Before opening your SV04 you may want to run heatbed PID-tuning. The process is described here.
If that doesn’t help opening the SV04 case is not that big thing: Disconnect the power cord first, then turn SV04 sideways carefully iot not to damage the gantry & keep the highest extruder from moving & crashing into the other extruder. Use a Philips screw driver to remove the 8 bottom screws, remove the bottom plate. The relevant heatbed cables for examination are located in the bottom left corner of the motherboard. Documention is available on page 29 of the SV04 user manual.
Good luck
Björn