Does anyone know a location to get a datascheet for the IC: "1GM1-4239"?
This IC is used in the 50-Ohm front end of an Agilent DSO9254A. I think it works there as a programmable amplifier or attentuator.
In the DSO9254A i try to repair, this "1GM1-4239" shows the following error:
While in the upper input ranges (50mV, 100mV, 200mV, 500mV, 1V) anything is OK, in the lower input ranges (1mV, 2mV, 5mV, 10mV, 20mV) the "1GM1-4239" injects a current of about -0,2mA into the 50-Ohm input resistor.
This results in an offset voltage of about -10mV at the 50-Ohm input. Too much to be compensated by the auto calibration...
As a quick hack - far away from any professional repair - i connected a 25kOhm resistor beetween +5V and the 50-Ohm input. The resulting current across this resistor (+0,2mA) compensates the DC offset to 0V.
And after this "hardwired compensation" astonishingly all other parameters, the channels voltage sensivity, its frequency response and rise time are fully in the specs, and equal to the remaining three channels of the scope.
The "only" fault of the "1GM1-4239" seems to be the strange input error current in the lower ranges...
Many thanks for any help!
Kind regards