I am using TL062 opamp in my design. Some of these boards are returning with erratic problem. The problem is , on my table nothing will happen for a day, then suddenly there will be noisy output with offset in output voltage. After few minutes it will return back to normal. There are 4 opamps in the same power supply. But all of them are behaving normally. Once I replace the opamp, then every thing will be fine. This is happening only in some of the boards.

Is this due to high gain in a single stage.

I am attaching the image of my circuit .

 

Cannot tell from scope shots if output going down to - rail or thereabouts ?

Some thoughts -

1) Bad solder joints
2) Pot wiper contact issues
3) If opamp in socket poor contact pressure on pins
4) Use PCB component spray cooler to try different parts
thermal behaviour, maybe a part, resistor, has manufacturing issues.

Regards, Dana.

 

I don't know if it's relevant in your circuit, but that op-amp won't work within a few volts of the lower supply rail. The common mode range includes Vcc, but not ground. Your circuit might be right on the edge, coming in and out of the common mode range?

 

I don't know if it's relevant in your circuit, but that op-amp won't work within a few volts of the lower supply rail. The common mode range includes Vcc, but not ground. Your circuit might be right on the edge, coming in and out of the common mode range?

I think this is going to be a problem unless the opamps have a negative supply voltage.

 

The schematic does not show if the power supply is positive only or plus and minus. Also its voltage is not shown so we are just guessing.

 

Cannot tell from scope shots if output going down to - rail or thereabouts ?

Some thoughts -

1) Bad solder joints
2) Pot wiper contact issues
3) If opamp in socket poor contact pressure on pins
4) Use PCB component spray cooler to try different parts
thermal behaviour, maybe a part, resistor, has manufacturing issues.

Regards, Dana.

I have changed all the components around the opamp.But problem is solved only after replacing the opamp.Opamp is directly soldered and I have checked all solder joints.

 

I don't know if it's relevant in your circuit, but that op-amp won't work within a few volts of the lower supply rail. The common mode range includes Vcc, but not ground. Your circuit might be right on the edge, coming in and out of the common mode range?

I am using +12/-12 bipolar supply and the usual signal level will be around +/- 2v near ground

 

The schematic does not show if the power supply is positive only or plus and minus. Also its voltage is not shown so we are just guessing.

Supply is +/- 12v . Could a missing bias resistor at non inverting input can damage an opamp. Since changing the opamp solves the problem.

 

I think this is going to be a problem unless the opamps have a negative supply voltage.

It is bipolar power supply

 

Supply is +/- 12v . Could a missing bias resistor at non inverting input can damage an opamp. Since changing the opamp solves the problem.

I don't think so, no. How about that 1K pot, could it be intermittent? You haven't shown if the wiper is attached to the negative rail.

 

I don't think so, no. How about that 1K pot, could it be intermittent? You haven't shown if the wiper is attached to the negative rail.

Wiper is attached to the ground. Moreover, I have changed the pot, but the problem persists

 

Hello,

Do you have decoupling capacitors on the boards fitted?

Bertus

 

Just a thought: Are you certain that the opamp is what you think it is -can you trace that particular opamp back to the assumed manufacturer?

 

Hello,

Do you have decoupling capacitors on the boards fitted?

Bertus

No . There is no decoupling capacitor. It is a dc measurement system. I will try this out. Thanks.

 

Just a thought: Are you certain that the opamp is what you think it is -can you trace that particular opamp back to the assumed manufacturer?

No. I am getting components from local vendor.But all other opamps in the same board at different locations are behaving properly. But since you suggested, I should pursue this thought.

 

Texas Instruments designed the old TL062 many years ago and make reliable ones. ST Micro make copies but I have never used anything they make and I do not know if they are reliable. They are not popular so I doubt that a Chinese guy makes them in his basement and sells them on ebay.

 

Some text removed for clarity)They are not popular so I doubt that a Chinese guy makes them in his basement and sells them on ebay.

On the other hand, for a high volume, low margin operation it might be profitable to remark an inferior opamp or worse a rejected and faulty opamp as a TL062.

What is difficult to diagnose is why the circuit would run for hours and then go through a "spell" of noisy activity and then return to normal operation. Those possible problems enumerated by danadak in post #2 are about it.

 

Hello,

Then read this thread why you need them:
Decoupling or Bypass Capacitors, Why?

Bertus

 

On the other hand, for a high volume, low margin operation it might be profitable to remark an inferior opamp or worse a rejected and faulty opamp as a TL062.

What is difficult to diagnose is why the circuit would fun for hours and then go through a "spell" of noisy activity and then return to normal operation. Those possible problems enumerated by danadak in post #2 are about it.

I was able to trace my supplier as Mouser. Brand is Texas Instruments. So probably something to do with my board. Today I am trying out the decoupling capacitor after which I will post the feedback.

 

If the symbol of Texas is upside down then it is a Chinese copy.