Any good method to check smd opamps in circuit .

Hello everyone in this board .


Is there any reliable method on how to check SMD OpAmps in circuit ??
I have a bunch of SMD electronics cards full of these , and i can't remove each one and check it alone .

Which parameter do you want to check? Something like general working-ness?
If the opamp is in a standard configuration with feedback and is not saturated, then there should be very little voltage difference between the positive and negative inputs.

kubeek said:

Which parameter do you want to check? Something like general working-ness?
If the opamp is in a standard configuration with feedback and is not saturated, then there should be very little voltage difference between the positive and negative inputs.

Click to expand...

Hi , actualy the opamps i want to check belong to some multimeters , i just want to check them to see if they work properly or not .
Can i check them without any power an the unit ?? if not please give some methods .

no you cannot. Do you have a schematic to the circuit you are measuring?

No i don't have it unfortunately . i only have datasheets of the operational amplifiers .

more comments are very welcomed

Like I said in your original post. If the OP amp is used as an amplifier the inverting and non-inverting terminals should be about the same voltage. Anywhere from uV to mV apart.

Remember the OP amp has no ground. It may use a split supply or a single supply. When amplifying, biasing is USUALLY set to 1/2 the single supply voltage. e.g. For A 5V supply and amplifying an AC signal the DC output at 0V would USUALLY be about 2.5V

In your meters, the supply seems to be +-3 V. That 3V supply has a common. That is your reference.

With nearly anything, you always check the power supplies and the ripple. Since it's battery powered, that probably isn't an issue.

So, you can check the input (+ and -), the output and the supplies.

Outputs can be rail to rail. Check the specs. Even rail to rail, a 5.000 V output with a 5.00 power supply it's suspect. A 4.90 output with a 5V power supply may not be.

Without a schematic your guessing.

You can think of an OP amp as a device that subracts (A-B) and multiples it by a huge number. A is the (+) input and B is the (-input)

For the non-inverting configuration, gain happens when you feed back a fraction of the output. Ifyou feed back 1/10 of the output, you get a gain of 10.

When on OP am is used as a comparator, (A-B) is a big number, so it saturates at a rail.

One of your amplifiers may be configured as a sample/hold for Rel functions) and/or track/hold and or peak/hold. See: https://www.google.com/url?sa=t&rct...J9hkY66IPBH2LeA&bvm=bv.53537100,d.dmg&cad=rja These amps would not follow those rules.

You do have different modes and different inputs and auto-ranging. For the time being, you have to forget auto-ranging. Any saturated OP amp used in autorange will put the meter in overload.

If the OP amps work in the DC mode, they may be OK in AC. That would at least test those OP amps. RELATIVE mode in DC might check another to see if the REL measurement works.

You found one bad component and thus looked for stressed components nearby.

Just, post some readings of the amp in various modes in a range where the input would not be saturated. When looking for an AC problem, look at both the AC and DC inputs and outputs.

The 4066 may be involved with the REL circuitry or the input attenuator or something else.

Thanks KIS .

Am planning to remove the AD736 and check it , do you have any simple test circuits ?.

OK, if you want to test that chip, the only real part you need is a 33 uf capacitor and look at figure 35 of the datasheet.
You can basically set things up as in fig 35 for Hi Z and DC coupled.
Look the datasheet to see if the capacitor CC is used.
The decoupling caps sometimes are not needed for a quick test.
Use a bipolar supply like two 9V batteries.

J3 probably gets set to NORM.

If you use the DC coupled mode and bipolar supplies, voltages up to 1 V could be used, otherwise it looks like you have to stay below 200 mV.

I need to ask if you have a scope?

Ok i will se how to set this test circuit up .

Unfortunately i don't have a scope .