Doubled up video head appearence?

[N_Cook]

N_Cook wrote:
By replaced, do you mean robbing a brass plus ferrite plus shim plus coil of a head from a donor drum ? what sort of basic/sophisticated physical xyz alignment of the head did you do before reassembling and and powering up ?

VHS heads are screwed in the drum and electrical connections soldered so they can be removed as a chip, see example:
http://www.danalee.ca/ttt/images/12/sixheaddrum.jpg
I took a similar head from another drum and installed it matching the position of original head as best as I could by eye. I did some markings on the drum before I took out the damaged head to keep a reference of its position. Then I did a fine position calibration by watching the resulting video signal, removing and reinstalling the drum back in the machine every time to make small corrections. There is another screw not shown in the photo that sets the head separation against the drum adjustable from the top.
The video signal tells a lot about head calibration problems. The resulting calibration was probably not perfect but good enough to get a color noise free picture tested with some commercial video tapes.

I've never, in earnest , removed an individual head and fixed it to
another drum. If enough of the ferrite was remaining on the original I
would clamp the drum to a stout plate and manouevre a vinyl record
stylus tip adjascent to the gap in the ferrite and fix in place and
another such stylus on the other side, before undoing the screw holding
the brass in place. Then gently move the replacement head into position
and somehow clamp the brass to the drum before tightening the screw

 

[N_Cook]

went back to plan A as my temporary glue method failed to fransfer bits
of ferrite of sort of dimensions .5x,.3x.3mm.
Epoxy loaded with ferrite grinding dust, seemed to make a good bridge
bwetween gap and small coil, probably surface tension helping.
I will leave to cure until tomorrow but anyone know of an out of machine
rudimentary test for head functionality? Heads on their own ,
disconnected from rotary coil, rotating magnet? just so can try on each
head ,in turn, to compare responses

my repair did not work , so whatever turns up on ebay as "needs repair"
or even working order

 

[Jeroni Paul]

Back in ancient times when VHS machines has simple two head designs, A and B heads, I had two identical upper cylinders, natually one with a bad "A head" and the other with the "B head" broken and tried a transplant betweenthe two. Even having access to a brand new 3rd one and making multiple measurments of every x-y-z measurement I could make, it never worked.

I remember when I did this experiment I noticed both drums had a yellow head and a green head, the color surrounding the soldering pads. At first I thought that color identified the odd/even field head but to my surprise it did not, so after the transplant I ended with a working drum with two yellowheads.

I found that the second time I did the transplant because just like the first I did I was expecting it to work but it did not. While I was checking the ferrite with a magnifier I noticed the gap inclination of the head I installed was the same as the head already in the drum. The color in the head pads mislead me to take the wrong head from the donor drum.

 

[N_Cook]

I remember when I did this experiment I noticed both drums had a yellow head and a green head, the color surrounding the soldering pads. At first I thought that color identified the odd/even field head but to my surprise it did not, so after the transplant I ended with a working drum with two yellow heads.

I found that the second time I did the transplant because just like the first I did I was expecting it to work but it did not. While I was checking the ferrite with a magnifier I noticed the gap inclination of the head I installed was the same as the head already in the drum. The color in the head pads mislead me to take the wrong head from the donor drum.

Anyone know where to find the dimensional specs/standards of helical
scan systems (before wear anyway) particularly diameter between head
face surfaces and angular offsets , particularly for DAT and video8
systems?

 

[N_Cook]

my repair did not work , so whatever turns up on ebay as "needs repair"
or even working order

By not work, pre-recorded Bond movie on a DAT tape plays a useable B&W
image but absolutely no sound . In 6 chanel PCM audio mode no sound on
any of the 6 chanels of a tape with n6ch audio recorded to it