LabGuy's World: Most Frequently Asked Question #5

Q.     I have my machine hooked up and threaded correctly. But, when I play the tape, I can only hear the sound but the screen is full of snow / blank. What is happening?

A.     This is the classic symptom of clogged video heads. (Presuming the electronics are OK) Using a brand new or very clean piece of chamois cloth, saturated with denatured alcohol, gently wipe the face of the video head back and forth, NEVER up and down! Examine the chamois and you should see the black oxide coming off the heads. Move to clean spot on the chamois and keep cleaning until no more dirt appears. TIP: remove the top covers of the head drum so that you can gently rock the head bar back and forth with one hand while pressing the chamois gently to the face of the drum with the other hand. The JVC reel to reel VTRs actually have an opening in the metal part of the head cover allowing the user to do this without opening the drum completely.
        The swab shown in the photo above is especially made for cleaning video heads. It is a plastic wand tipped with fine chamois or foamed plastic. These are available from [Comprehensive Video Group] and many other video supply companies.
        DO NOT use Q-tips or cotton tipped cleaning swabs! These leave fibers behind which can cause problems of their own. These same fibers can also hook around the heads, which are about as strong as sharpened pencil lead, and break them right off when you pull the swab back. In desperate cases, I have used clean white paper soaked in alcohol. Beware that after one or two strokes, the fibers in the paper will begin to behave like the Q-tip. Another useful cleaning tool is round toothpicks. Use these to clean in the corners of the tape guides where oxide tends to build up causing mis-tracking. They ae useful also for prying out extreme cases of dirt. NEVER use metal tools to clean the tape path! Dental picks may be ok for cleaning guide edges, but they scratch deeply and may be magnetic. Just don't use them, no matter how tempting this may seem. Remember, you can't get replacement parts for these machines anymore!
        After cleaning the video heads, move on to clean the face of the drum and all other surfaces that come into contact with the tape. You must do this every time a shedding tape has been played. Otherwise, the binder residue on the guides will be transferred to the next tape you play rendering it unplayable as well.
        If the heads quickly clog again, it may be possible that the tape is breaking down and shedding. If possible, try playing a known good tape. If the chronic clogging continues, it can be due to a chip in the leading edge of one or both video heads. A leading edge chip behaves like a knife edge, scraping up oxide from the tape and clogging the video head. A pocket microscope can quickly identify this problem. The face of the head should be clean and unbroken. The leading edge of the head should slope away at an angle like the tip of an ice skate. If it looks like a brick with one corner knocked off or, worse yet, the head looks like a broken glass bottle, then that head will need to be replaced.

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Last updated: January 11, 2005