DAT "video" head replacement?

[Gareth Magennis]

"dave" wrote in message
news:6-qdnYMaLabErrPPnZ2dnUVZ_qydnZ2d@earthlink.com...

On 09/09/2013 11:10 AM, Gareth Magennis wrote:

Those are contacts, not the head gaps. Where is your "black sludge"
coming from?




You are not making a lot of sense.
Both VCR and DAT heads get dirty, black stuff comes off them when you
clean them, then they work properly again.

Seriously, the only "stuff" you should see is maybe some shedding from
cheap tape, usually more brown than icky black. Do you have a lot of
smokers around?



Look, if you had bothered to read this thread properly you would know I used
to repair DAT machines for a living.

I know what it is to clean a dirty head, and I know what the results of
doing so is. I have done this a lot.

Clearly you haven't, but instead have probably destroyed a couple of heads
by cleaning them with a Q-tip, and then come to the perverse conclusion that
cleaning DAT heads does not work.




Gareth.

 

[Cydrome Leader]

dave <ricketzz@earthlink.net> wrote:

On 09/07/2013 04:19 AM, N_Cook wrote:
I've decided , when I get back to it , to drill matching 8 holes in a
plate and hope 8x 1mm screws, 5 threads each, will hold in place while
trying to separate the 2 drums

It has been my experience that once you start cleaning a rotary head
with qtips and alcohol the head is gone. If the '"dirty up" brush, then

qtips on flying heads is always bad news. They'll snag and shed. I've
always used acetone and plain paper for cleaning such heads. It works
great.

qtips and acetone for the path and capstan and pinch roller. A soft dull
screwdriver tip can scape edge of the tape crud off a capstan.

Some heads (well the drums) looks pristeen but no longer function. Some
cruddy looking ones still work fine. Anyways, if the cover comes off,
everything gets cleaned.

a cleaning tape, won't clear things the head is gone. It is not
cost-effective to replace. You can buy an SSD based recorder/player for
way less than the cost of a new drum.

Somebody want want to play back some dat tapes. In the video world,
cleaning tapes are pretty pointless as they can't clean the path.

 

[dave]

On 09/09/2013 02:35 PM, Gareth Magennis wrote:

"dave" wrote in message
news:6-qdnYMaLabErrPPnZ2dnUVZ_qydnZ2d@earthlink.com...

On 09/09/2013 11:10 AM, Gareth Magennis wrote:


Those are contacts, not the head gaps. Where is your "black sludge"
coming from?




You are not making a lot of sense.
Both VCR and DAT heads get dirty, black stuff comes off them when you
clean them, then they work properly again.


Seriously, the only "stuff" you should see is maybe some shedding from
cheap tape, usually more brown than icky black. Do you have a lot of
smokers around?



Look, if you had bothered to read this thread properly you would know I
used to repair DAT machines for a living.

I know what it is to clean a dirty head, and I know what the results of
doing so is. I have done this a lot.

Clearly you haven't, but instead have probably destroyed a couple of
heads by cleaning them with a Q-tip, and then come to the perverse
conclusion that cleaning DAT heads does not work.




Gareth.

Usually I used a chamois swab and a fluid especially made for head
cleaning. But, running a large fleet of helical scanning VCRs and DVRs
(BetaCam, U-matic, Panasonic M, DigiBeta, you name it); we found the #1
policy to keep the heads clean is to forbid the use of certain brands of
tape and to keep food out of the machine areas. Black grease indeed.

 

[N_Cook]

7x 1mm screws with little washers and pads of silicone under the heads,
through holes in a plate with a reaction frame fitted, and screwed to
the DAT drum. 40 seconds of low heat hot air and the circlip pliers as a
lever and the bottom drum came away. Leaving the ball race on the drive
and the drum separating from the outer section of the race. Upper
ferrite former for thre upper coupling coil seems to be glued to the
central lump. Desoldered at the 4 solder joins but not yet tried heating
the ferrite to see if it comes away. Under that is the head mount
screws. The heads are about 80% the size of VHS heads, and certainly
thinner, will have to find a scrapped 8mm set of heads

 

[Gareth Magennis]

"N_Cook" wrote in message news:l0qc8u$7rt$1@dont-email.me...

7x 1mm screws with little washers and pads of silicone under the heads,
through holes in a plate with a reaction frame fitted, and screwed to
the DAT drum. 40 seconds of low heat hot air and the circlip pliers as a
lever and the bottom drum came away. Leaving the ball race on the drive
and the drum separating from the outer section of the race. Upper
ferrite former for thre upper coupling coil seems to be glued to the
central lump. Desoldered at the 4 solder joins but not yet tried heating
the ferrite to see if it comes away. Under that is the head mount
screws. The heads are about 80% the size of VHS heads, and certainly
thinner, will have to find a scrapped 8mm set of heads



VHS heads and DAT heads do not perform the exact same physical task.

