[TechAssist] Re: JVC VCR HR-J420U acts like bad heads- but is it?
- From: MDileo0000@xxxxxxx
- To: techassist@xxxxxxxxxxxxx
- Date: Thu, 8 May 2003 11:19:18 EDT
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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