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Re: 7A22 Differential Amplifier Calibration

 

Can you make a measurement of the rise and fall times (check both just
to be sure) in the working configuration and non-working
configuration?

I do not remember what mainframe and timebase you are using but a 100
MHz mainframe like a 7603 and 100 MHz timebase like a 7B53A are more
than fast enough to do this. You may need to use the fast rise or
fall output from your PG506; I do not remember if the other outputs
are fast enough. The square wave output on my 3 MHz function
generator was not quite fast enough but only contributed like 10%
error.

My 7A22 measured very close to 350 nanoseconds which equates to a 1
MHz bandwidth. I am hoping that asymmetrical rise and fall times or
something about the difference between working and non-working reveals
something.

On Mon, 21 Mar 2016 18:54:14 -0000, you wrote:

...

I am attaching two photos which hopefully show the traces that I see. A 50mV
1KHz square-wave from a PG506 is connected to the +ve input of the 7A22 with
DC coupling in both cases. The photo ¡°Input+ve_Input ¨Cve GND¡± is what shows
when the ¨Cve input coupling switch is at ¡°GND¡±. It seems like pretty good
square-wave to me. The photo Input+ve_Input-ve DC¡± is what appears when the
¨Cve coupling switch is set to ¡°DC¡±. A rounding of the upper leading corner
can be seen. According to the Service Manual, the aberration should not
exceed ¡À1%. Is this so in my case and how can one estimate or measure that
anyway? If the 50mV 1KHz square wave is connected to the ¨Cve input, there
is no perceptible change when the +ve input coupling is changed between
¡°GND¡± and ¡°DC¡±.

I haven¡¯t adjusted C241 at all. It has occurred to me that some insect may
have crawled into the zone where C241 and C141 are located and died close to
C241, changing the capacitance just enough¡­..

Colin.
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