you either have leaking caps, or the optical pickup unit is toast. The disc usually doesnt spin if the PSD (position sensitive device) pickup cannot see the beam. if it spins and stops, it sees the beam, but it cannot see the proper levels to keep the PLL locked. either way, its a bad pickup unit. The high frequency whirring/hissing you hear comming from CD drives, and CD players is the loop noise from the PLL servo loops keeping the speed/positioning locked. If you have been working on CD players as long as I have, sometimes you can "listen" to these screams the drive makes to determine whether the PLLs are working on either extreme of the lock range.
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