RPI and i2s->spdif power isolating problem

hi all

i just bought a i2s to spdif hat for RPI from aliexpress .it's a wm8804 based hat. the hat come with DC inlet and feed the power to RPI. i try to isolate the power of RPI and the hat by removing the gpio pin for 5v,3.3v and all ground. then feed both RPI and the hat with 2 external PSUs. then volumio and moode show error as attached. what did i done wrong 🙁 ? if anyone has any solution or resource please please let me know.

thank you so much.
Pu
 

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hi phofman

at first i started with cutting 2 5v legs and test. the problem started there. then i start cutting the 2 3.3v legs and all grounds. the problem still occur --' . i did test the ground after cutting all legs, the ground for RPI and hat still connect through PSU ground. then i disconnect the ground on psu, no luck --'. so maybe ground is not the problem.