strange problem with my Spectrum

Hello All! Please tell me: all tests crash (in turbo firmware from 1991), and after resetting the screen filled with flickering noise reminiscent of multicolor (or something like that when The CPU signal is not soldered into the memory expansion circuit). What's the strangest thing, NEW normalizes the picture. clear, out on all ports with different numbers - nothing gives. The memory test is successful, in TEST 4.22 garbage appears when The DATA test starts and the drive turns on (What kind of test is this anyway?). C 50/50 chance it either freezes after a few seconds of garbage on the screen, or is reset, and the picture, as I already said, is dirty until you press reset or new. SYS.TEST is reset somewhere in the AY test area (where these tests pass very well quickly and it’s impossible to keep track of which one crashes). Some programs work fine, some have garbage on the screen (for example, in 3x color graph. in the editor the pictures are displayed normally, but when clicking on "help" icon, the text becomes unreadable. Tell me where to dig? I’m already completely exhausted over this firewood. Sincerely, Yura AKA d00RsFan [ZX] [D00RS] [IRCNet#Z80]