View Full Version : CRT Issues


Outland
01-18-2016, 02:13 AM
I've been seeing two problems on a 1994 BPC Panasonic set I have.

The first is a bending of the top few lines of an image.

http://i1052.photobucket.com/albums/s451/apples555/IMG_0626_zpso4pjtgsj.jpg

The other is an impression of an image to the right of anything bright or shiny.

http://i1052.photobucket.com/albums/s451/apples555/IMG_0652_zpsxfgvfwql.jpg

http://i1052.photobucket.com/albums/s451/apples555/IMG_0648_zps82nskgkw.jpg

http://i1052.photobucket.com/albums/s451/apples555/IMG_0644_zps29qkp1xu.jpg

Is this a CRT issue or something repairable?

ChrisW6ATV
01-18-2016, 02:36 AM
Not CRT issues, in my experience. The bending may just be a horizontal-hold/frequency adjustment internally. Did you have this set working without these issues in the past, or did you get it this way?

Outland
01-18-2016, 02:42 AM
I think the shadows to the right weren't there before. Not sure about the bending.

The set had an issue with a bad joint in the vertical IC that would compress the picture periodically. A whack also temporarily fixed it.

Ed in Tx
01-18-2016, 08:48 AM
edit.. delete after re-looking at the pic, top looks like a bit of "flagging" used to be common with VCR playback and certain TVs. Horizontal timing I recall was the issue.

ChrisW6ATV
01-18-2016, 01:38 PM
Do all video sources show the bending? Is the ghosting/ringing equal with composite-video as well as S-video and RF inputs? It could be something like loose grounding/shielding or wiring in the video circuits.

Outland
01-18-2016, 11:09 PM
The bending doesn't happen on all sources, as far as I can tell. The ghosting does happen with all sources though. Capacitors?

ChrisW6ATV
01-19-2016, 05:00 PM
Yes, bad ones in the video circuits could cause that. I would expect to use an oscilloscope and trace input signals through the set at this point.

old_tv_nut
01-19-2016, 06:23 PM
All sets can show a little bending at the very top with VCR playback, even those designed after VCRs came into use. It will vary with different tapes and VCRs. If it is within the first few percent of the raster, just turn up the height a little to hide it off the top of the screen. If it extends very far from the top, check the capacitors and resistors in the horizontal AFC section.

Electronic M
01-19-2016, 06:38 PM
All sets can show a little bending at the very top with VCR playback, even those designed after VCRs came into use. It will vary with different tapes and VCRs. If it is within the first few percent of the raster, just turn up the height a little to hide it off the top of the screen. If it extends very far from the top, check the capacitors and resistors in the horizontal AFC section.

You could also put a TBC between the VCR and the TV to fix the VCR signal so that it no longer causes bending.

Outland
01-19-2016, 07:28 PM
It happens with DVDs too. Is the ghosting bad caps too?

Username1
01-19-2016, 07:32 PM
I have a couple of late Panasonic tv's and they have a number of bad solder joints
that have caused all kinds of strange behavior. One of them had bad connections
along the tuner, kind of a unit by itself, lots of bad connections caused a lot of the
poor definition I see in your pictures, especially the "stop" Picture. If not all devices
have the bad look, then you might have to look into the impedance matching
transformer and the other stuff inside the tuner near the input.

.

Outland
01-19-2016, 07:56 PM
How can I start diagnosing/working on the problem?

EDIT: There's only one input, the coaxial RF.

ChrisW6ATV
01-19-2016, 09:52 PM
If there is only an RF input, a small amount of that kind of ghosting on fine details may be normal; also, any set made in 1994 with only an RF input is by definition a low-end set, so again it will not have the picture quality of higher-line sets.

ChrisW6ATV
01-19-2016, 09:54 PM
If it was my set, I would look inside for the horizontal-hold/frequency adjustment and try tweaking it, and not worry about the ghosting at all.

Outland
01-20-2016, 04:46 AM
Noted, I'll do that.

Thanks all.

andy
01-20-2016, 11:24 AM
If there is only an RF input, a small amount of that kind of ghosting on fine details may be normal; also, any set made in 1994 with only an RF input is by definition a low-end set, so again it will not have the picture quality of higher-line sets.

I agree that it doesn't look that bad. When you examine the picture of most NTSC CRTs under a microscope, you'll see all kinds of problems such as minor ghosting. They just weren't designed to look perfect for sharp text like that. If it's not noticeable from a normal viewing distance when looking at normal video content, I'd say it's working fine. If you want pixel perfect accuracy, then get a flat panel and feed it from a digital source...

Outland
01-20-2016, 10:52 PM
It's somewhat noticeable, particularly with a red shirt bleeding a little more right than left. That said, expecting Trinitron quality from a low-end Panasonic might be the core of the problem here.

There's also a little burn-in from closed captioning, so it's not like the ghosting is the only problem standing in the way.