfamiliar with this setup and have not done much troubleshooting on such a complex board, just to qualify what I am saying.

To be perfectly honest with you, as some of the more accomplished board troubleshooters will tell you, these numbers mean very little unless you describe the setup that you are using for your test, such as what meter you are using, what is the settings that you are using, what is the input signal? Are these opamps there to accept the audio input? Do you have the schematic to show where and how these are used? Are you measuring AC or DC? Are you injecting a test signal on the input?

I am sure there will be 40 more questions from more learned people.

don@cascadefellowship.org:

--- Quote from: tpowell1830 on October 03, 2018, 11:09:32 pm ---
--- Quote from: don@cascadefellowship.org on October 03, 2018, 10:21:37 pm ---Testing IC 2 in circuit.  TL072CN

Pin 3 connected to ground.  No pins shorted together.

Pin 1   Out 1   .748 volts (steady)

Pin 2   In 1-   .088 volts (steady)

Pin 3   In 1+   .002 volts (steady)

Pin 4   Vcc-    .753 volts (steady)

Pin 5   In 2+   .745 volts (steady)

Pin 6   In 2-   .207 volts (steady)

Pin 7   Out 2   .641-.646 volts (fluctuates)

Pin 8   Vcc+    15 volts (steady)

--- End quote ---

I am unfamiliar with this setup and have not done much troubleshooting on such a complex board, just to qualify what I am saying.

To be perfectly honest with you, as some of the more accomplished board troubleshooters will tell you, these numbers mean very little unless you describe the setup that you are using for your test, such as what meter you are using, what is the settings that you are using, what is the input signal? Are these opamps there to accept the audio input? Do you have the schematic to show where and how these are used? Are you measuring AC or DC? Are you injecting a test signal on the input?

I am sure there will be 40 more questions from more learned people.

--- End quote ---

Yes, of course.  You make excellent points!  I'm using my multi-meter (Fluke 117) to measure voltages at each pin with the red lead while the black lead is on ground.  I'm measuring DC voltages. The unit is powered on with no input signal.  The Gain and Drive controls are all the way down.  I'm using this as an opportunity to learn what each pin represents on the op amp and I'm documenting the voltages to see if there are any obvious signs of a malfunction.  I should preface that by saying, I'm learning these things myself and would likely not recognize an obvious malfunction if it fell out the sky, landed on my face and started to wiggle.

I have not net been able to find a schematic so I'm open to learning how to draw one up from scratch while doing this repair.

That said, I'm open to any and all advice.  The more newbie oriented the better.  I have no formal training in electronics repair but I'm getting better at learning to identify components and research online.

tpowell1830:

--- Quote from: don@cascadefellowship.org on October 03, 2018, 11:21:15 pm ---
Yes, of course.  You make excellent points!  I'm using my multi-meter (Fluke 117) to measure voltages at each pin with the red lead while the black lead is on ground.  I'm measuring DC voltages. The unit is powered on with no input signal.  The Gain and Drive controls are all the way down.  I'm using this as an opportunity to learn what each pin represents on the op amp and I'm documenting the voltages to see if there are any obvious signs of a malfunction.  I should preface that by saying, I'm learning these things myself and would likely not recognize an obvious malfunction if it fell out the sky, landed on my face and started to wiggle.

I have not net been able to find a schematic so I'm open to learning how to draw one up from scratch while doing this repair.

That said, I'm open to any and all advice.  The more newbie oriented the better.  I have no formal training in electronics repair but I'm getting better at learning to identify components and research online.

--- End quote ---

LOL, that should be a classic, nearly fell out my seat on that one...    :-+

don@cascadefellowship.org:

--- Quote from: tpowell1830 on October 03, 2018, 11:30:32 pm ---
--- Quote from: don@cascadefellowship.org on October 03, 2018, 11:21:15 pm ---
Yes, of course.  You make excellent points!  I'm using my multi-meter (Fluke 117) to measure voltages at each pin with the red lead while the black lead is on ground.  I'm measuring DC voltages. The unit is powered on with no input signal.  The Gain and Drive controls are all the way down.  I'm using this as an opportunity to learn what each pin represents on the op amp and I'm documenting the voltages to see if there are any obvious signs of a malfunction.  I should preface that by saying, I'm learning these things myself and would likely not recognize an obvious malfunction if it fell out the sky, landed on my face and started to wiggle.

I have not net been able to find a schematic so I'm open to learning how to draw one up from scratch while doing this repair.

That said, I'm open to any and all advice.  The more newbie oriented the better.  I have no formal training in electronics repair but I'm getting better at learning to identify components and research online.

--- End quote ---

LOL, that should be a classic, nearly fell out my seat on that one...    :-+

--- End quote ---

All credit to Dan Aykroyd.

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