Re: 453 calibrator

Mike Merigliano
 

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.

On 5/9/2018 12:29 PM, Chuck Harris wrote:
No, you aren't missing anything. What Jeff was saying
is if BA is truly at ground, then you cannot have a signal
out your calibrator. It may appear to be grounded if you
use an ohmmeter that is on too high a scale... due to the
160, or so ohms that the circuit inherently has to ground.

-Chuck Harris

Mike Merigliano wrote:
The signal is not shorted to ground -- it goes through a 2.19K resistor in series
first, so there is no short. My Tek 453 has a calibrator signal, at specification. My
ohmeter and voltmeter check measurements between/around Q1274, point BA, R1274, and
point BB match what is on the schematic.

Maybe I am missing something.

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