If the USD version of firmware is 3.1, then it will not lock and the lock lamp will flicker WHILE A TAPE IS BEING PLAYED. Version 3.1 was made to behave this way as a warning to the user that raw, off-tape video is unsuitable as a clock source for the USD. The only solution is to process the raw, off-tape video through a timebase corrector (TBC), or better yet, get a video generator, feed it to both the VTR and the USD, and set the USD to sync to the video from the generator.Raw, off-tape video is a video signal, coming from a tape-based source, that has not gone through any processing to make it more stable. 99% of home VCRs and most industrial VCRs output this form of video. Some of the better industrial VCRs have circuits to clean up the sync portion of the off-tape signal. Some clean up the video signal by processing it through a timebase corrector (a sophisticated set of circuits which re-construct the sync portion of the video signal). In all cases, it's the sync portion of the video signal that the USD is "interested" in, and not the visible (picture) portion. The contents of the picture are totally ignored by the USD.