[TechAssist] Re: JVC VCR HR-J420U acts like bad heads- but is it?
- From: "peter kowalik" <pe.kow@xxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Fri, 9 May 2003 00:10:12 -0400
Wouldn't the head assembly and the AC head show greater wear from being
played in EP mode rather than SP. I always thought that the unit would
perform better in SP than EP since there would be less friction and the
transport mechanism would actually be working at the speed that it was
designed to work at. Isn't the speed that is used in EP achieved by lowering
the voltage to the motor thereby causing more drag across both the video
drum and the AC head? Am I wrong, please correct me if that is so. Thank
you all. Peter Kowalik pe.kow@xxxxxxxxxxxx Keith's Stereo burl ont
----- Original Message -----
From: <MDileo0000@xxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Thursday, May 08, 2003 11:19 AM
Subject: [TechAssist] Re: JVC VCR HR-J420U acts like bad heads- but is it?
>
> Gary,
>
> Bad heads for sure. The heads have worn back far enough to give marginal
> response. The envelope will round off at the entrance point because of the
> uneven wearing of the heads themselves. The leading, entrance, edge of the
> heads bear the brunt of the intial contact force as the heads rotate into
and
> against the tape, and subsequently wear faster.
> I would also look closely at the A/C head for grooving, which was a
common
> problem with these machines. If the customer used the vcr principally for
> rental playback and SP recording chances are good that the A/C head is
> marginal also. If the customer records at the EP speed exclusively, as
> working women who record and playback six hours of soaps a day, the A/C
head
> will only have endured a 1/3 as much wear.
>
> Dominic DiLeo
> Atlantic TV
> Freeport, Maine
> __________________________________________________
>
>
> I have this JVC VCR model HR-J420U which shows a few lines across the
> screen near the top during playback of some SP or EP speed tapes.
>
> Pulling the back tension post out further by hand would make the lines
> go away but adjusting the arms position with it's set screw would only
> result in a worse picture, never better.
>
> I scoped the RF envelope waveform and it didn't look very good, not
> square at all. I set the tracking to manual and tried to align guide
> posts so the envelope would be squared up. This seemed to work out ok
> using my test alignment tape, but some other factory made tapes still
> had the problem and some were even worse than before I made any
> adjustments. Actually the envelope waveform is now fluctuating. It won't
> stay the same shape while playing most tapes. It keeps gradually losing
> the signal from the one head and getting it back again slowly, while the
> other head goes from square waveform shape to oval shape. Hope I've
> explained this ok. The control pulse appears to be stable at approx. 3V
> p-p at C.P. test point, regardless of what tape I am playing.
>
> I removed the upper drum and checked for green corrosion at the base of
> the post as was a problem with some JVC machines a few years ago. All
> was clear. I also tried a new spring at the back tension arm but that
> didn't help either. This problem seems to be worse on EP speed tapes.
> Are my heads just too weak to lock in the RF signal or are there other
> known conditions with these machines causing this type of fault?
>
> Thanks for any help.
> --
>
>
>
>
> Gary McCartney
>
> McCartney Electronics
> 7134 Fife Rd, RR 7
> Guelph Ontario Canada N1H 6J4
> Fax: (519)821-1530
> email: gary (at) number63.ca
>
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