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The OP277 was a part made by Burr-Brown. BB were bought by Texas Instruments and the original part was discontinued and replaced by the TI OPA277 (even though the datasheet only states "Replaces OP-07, OP-77, and OP-177") All the letters after the numbers refer to package types and performance grades.


The OP277PA is an earlier version of the OPA277 precision opamp (Datasheet) If you scroll down to the orderable information you will find this the orderable part number for the device in a plastic DIP package. The final A refers to the die revision.


The answer is found in the OPA277 datasheet. Op-amps, particularly older designs, often are available in different grades. In the case of OPA277, the "A" grade device has slightly specifications: There are additional relaxed specifications for input current, CMRR, etc. So the basic chip here is the OPA277. The "P" suffix indicates the DIP package. And ...


Try loading it (shunting it) with, say 10 megohms or greater. This may help by loading open outputs, providing a discharge path for built up charge, etc. Worth a try.

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