[TechAssist] Re: JVC TV AV2749S, yoke arcing at CRT neck [UPDATE 2]
- From: Gary McCartney <gary@xxxxxxxxxxx>
- To: techassist@xxxxxxxxxxxxx
- Date: Mon, 18 Aug 2003 09:58:43 -0400
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.
Gary McCartney
McCartney Electronics
Guelph Ontario Canada
Est. 1984
email: gary (at) number63.ca
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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