I am a bit of a noob, and I have acquired a huo STTNG that does weird random things. During gameplay it will display "open coin door to use buttons", it will show the spinner value when pressing a flipper button, and sometimes all three flippers will go crazy and engage by themselves. The flippers will stop when either flipper button is pressed, but start again when the button is released. Sometimes (not always) I get flipper EOS switch stuck closed and/or GND Short Row 1, sometimes all the balls shoot into the trough, sometimes a coil underneath the playfield starts firing. Turning the game off and on again usually fixes everything and the game will play again, until it doesn't. I have looked for loose wires or obvious physical problems, but see none. U20 is soldered, but that seems to be a common suggestion - help?