Hello, I recently just fished putting my QMX Rev 4 kit together with the windings necessary for 12v input. As I was going along I verified I all continuity checks as instructed and verified no pads were bridged. Upon attempting to power on the device, I connected my 12v power supply to the barrel connector. The screen immediately lit up and I had black rectangles across the top half of the screen. A second or two later I started seeing smoke, heard a pop, and the screen went dark. Upon further inspection, I was able to discern that the Q108 MOSFET on Plug-in PCB #1 blistered and exploded. The L101 inductor nearby also looks a little singed but the enamel coating does not appear to be compromised. I do not see any other areas of the device that appear to have been compromised or damaged.
I was wondering if anyone may be able to assist with what actually went wrong here. I have ordered a new power supply board as well as a replacement MOSFET to try my hand and replacing the bad component.
My current theories on what went wrong are:
- I am missing a bad solder joint somewhere that caused the issue, still attempting to find one if so. It's still unclear why the MOSFET would blow in this case as it's rated for 20V and my power supply used is only capable of 12V out.
- There is a step in the instructions that says to bend a tab of the LCD screen at about 45 degrees to clear the L101 inductor. I noticed that this appears to have been discolored possibly due to heat. There's a good chance that this tab was not bent quite enough and made contact with the top face of the L101 inductor, though I don't think the top face is conductive. This could have resulted in a short to ground?
- My winding on the RWTST Transformer is somehow incorrect.
Image upon powering up. Seconds before smoke and pop.?
Note: I did not press the left dial in, the screen lit up as soon as power was supplied to the barrel connector.
