[TechAssist] Re: JVC TV AV2749S, yoke arcing at CRT neck [UPDATE 3]
- From: "teltek3" <teltek3@xxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Thu, 21 Aug 2003 11:57:15 -0400
Gary;
I'm not sure...but placing magnets on the tube should not change your
waveshape..maybe I'm wrong..If you can do it mechanically you should be OK.
-Ed-
-Ed-
Tel-Tek Electronics
Ontario-Canada
teltek3@xxxxxxxxxxxx
----- Original Message -----
From: "Gary McCartney" <gary@xxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Thursday, August 21, 2003 11:27 AM
Subject: [TechAssist] JVC TV AV2749S, yoke arcing at CRT neck [UPDATE 3]
> I am back working on this set again. Still trying to find a way to
> narrow the picture a bit, I am now in the pincushion area of the
> circuit. I have fastened a permanent magnet to the top of L523 which is
> in series with the horizontal yoke winding. L523 already has a magnet on
> it's top, and if I mount my own magnet to L523 in the attracting field,
> the picture goes wider. If I mount the magnet in the opposing field, the
> picture goes narrower to the amount I have been hoping for. Watching the
> HOT waveform while experimenting, I haven't seen it change in amplitude
> or in shape. I am now letting the set run for an hour so I can measure
> temperatures.
>
> Has anyone ever tried this type fix and is there any concerns to worry
> about, presuming the set runs as cool as it did previously?
>
>
>
>
> Gary McCartney
>
> McCartney Electronics
> Guelph Ontario Canada
> Est. 1984
> email: gary (at) number63.ca
>
>
>
>
>
> My previous messages:
>
>
>
> My update # 2:
>
> I have test run this set now, and after an hour's run, the HOT heatsink
> is at 44 deg. C and the regulator heatsink is at 55 deg. C. This is with
> either the original 0.0062 uF cap installed, or my 0.0051uF. With the
> original cap, the anode HV runs at 30kV zero beam current, and with the
> 0.0051 cap installed, the HV runs at 31kV.
>
> To me it seems 30kV is a bit high for a 27" tube. Is not 28kV more the
> morm? The label on the CRT doesn't state the level it should be at. All
> it says to not exceed the max. level.
>
> Can anyone tell me what the actual HV anode voltage should be on this
> set, and what I can do to lower it? I will post this question in a new
> thread also for those who haven't been following this thread.
>
>
> Thanks for any help.
>
>
>
>
>
>
>
>
>
>
>
> My previous update message:
>
>
>
> George, I tried a 0.0051 1600V and the picture narrowed by about 3/4"
> but the HOT collector waveform went from 1200V p-p (with original caps
> installed) to 1250 Vp-p. I have put the original cap back in to run the
> set for a while so I can measure the HOT temp. then I'll run it with the
> 0.0051uF and measure the temp.
>
> Is 1200V p-p too high for these JVC's? I think most TVs are 1050 to
> 1100V p-p.
>
>
>
>
>
> Gary McCartney
>
> McCartney Electronics
> Guelph Ontario Canada
> Est. 1984
> email: gary (at) number63.ca
>
>
>
>
> George wrote:
> >
> > Gary,
> >
> > Try an .005 for the .0062 to start and then you can go from there just
keep
> > an eye on the HV rise as you reduce the value to make sure that it
remains
> > within the limit.
> >
> > George
> > Afana Electronics
> > Moreno Valley, CA
> >
> > ----- Original Message -----
> > From: "Gary McCartney" <gary@xxxxxxxxxxx>
> > To: <techassist@xxxxxxxxxxxxx>
> > Sent: Friday, August 15, 2003 10:47 AM
> > Subject: [TechAssist] JVC TV AV2749S, yoke arcing at CRT neck [UPDATE]
> >
> > > I have this set running now. I applied epoxy to the spot on the glass
> > > and covered it with tape. I have a good picture except for one
problem.
> > > It has too much width, about 1 to 1 1/2 inches too much. The geometry
> > > look fine though. The used yoke I installed did not have a JVC number
on
> > > it and did not have the same connectors, but the yoke itself appeared
to
> > > be the exact same. I realize that even though it looked exact the
> > > winding could be slightly different.
> > > Assuming the new yoke is the same as the old, I have removed the 2
blue
> > > caps C525 and C524 from the HOT collector to ground. Can anyone
identify
> > > the valuse of these caps please?
> > >
> > > C524: labelled PH7001H 1.6KV
> > > C525: labelled PH6201H 1.6KV
> > >
> > > I believe these are 0.007uF and 0.0062uF but I'd like this confirmed
if
> > > possible.
> > > SAMS is having techical problems with their web site else I'd look up
> > > the SAMS number for this set.
> > >
> > > What else can cause too much width in this chassis? Is it safe to
change
> > > the value of one of these caps enough to narrow the picture up a bit?
I
> > > am concerned that perhaps the yoke burnt in the first place because of
> > > to much current going through it.
> > >
> > >
> > > Thanks for any help.
> > >
> > >
> > >
> > >
> > > Gary McCartney
> > >
> > > McCartney Electronics
> > > Guelph Ontario Canada
> > > Est. 1984
> > > email: gary (at) number63.ca
> > >
> > >
> > >
> > >
> > >
> > >
> > > My Original message:
> > >
> > >
> > > I have this JVC TV model AV2749S in the shop and I have found that
the
> > > yoke is shorted where it wraps around the neck of the CRT, causing a
> > > black burn mark on the glass. I took a knife and scraped it off but
> > > there is a slight crater in the glass now, maybe 1/64 of an inch or so
> > > deep. Is this a weak spot from now on, meaning that this spot will be
> > > suseptable to more arcing in the future or worse yet, a crack in the
> > > neck? Can I apply some epoxy to the spot to give it insulation, or
> > > should this tube be scrapped? I have a used yoke which looks to be in
> > > great shape which I can use in the set so I hate to tell the customer
it
> > > is garbage.
> > >
> > >
> > > Here is a photo of the mentioned spot on the glass:
> > >
> > > http://www.number63.ca/tube-neck.jpg
> > >
> > >
> > >
> > > How I found the bad yoke:
> > >
> > > The set came in with F902, 1.25 Amp fuse open. I couldn't find any
> > > defective parts so I installed a new fuse in case that was the only
> > > problem. Pressed power button and saw LED blink and that was all- the
> > > fuse was open again. Next, I looked up tips and found one that
mentioned
> > > the yoke as a possibility, so I pulled the CRT board and the yoke
> > > connectors. The LED came on and stayed. Then I reconnected the hor.
> > > winding and put a new fuse in. Had to use 1.5A instead of 1.25. I used
a
> > > variac set at 90VAC and plugged it in. The LED came on and I heard the
> > > arcing and saw smoke coming from the yoke/ CRT neck.
> > >
> > >
> > > Thanks for any help.
> > > --
> > >
> > >
> > >
> > >
> > >
> > >
> >
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