Panasonic AG-1980 hi fi problems w/ new video head

[Robert K]

After replacing the upper cylinder unit in my Panasonic AG-1980,
now Hi Fi audio on SLP is not compatible with other VCRs, while picture
is perfect.

This unit uses the new GLDD type cylinder, which requires no soldering
and no screws removal. This is an original video head purchased from
a reputable Panasonic parts distributor and the packaging was perfectly
sealed.

I have an original service manual, but there is no indication of
any adjustment related to hi fi audio.

Does anybody have experience with this VCR and this situation?
How can I solve it? I am an engineer but I do not work in repairs,
this is my personal VCR.

I appreciate any input and feedback, or any attachment of schematics
if there is any manual supplements that relate to my problem
and that did not come with my original manual (purchased several years
ago).

Thanks in advance.

Robert K.

[JURB6006]

You probably need to reduce the YFM level, as in EP there is more depth
mutiplexing than sidestepping of the AFM signal. Thus the video is partially
erasing the audio due to a more efficient video head.

At one time there might have been some wear on the EP heads and someone may
have tweaked it to use the same heads longer.

There is also the possibility that the dihedral is off on the hifi heads, but
that's rare on OEM replacement heads. It's kinda tricky to tell if this is the
case, it involves watching both the video and audio envelopes on an EP tape.
Ideally on several tapes. It would be good to compare a tape made previously on
that machine (with the old head) to a newly made one. If this is the case there
is no way to adjust it, only the factory can do that. I've adjusted one in my
life, I was successful but it took all day, lots of trail and error. I would
not attempt it again. What's more this was not a Hifi unit, your's would be
much trickier. Even determining <u>if</u> this is the problem is kinda hairy.

Whatever the case you might be able to increase the AFM carrier level. This
might do the trick no matter what the problem is.

Before adjusting anything I would check alot of caps around the Hifi output
circuit (to the heads). YFM and AFM have to be precariously balanced during the
record mode, so if some of your electrolytics are drying out all you might have
to do is replace a bunch of them. The only reason I didn't mention this first
is because I got got the impression that the problem wasn't there before, and
now, all of the sudden it is there.

Did you replace the head due to simple wear or was there one bad head on the
drum (damaged maybe) or what ? This info might help figure this one out.

JURB

[Robert K]

Thanks for your help JURB6006.

This video head does not require soldering nor screws, I
just removed the old head and installed the new one.
I didn't touch the guidepost, but I checked the "envelope" TP
I found on the main board, and the tape alignment seems to be
perfect. The video quality is perfect, even when in SLP and going
through still, search, slow motion, etc.

I also performed some comparisons, as the old video head still works
just fine (I'm replacing it because the unit has around 2500/3000
hours without service maintenance). No matter what I check, everything
looks the same through the scope, and I can't believe the original
service manual I have, does not even mention anything related with FM
or Hi-Fi audio adjustment, nor audio Hi-Fi switching point ADJ, or any
off the typical audio Hi-Fi related ADJ I used to find in Hi-Fi VCRs
manuals that I remember seeing some years ago.

Every time I try installing the old head, the SLP audio
works just fine, and the unit becomes 100% compatible with
the other 3 S-VHS Hi-Fi VCRs I have (JVC, and two Mitsubishis).

With the brand new head, my AG-1980 has problems to
play the Hi-Fi audio of the SLP tapes it has just recorded.
Same problem occurs when playing these tapes on other VCRs.
It seems as if it was going out of tracking, but video remains perfect.

As the Video picture quality is perfect, the problem should be related
with the Audio switching point, or some sort of hard to measure
misalignment between the old and the new head. I can't believe the
original AG-1980 Panasonic service manual does not even mention
anything related with Hi-Fi audio ADJ. The manual shows just the PG
Shifter ADJ, S-VHS current ADJ, and others adjustment non related
with the Audio Hi-Fi, what lead me to believe that perhaps this newest
GLDD (Liquid Drive) heads used in the G-Mechanism, may be does not
required any ADJ at al when replaced?

When I purchased the AG-1980 original Service Manual some years
ago, it has the "AG-1980P / K-Mechanism" identification on it's cover,
and I also got the "K-Mechanism" manual, but there is not mention of
Audio Hi-Fi ADJ at all, and I'm wondering that perhaps there are other
newest or more specific Panasonic service guides or manuals that
indicate
the correct Audio Hi-Fi QADJs and procedures to fix problems such as
mine.

So far, it looks like I'm going to end in a Panasonic service dealer,
which I
tried to avoid only because it will take several days until I have it
back, and I
need to work with this particular VCR almost every day.

Thanks again.
Robert K.

"JURB6006" <jurb...@aol.com> wrote in message
news:20011217205458...@mb-cq.aol.com...