In-circuit Test: how to test Op. Amps

Hi,

does anybody know how to carry out In-circuit Tests of Operational
Amplifiers?

for the sake of knoledge:
In-circuit tests are carried out by ATE machines with the target
unpowered (i.e. no power supply)

I read many Teradyne's articles but couldn't find anything useful.

thanks for any help,
Enrico

zigbee@libero.it wrote:
> Hi,
> 
> does anybody know how to carry out In-circuit Tests of Operational
> Amplifiers?

Back when the earth was populated with 709's
and 741's and I was a bench tech, I'd look to
see if the two inputs were within a few millivolts
of each other.


> for the sake of knoledge:
> In-circuit tests are carried out by ATE machines with the target
> unpowered (i.e. no power supply)
> 
> I read many Teradyne's articles but couldn't find anything useful.
> 
> thanks for any help,
> Enrico

On Apr 8, 3:19=A0pm, zig...@libero.it wrote:

> does anybody know how to carry out In-circuit Tests of Operational
> Amplifiers?

In high-volume CE, the _presence_ of _SOMETHING_ on the right circuit
nodes is used to verify that the chip is present, and a separate,
powered, functional test is used to check that the circuit is working
correctly. Or not, as the case may be.

The question can't be answered without first considering how critical
the application is. A cheap piece of CE will not be tested
exhaustively. A life-support system might get somewhat more analysis.

On Apr 8, 12:19=A0pm, zig...@libero.it wrote:
> Hi,
>
> does anybody know how to carry out In-circuit Tests of Operational
> Amplifiers?
>
> for the sake of knoledge:
> In-circuit tests are carried out by ATE machines with the target
> unpowered (i.e. no power supply)
>
> I read many Teradyne's articles but couldn't find anything useful.
>
> thanks for any help,
> Enrico

Hi
 You can't test an unpowered op-amp. You can
test the linear devices around it. Testers might
look for consistant resistance or voltage diode
drops. This is generally problematic with different
manufactures.
 As Jim says, when powered up, you should expect
to see zero volts difference of the + and - inputs. If
you don't, it may not mean that that amp has gone
bad but it is usually an indication that something
related has failed.
dwight