Cybershot E91:01 Flash problem

I got this camera with a broken screen and a stuck lens. I replaced both with working parts and reassembled everything. The camera can take photos, but the flash doesn’t work.

When I half-press the shutter button, the flash indicator blinks for a while, then an E:91:01 error appears and the camera takes the photo without using the flash.

I replaced the entire flash assembly, but that didn’t fix the issue. I also tried replacing the main motherboard, the flex cable, and even the whole casing. I’ve practically replaced almost the entire camera, but the problem is still there.

I also tested it with another flash assembly that I know works. When I inserted the battery and turned the camera on, the flash fired once by itself on the date/time setup screen, without pressing the shutter. After that, it didn’t fire again.

Does anyone have any ideas what I should check next?