You need to research this properly, but AFAIK, VHS heads record stripes of
data with blank "guard tracks" in between, so adjacent tracks do not
interfere with each other (being as the system is analogue).

DAT head tracks actually overlap each other, so there is never any piece of
tape with no signal on it.

Meaning the size of the heads in relation to the spacing of the track are
not the same for both formats.


This is important in DATs, because the ATF system, which keeps the head in
the centre of the track, needs to be able to read, via the playback head,
both adjacent tracks' ATF signals simultaneously.
Since tracks overlap, it is able to do this playing back a single track.
If one is lower amplitude than the other, the system will alter tracking to
make them the same, thus ensuring the head is travelling dead centre down
the track.

VHS systems do none of this.



This is all from a 10 year memory, and I haven't bothered to check any of
it, but I believe this is basically the case.
I don't mind being proved wrong.



(I'm not sure whether your above post is considering substituting some other
format head for the DAT head, hence this "heads up" post)



Gareth.

 

[Gareth Magennis]

"N_Cook" wrote in message news:l0qc8u$7rt$1@dont-email.me...

7x 1mm screws with little washers and pads of silicone under the heads,
through holes in a plate with a reaction frame fitted, and screwed to
the DAT drum. 40 seconds of low heat hot air and the circlip pliers as a
lever and the bottom drum came away. Leaving the ball race on the drive
and the drum separating from the outer section of the race. Upper
ferrite former for thre upper coupling coil seems to be glued to the
central lump. Desoldered at the 4 solder joins but not yet tried heating
the ferrite to see if it comes away. Under that is the head mount
screws. The heads are about 80% the size of VHS heads, and certainly
thinner, will have to find a scrapped 8mm set of heads



Oops, just realised you might be talking about 8mm camcorder heads?


Anyway, the same research heads up applies.


Gareth.

 

[William Sommerwerck]

To the best of my knowledge, this is not correct. VHS has little or no gap
between the stripes, nor does Betamax. That's what "Betamax" refers to --
maximum surface coverage, "bet" being the Japanese word for surface coverage.

Because the luminance signal is FM, a bit of leakage causes no harm, as the FM
capture effect can be used to eliminate it, by limiting the signal. The
chrominance signal is AM, and an alternating- or rotating-phase carrier is
used to minimize crosstalk.

 

[Gareth Magennis]

"William Sommerwerck" wrote in message news:l0qiot$ge2$1@dont-email.me...

To the best of my knowledge, this is not correct. VHS has little or no gap
between the stripes, nor does Betamax. That's what "Betamax" refers to --
maximum surface coverage, "bet" being the Japanese word for surface
coverage.

Because the luminance signal is FM, a bit of leakage causes no harm, as the
FM
capture effect can be used to eliminate it, by limiting the signal. The
chrominance signal is AM, and an alternating- or rotating-phase carrier is
used to minimize crosstalk.



Well, I might have to do a bit of Googling then, I've never been involved
much with video.

The main difference is, I believe, that DAT kind of reads 3 tracks at once,
video doesn't, thus head size is critical if considering some kind of head
substitution.



Gareth.

 

The ATS must work the same way it did in the 8 mm. video decks. In them, there are four rotating frequencies used. The primary on track frequency is the strongest coming out of the head, two other frequencies are expected at lower levels. The capstan motor is adjusted by the servo to equalize the two off track frequencies.

At each pass of the head it uses a different frequecy for the on track frequency and of course it expects two other frequencies just the same as last time.

There are four frequencies and the reason for that rather than just three is to keep it from getting confused. When F1 is recieved it KNOWS it is looking for F2 and F4 for example, then when F2 is on track it looks for F1 and F3, then when it goes to F3 it looks for ........ I forget. It doesn't matter, but this should illustrate the reason to use four frequencies rather than only three. It assures the proper operation of the servo because there can be no mistake about which track is leading the "on" track and which is lagging.

This system eliminates the need for a control head and errors introduced due to tape stretching. The 8 mm. decks did actually usually have a sub audio head but I doubt it was ever used except maybe in some super cheapo deck which didn't even make it to market. It may have been used for a tape counter as well, I simply don't remember those details.

