Electronics > Repair
BK Precision 2120 trace issues
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vexatag:
I uploaded a video of the channel testing to Youtube, testing on a cheap 1khz triangle wave generator in addition to the calibration point.

12v and 24v test points are reading ~12v and ~24v respectively. I'm about to test the resistors.
bdunham7:
What happens at about 1 minute of your video is not clear to me--the dot splits up at an angle and I don't have a good explanation for that.  When you do channel 1, it appears to have a proper vertical response.  I'm going to have to think about that and I'm away for a bit, so test those resistors and don't give up yet.

If you don't find a problem, you should try turning XY mode off and look at it in the normal mode.  Figure out what moves the dot and what doesn't.
vexatag:
Tested all of the resistors to the right of Q807 in the horizontal final amp circuit (aside from R828 which I can't for the life of me find on the PCB). All of them are within an ohm or so of spec, with the exception of R838 and R839 (measuring at 15.92k and 14.97k respectively).

When I replaced the resistors, for some reason the normal mode wasn't able to come on the display at all. I fiddled with... something and got it displaying, the results are the same as in XY mode. Additionally, the x position knob is now functioning similarly in XY mode and normal mode, giving ~5mm of horizontal movement at the center of display either direction. The directions of movement are different, however. Channel 1 XY mode clockwise is left, normal mode clockwise is right. Channel 2 clockwise is left for both modes.
bdunham7:
OK, you need to stick with the normal mode for a while.  The normal mode will not normally show on the screen at all unless it is triggered or in AUTO mode.  So let's set this up for normal mode operation:

All six of the square pushbuttons in the 'out' position.  Coupling to DC/LF.  Source to CH1.  Connect the calibrator output to CH1 and set for 0.5 V/div for now.  Set the TIM/DIV to 1 ms/div, push in the center knob and make sure the XPOS/MAG knob button is pushed in.  Turn the TRIG LVL button to about the center and push it in.  Tell me what you have at that point.
vexatag:
I wasn't able move the center of the time/div knob in or out, but running all the settings as you said gives me two points stacked vertically, about 8 mm away from each other.
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