Electronics > Beginners

Bogus parts from Reputable Dealer?

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rstofer:
As pointed out, all measurements between pin 2 and pin 6 seem to be off by an order of magnitude.  If so, all of the offset voltages are in spec.  The simple output voltage test leads me to believe all of the op amps are operating correctly.

Later you can try a 1k load to Vdd and then again to Vee and do the simple voltage measurement again.  This will show whether the output stage can actually drive a load.

All of the devices look good to me - assuming there is a decimal point error in the offset voltages.

Jwillis:
I don't know whats going on . The meter is auto ranging . I only have meters that go down that far .

Jwillis:
So if can I  compensate for the offset  externally with a single supply or do I still need a negative rail to adjust the offset ?

ebastler:

--- Quote from: Jwillis on January 21, 2020, 04:04:47 am ---I don't know whats going on . The meter is auto ranging . I only have meters that go down that far .

--- End quote ---

Your offset readings (measurements between pins 3 and 6) look implausible, especially in view of the very precise and reproducible output voltage (pin 6 to GND). As you have separately measured pin 3 and pin 6 to be at 4.535 .. 4.536 V, stable to within a mV, why would you see more than a mV of difference between them?

Please have another look at your multimeter(s). Most auto-ranging meters have a manual range selection pushbutton which you can use to select the most sensitive voltage range, and avoid the potentially confusing auto-ranging.

Also, could you connect a scope in parallel to your voltmeter when you take those readings between pins 3 and 6? Just to check that no AC noise gets introduced during this measurement. You are connecting some nice long "antennas" there, with the multimeter's probe leads. [Edit: And no oscillations due to an unwanted positive feedback loop, coupled via the probe leads.]

wraper:
In addition to said above, try attaching some 0.1-1uF capacitor in parallel to one of 4.7k resistors (does not matter which) in voltage divider and measure offset again.

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