Interestingly there were decks that used the 8 mm. tape strictly for audio. The tape wrap was actually greater than 180 degrees and one sector was used for digital audio tracks. These were not the greatest format in the world but they beat BTSC and were good enough for music, as in better than most cassettes. The 8 mm. decks with the feature to go all audio simply used more sectors for more digital all audio mode. If you recorded say tracks 5 and 6 on a tape that had video on it you would see a band across the screen where the new audio tracks were recorded. The system also had the drawback of having to completely rewind before playing the subsequent tracks.

Needless to say these things did not get a huge market share. I just know about them because I worked for a high end Sony dealer.

This is completely different than the auto tracking feature in any VHS deck and I am unaware of automatic tracking being incorporated in any Beta deck, though I might not have seen them all.

Additionally, in the DAT formet I don't know, and I simply don't remember on the 8 mm. decks if the actually recording carrier frequency was rotated or if they were like "pilot" frequencies simply chosen not to interfere with the signal, but it really doesn't matter. That's how such a system works.

 

[William Sommerwerck]

"Gareth Magennis" wrote in message news:Fy4Yt.42772$H%2.175@fx16.am4...

The main difference is, I believe, that DAT kind of reads 3 tracks at once,
video doesn't, thus head size is critical if considering some kind of head
substitution.

I don't think that's true -- how would you separate the tracks? But I'd better
not "take sides".

I do know that some decks have two heads -- rather than one. This allows
off-the tape monitoring, just as in three-head analog deck -- at the expense
of greater tape wear.

 

[Gareth Magennis]

"William Sommerwerck" wrote in message news:l0qutd$k0i$1@dont-email.me...

"Gareth Magennis" wrote in message news:Fy4Yt.42772$H%2.175@fx16.am4...

The main difference is, I believe, that DAT kind of reads 3 tracks at
once, video doesn't, thus head size is critical if considering some kind
of head substitution.

I don't think that's true -- how would you separate the tracks? But I'd
better
not "take sides".

I do know that some decks have two heads -- rather than one. This allows
off-the tape monitoring, just as in three-head analog deck -- at the expense
of greater tape wear.




You need to do some research on the way DAT works.

It is not what is currently in your head.


Gareth.

 

[William Sommerwerck]

"Gareth Magennis" wrote in message news:7m7Yt.64150$Gn7.17824@fx22.am4...
"William Sommerwerck" wrote in message news:l0qutd$k0i$1@dont-email.me...

The main difference is, I believe, that DAT kind of reads 3 tracks
at once...

Kind of?

You need to do some research on the way DAT works.
It is not what is currently in your head.

Then point me to a reference. Virtually all of the online material is in SMPTE
or AES articles, which you cannot access for free.

 

[Gareth Magennis]

wrote in message
news:67f516e0-6c29-47e4-a430-d299d330e210@googlegroups.com...

The ATS must work the same way it did in the 8 mm. video decks. In them,
there are four rotating frequencies used. The primary on track frequency is
the strongest coming out of the head, two other frequencies are expected at
lower levels. The capstan motor is adjusted by the servo to equalize the two
off track frequencies.

At each pass of the head it uses a different frequecy for the on track
frequency and of course it expects two other frequencies just the same as
last time.

There are four frequencies and the reason for that rather than just three is
to keep it from getting confused. When F1 is recieved it KNOWS it is looking
for F2 and F4 for example, then when F2 is on track it looks for F1 and F3,
then when it goes to F3 it looks for ........ I forget. It doesn't matter,
but this should illustrate the reason to use four frequencies rather than
only three. It assures the proper operation of the servo because there can
be no mistake about which track is leading the "on" track and which is
lagging.

This system eliminates the need for a control head and errors introduced due
to tape stretching. The 8 mm. decks did actually usually have a sub audio
head but I doubt it was ever used except maybe in some super cheapo deck
which didn't even make it to market. It may have been used for a tape
counter as well, I simply don't remember those details.

Interestingly there were decks that used the 8 mm. tape strictly for audio.
The tape wrap was actually greater than 180 degrees and one sector was used
for digital audio tracks. These were not the greatest format in the world
but they beat BTSC and were good enough for music, as in better than most
cassettes. The 8 mm. decks with the feature to go all audio simply used more
sectors for more digital all audio mode. If you recorded say tracks 5 and 6
on a tape that had video on it you would see a band across the screen where
the new audio tracks were recorded. The system also had the drawback of
having to completely rewind before playing the subsequent tracks.

Needless to say these things did not get a huge market share. I just know
about them because I worked for a high end Sony dealer.

This is completely different than the auto tracking feature in any VHS deck
and I am unaware of automatic tracking being incorporated in any Beta deck,
though I might not have seen them all.

Additionally, in the DAT formet I don't know, and I simply don't remember on
the 8 mm. decks if the actually recording carrier frequency was rotated or
if they were like "pilot" frequencies simply chosen not to interfere with
the signal, but it really doesn't matter. That's how such a system works.







