I totally agree with Dennis.Normally if you ''pause'' your p/b &any portion of the pix is clear it's a good chance your heads are ok.A customer recently asked me about his 8mm video cam,which I no longer service,because of my 56 year old eyes ¬ too steady hand,if I though his video heads were bad on his unit.Normal p/b was very snowy,BUT,if he paused or did a forward search,the pix was clear.I told him I was almost 90% sure his heads were not the problem.Hope I did not steer him wrong....my 0.02c...Don ----- Original Message ----- From: "Dennis Viereck" <wa6ati@xxxxxxxxxxxxxx> To: <techassist@xxxxxxxxxxxxx> Sent: Sunday, November 25, 2001 10:06 AM Subject: [TechAssist] Re: Best way to clean a head. > > Larry: > > I disagree with your statement, "I takes 2 heads to complete a full picture". > If on head is bad and the other good you will be missing 1 field of video. If > you remember oUR NTSC format consists of 1 frame of video is equivalent to two > fields. The fields are interleaved together not appended to to the end of the > first field. > Since they are interleaved together one will end up with 1 line of video and 1 > line of snow then 1 line of video and 1 line of snow. This pattern will continue > throughout the entire video field. > > The reason you get a picture on half of the screen, usually the top, is because > of head protrusion. The surface of the head must impinge into the tape slightly > just after the entrance guide. This impingement depth must continue for the > entire 180 degree swipe of the video head "A" and repeat this process for video > head "B". > The main factor that effects head protrusion are wear. Obviously head wear is > something that only replacement is the answer. Insufficient back tension coupled > with head wear is usually responsible for the assessment mentioned, "even and > inch of video showing on the screen the heads are good" I would agree with in > part. > > As the video head travels around at 1800 rpm it creates air turbulence, This > turbulence does not negatively effect the entrance side of the drum assembly > where the tape meet the head. In fact the trailing side of the video head chip > had a lower pressure and will suck the tape in closer to the head. But after the > head has traveled 60+ millimeters to playback or record of the first video field > it looses the head to tape contact. One or two primary factors can cause this, > insufficient back tension and head wear. > > Any debris on the drum, or the video, or HI-FI heads can cause the tape to be > pushed away from the head trying to read it. This is why the air channels in the > drum must be kept free of any debris too. It is just as important as the video > head chips. > > > I have a brainteaser for the group. How many miles does single video head travel > in 1 single pass of a 6 hour EP VHS tape? > > Dennis Viereck > > > > > > > > > Ledstiles@xxxxxxx wrote: > > > In a message dated 11/24/2001 4:27:32 PM Pacific Standard Time, > > billmcfarland@xxxxxxxxxxxxxx writes: > > > > << > > > > > Howdy Wally, > > > > > If the heads are bad there won't be any video showing on the screen, > > if > > > > you have even and inch of video showing on the screen the heads are > > good, > > >> > > Wally . This above is sooooo wrong. Most bad head problems I run across have > > the 1/2 good picture display. I takes 2 heads to complete a full picture > > after all. > > Larry > > N.C.S. > > ================================= > > Help make your TechAssist database better! > > Submit your fixes here: http://circuitwork.com/techassist/tip/#tips > > ================================= > > To UNSUBSCRIBE your email address, click here: > > mailto:techassist-request@xxxxxxxxxxxxx?subject=unsubscribe > > ================================= > Help make your TechAssist database better! > Submit your fixes here: http://circuitwork.com/techassist/tip/#tips > ================================= > To UNSUBSCRIBE your email address, click here: > mailto:techassist-request@xxxxxxxxxxxxx?subject=unsubscribe > ================================= Help make your TechAssist database better! Submit your fixes here: http://circuitwork.com/techassist/tip/#tips ================================= To UNSUBSCRIBE your email address, click here: mailto:techassist-request@xxxxxxxxxxxxx?subject=unsubscribe