This is the first thing you need to do, check all the main voltages. Or, with power sources, Often you can also find the faulty circuit by measuring the Ohms value, This are Ohm measurements from 3 motherboards, to give a overview.
in my dm800 the J1 or P5 is PS and main voltajes in the board: 1 -> 1.13 2-> 2.62 3-> 3.60 4-> 3.31 5-> 5.01 6-> 12.22 is a DM800 Rev: L year 2011, but is death, no oled display, only two lan leds on, no serial port, usb +5 no. possibly change the U26,U18,U11 and Y1 54Mhz or CPU?.
Hi, According to your fault description it could be a crystal issue, the Y1 which you can read at the Dm800hd death, no oled display, only two lan leds on topic. Caps replacement may also in some cases help, but if that is not the case, then it's mostly due the cpu or a print track interruption to or from it.