Electronics > Repair
BK Precision 2120 trace issues
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bdunham7:
OK, let's back up (again) and make sure your new scope can give you a proper reading.

Are you not using a ground clip on the scope probe?  I believe I may have told you not to, but I'm not familiar with your little scope and it may have isolated inputs, so lets try this:

1) Don't use the signal generator at all--disconnect it and set the leads aside
2) Use the LINE trigger setting on the BK2120
3) Use one probe on the scope and connect the ground clip securely, preferably to one of the BNC shells or alternatively to the frame of the instrument.
4) Try again, starting with pins 7 and 14 of U603.  You need to be able to see 0 (or so) volts and 5 volts (4.3 is probably OK) just as your multimeter shows before proceeding.
5) If that works, start looking for the 60Hz line trigger signal, starting again at the switch pins, then pin 9/U601 and pin3/U603.  Screenshots are needed here.
6) If those look good, then pins 5 and 6 of U603.
vexatag:
I have been using the ground clip on the new scope, yes. Additionally, I've stopped using the external signal generator and have instead been using the new scope's built-in function generator.

The first two screenshots are from the slope switch with coupling set to LINE. When the ground cable was connected to the chassis, I got 4.3 volts to show up on pin 14 once in like 20 minutes of testing at various timebases, however when I checked without the ground cable connected I instantly got a reading. That reading is in the third screenshot. Going to hold off on testing the rest of U603 and pin 9 of U601 until you've had a chance to analyze this information.
bdunham7:
Is there an option in that scope for AC and DC coupling?  Pin 7 of U603 should be a more or less flat line at about the level of the A channel marker and pin 14 should be a flat line about 5 volts (2.5 divisions) higher than that.
vexatag:

--- Quote from: bdunham7 on March 22, 2021, 08:20:49 pm ---Is there an option in that scope for AC and DC coupling?

--- End quote ---
The DS212 has AC/DC coupling, yes. I've been using AC coupling in all the readings so far.


--- Quote from: bdunham7 on March 22, 2021, 08:20:49 pm ---Pin 7 of U603 should be a more or less flat line at about the level of the A channel marker and pin 14 should be a flat line about 5 volts (2.5 divisions) higher than that.

--- End quote ---

Just checked this in DC coupling and you're correct. Going to go ahead and check the remaining pins in DC coupling.
bdunham7:
Change to DC coupling and try all that again!
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