While checking Vscan voltages on my LG du-42px12x picture died.

While checking the Vscan voltages on my LG du-42px12x screen ysus replacement board from ebay the picture went black why? I was checking the VSCAN and i believe the VY with a volt meter when the picture went black, but there was still sound.

I bought the LG du-42px12x with a bad ysus board(no picture just sound) replaced the ysus now the picture and sound work great but there are colorful dots all over the screen so i adjusted the VS and VA on powersupply to the factory settings, not much of a difference there. I adjusted the 2 knobs NOT DIRECTLY ON THE Y BOARD but are popped out attached to the ysus i believe they control black and white? i was able to minimized the dots and make them black but the picture quality went bad, now there are adjustment knobs on the board y_ramp etc that i dont really want to touch but i hear this control red green yellow (there are 3 on the board)

Also while checking the voltages on the ysus all of a sudden the picture turned off but there is sound(guessing the ysus board fried). Immediately i checked the voltages on the POWER SUPPLY to see maybe my power supply went dead the VOLTAGES are fine when the YSUS is disconnected but when i connect the YSUS the Vs Va voltages on the powersupply are completely off (appears the ysus is giving a shortage?), so i bought a new used ysus from ebay being shipped as we speak maybe that replacement y-sus board was bad but what if the new one im getting has the same problem? what else could it be and why do you supposed all of a sudden the ysus fried just from checking voltages on the ysus?