[vtech]

Your schematic in unclear but it looks like you may infact have a bad TL072. FET op amps tend to be sensitive and frequently do fail in audio applications.
There is no reliable way to test them--best to just replace it.

[damnick]

Hello to all
I have in repair a tascam us-122 audio card

The left channel is not working I have checked and the signal goes in but no signal arrive to akm4552 adc

It seems that no signal is also present on insert port
I think that the preamp is similar to this but
I cannot find some of the component because the board is small
[url=http://postimage.org/image/qucvjbgk/full/]
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I've checked and the collector of the transistor are connected like in this image to pin 2 and 3 of an opamp
but in the working channel I have a signal in output and the + and - at the same voltage with no signal present, and in the bad channel I have no signal on opamp pin 3 output and pin 2 and 3 are very different in voltage (2.8 and 1.8v) with +-5V supply voltage present and the output stuck at -5V

In what manner I can check if is bad the opamp, the transistor or some capacitor/resistor? the power supply are ok and the signal arrive at the base of the two transistor
Thanks for your help
Nicola Lunghi