There's another thing I've just remembered after sleeping - DAT heads were
offset with regards to azimuth, i.e. head A was set at a very different
azimuth to head B, which made it easy to separate certain frequencies
intended for one particular head.


Gareth.

 

[Gareth Magennis]

There's another thing I've just remembered after sleeping - DAT heads were
offset with regards to azimuth, i.e. head A was set at a very different
azimuth to head B, which made it easy to separate certain frequencies
intended for one particular head.






And also, I believe it is possible to lose one head output altogether and
still recover 100% of the data, so presumably the ATF would still work on
one head.
Quite an interesting system, very different to VHS.

(Obviously any tape dropouts or other errors would not be able to be
corrected and would result in a glitch)



Gareth.

 

[N_Cook]

Here is a rare beast, pics of innards of a DAT drum
http://www.diverse.4mg.com/DAT.jpg
top views at top, 1mm squared paper and one of the 1mm screws I used.
The ring of white dots in image lower1 is where the middle ferrite disc
was superglued? to the central boss. I tried 20 seconds of 300 deg C
heat and trying to break the bond with a screwdriver blade, cracked the
ferrite, so the splodges are my superglue additions. 30 seconds of heat
and a smell of varnish or something and the bond broke.

 

[Gareth Magennis]

"Gareth Magennis" <gareth.magennis@ntlworld.com> wrote in message
news:sjeYt.64579$Ta4.55037@fx10.am4...

There's another thing I've just remembered after sleeping - DAT heads were
offset with regards to azimuth, i.e. head A was set at a very different
azimuth to head B, which made it easy to separate certain frequencies
intended for one particular head.






And also, I believe it is possible to lose one head output altogether and
still recover 100% of the data, so presumably the ATF would still work on
one head.
Quite an interesting system, very different to VHS.

(Obviously any tape dropouts or other errors would not be able to be
corrected and would result in a glitch)



Gareth.

And just one more thing, the Alignment Tapes required to align the tape path
I believe were specially recorded with no ATF signals, so the machine to be
aligned would free run.

So it is not possible to make your own alignment tapes using a known good
machine.

I'm sure theres a load more info I've forgotten, and probably quite a few
bits in this thread I have got wrong, but I don't have time to Google the
data as I have broken things to fix instead.

(It is at least 10 years since I actually repaired a DAT)



Cheers,

Gareth.



Gareth.

 

[N_Cook]

I forgot to include the motor section in those pics
I raided an 8mm video head drum. Heads about .2mm thicker (with the pcb
sliver) than DAT ones ,probably room , width 0.9mm wider , probably room
wit a chamfer on either side. Radial depth would need 3mm cutting off
and the fitting hole moved but as no precision there, probably feasible.
Strange, I've never removed an individual video head. I always wondered
how the head-coil ferrite could be mounted with epoxy on the brass
section with any precision. Now I see they use shims under the brass.
The one I looked at marked 76 , presumably 76 microns. I always thought
the mounting surface was a reference plane but not so, each head must be
assigned a shim , on test, before fitting. No idea whether 8mm and DAT
use the same reference plane and no idea how to set the video heads
before screwing down in place. When I have time I may have a go at
adapting and trying

 

"And just one more thing, the Alignment Tapes required to align the tape path
I believe were specially recorded with no ATF signals,"

OK, so they were separate frequencies, not the carriers.

However the lack of ATF signals is not required to align the deck. You still just align it, although you might confuse the system.

Most likely with a print you can find a way to disable the ATF system altogether, even if you have to disconnect the output from the heads. Believe me it can be done and should be done on a customer tape recorded previously in that machine, partly because compatability with other machines is not likely to be a big issue. For alignment I would get the tape tension as low as possible.

You know they said you needed all this equipment to align the old VHS recorders that had pots for the FM deviation and frequency and all that shit. Know what I did ? I just coupled the record signal to a deck "playing" a blank tape and "tuned it in". There is almost always a way, and remember, they are in business to make money.

This is digital so it is nowhere nearly as critical. Just get a good envelope out of it and it will be fine.

 

>"I forgot to include the motor section in those pics "

Yeah well the whole URL didn't work for me so it is no big deal on this end.

You should be able to do this without an alignment tape and all this shit, but I would not go drilling holes in it

 

[N_Cook]

On 13/09/2013 06:05, jurb6006@gmail.com wrote:
> they are in business to make money.

I have to wonder why they did not make the heads disc easily removable
like a video recorder and ,so, if there was a cheap and cheerfull
generic way of replacing the innards of "over a barrel" company-supplied
drums