I have a Nec N9570a VHS, and am experiencing speckles and lines on screen during playback. I have cleaned the heads using head cleaning tape but problem not resolved.
Most likely, your video heads are worn out. Check it is worse on LP recordings. Worn heads result in many "tape droputs" which are horizontal speckled short noise lines. Before getting heads replaced, buy a new head cleaner tape to double check. Beware that head cleaner tapes are slightly abrasive, so do not over-use.