Re: 453 calibrator

Chuck Harris
 

People misinterpret things all of the time.

And people use their test equipment wrongly quite a lot.
I am not saying that is happening here, but it feels like
it might be.

If BA is truly at ground, then his scope is wired incorrectly.

Maybe someone measured BA to ground, found it wasn't, then
misinterpreting the schematic, added a jumper between BA and BB.

Maybe the coax has been subject to the soldering iron too many
times, and the center insulation is now shorted to the ground
braid.

The only reason BB is at ground is to ground the shield on the
coax. Purely a noise reduction issue.

-Chuck Harris

Mike Merigliano wrote:

Why would either BA or BB be a dead short (at ground) to Q1274's emitter? There is a
2.19K resister between the emitter and either BB or BA. I guess what I'm missing is
how someone could see a short on the schematic, even if they mis-interpreted the line
representing the board's boundary as a wire or trace. I am not an expert, so when
someone sees something on a schematic that I don't, I want to know why.

Connection BB is probably not needed when everything else is connected anyway, as
there are two other ground returns -- the one for the 1 volt BNC output looks
redundant to BB, and another 180 ohms kicks-in for 0.1 output. The other involves the
current-test loop, and there is another 220 ohms involved.

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