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Do not detect any drop pulse at TONA/B at least?
Check all SPI termination resistors and traces around U6100.
You can also try new BIOS.
Can you see if U2600 sends out 25MHz at pin 9, or if tries at least?
TONA voltage is completely unusual.
Check all resistors and traces around U7400.
Does it get 5V at pins 19, 29, 46?
3V present at pin 47?
Also check all its MOSFETs; replace them, just in case.