There are different versions of the CH340 chip. The CH340G requires the crystal oscillator along with the C5 and C6 capacitors. The CH340C has all that circuity built into the chip and doesn't require any of those 3 components.
It looks to me like this is set up as RS-232 serial communications. If your computer has a DB-9 serial port, you should be able to connect pins 2,3 and 5 directly up to the excavator, without the need for a fancy custom cable. Also, a standard USB->Serial cable should work as well.