Electronics > Repair
BK Precision 2120 trace issues
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vexatag:

--- Quote from: bdunham7 on March 15, 2021, 03:13:14 am ---OK, what does the input to the soundcard scope look like?

And what is wrong with your signal at 10X?  We really want to use the 10X setting if possible.

--- End quote ---

Answering these questions with two images, first is the scope with the lead at the 1x setting, second with the lead at the 10x setting. I zoomed in and compared it to the unplugged second channel, it's just background noise. I can most likely test the other components on Monday, the school quarter is almost done and I have a few more assignments to take care of.

One more thing, when checking the board over I noticed that all the variable resistors on the board have some adhesive goop on them, but the application on the sweep length resistor is nearly non-existent, almost like someone has adjusted it. I'm not checking it out just yet but I've attached a pic of what I mean for reference.
bdunham7:
OK, soundcard 'oscilloscope' apparently has a low input impedance, so no 10X won't work.   :palm:

How do the probes connect to the soundcard?  There needs to be some additional resistance put in there somewhere.

vexatag:
Guess I should delay the testing process until it can be done safely, eh?

The signal chain is probe > BNC to RCA adapter > RCA Switcher > RCA to 3.5mm jack > 3.5mm cable > USB soundcard. Would it be a better idea to bite the bullet and get a different oscilloscope for testing? In my first 2021 update I mentioned that I was thinking of getting a DS212, so it would be within my budget.
vexatag:
Update, I bought a DS212 on Ebay, it should be here by next week.
vexatag:
DS212 arrived, it has built-in signal generation (square, sine, saw, from 10hz to 1mhz) and proper 10x attenuation support. I'm guessing I should hook the output channel of the 212 to the external trigger of the 2120 (dangerous potential for typos here) using a 10khz square wave, then connect the ground of channel A to the output channel ground and probe the points? Additionally, should testing be done with the 2120 on or off? It's been long enough that I don't remember how I was testing it.
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