question about CRT televisions
question about CRT televisions
when i turn my tv on there is a single horizontal line of video; it looks like the vertical trace has gone out. whenever i hit the ground near the tv the picture looks normal and then goes back to the single line again. im guessing this is a problem with the tube and is not really fixable?
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Chris Smith
- Posts: 4325
- Joined: Tue Dec 04, 2001 1:01 am
- Location: Bieber Ca.
Could be a bad ground in one of the traces?
Check all the circiut boards for a bad trace, but discharge everything before you start.
A highly insulated resistor wire [500/1000 ohms?] to a ground wire, to the frame and to absolute ground. Unplug the box first?
Use gloves as necessary?
Touch every thing you intend to get near, first.
Check all the circiut boards for a bad trace, but discharge everything before you start.
A highly insulated resistor wire [500/1000 ohms?] to a ground wire, to the frame and to absolute ground. Unplug the box first?
Use gloves as necessary?
Touch every thing you intend to get near, first.
With only this tech background / expertise info:
http://www.servomagazine.com/forum/sear ... hor=cinema
Now, do we really want to tell you which large red wire to firmly grasp with your left hand while plugging the set in with your right hand?
Elementary....... loss of vertical sweep or its power sourcing is your problem. Any simpler / nicer / cheaper problem would be a mere loss of sound!
Since you mentioned mechanical sensitivity:
It may be just as simple as a "floating lead" on the vert deflection IC. Tap on / around it ....with a plastic / phenolic insulative rod....while viewing the picture..
Coming back with your sets brand and model could get you some help, otherwise its impinging upon being a research impossibility.
73's de Edd
[email protected] ..........(Interstellar ~~~~Warp~~~Speed)
[email protected]........(Firewalled*Spam*Cookies*Crumbs)
.....Beat the 5 O'clock rush, leave work at noon!
.
http://www.servomagazine.com/forum/sear ... hor=cinema
Now, do we really want to tell you which large red wire to firmly grasp with your left hand while plugging the set in with your right hand?
Elementary....... loss of vertical sweep or its power sourcing is your problem. Any simpler / nicer / cheaper problem would be a mere loss of sound!
Since you mentioned mechanical sensitivity:
It may be just as simple as a "floating lead" on the vert deflection IC. Tap on / around it ....with a plastic / phenolic insulative rod....while viewing the picture..
Coming back with your sets brand and model could get you some help, otherwise its impinging upon being a research impossibility.
73's de Edd
[email protected] ..........(Interstellar ~~~~Warp~~~Speed)
[email protected]........(Firewalled*Spam*Cookies*Crumbs)
.....Beat the 5 O'clock rush, leave work at noon!.
heeheeRe: question about CRT televisions
could also be a loose or corroded connector to the deflection coils.cinema wrote:when i turn my tv on there is a single horizontal line of video; it looks like the vertical trace has gone out. whenever i hit the ground near the tv the picture looks normal and then goes back to the single line again. im guessing this is a problem with the tube and is not really fixable?
one flat line in the center means "no vertical deflection". Could be a lot. That you can vibrate it and make it work says it's fixable. But it's more than quite dangerous to arrange the power to operate the TV with the back open so you can tap here and there to isolate.
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Chris Smith
- Posts: 4325
- Joined: Tue Dec 04, 2001 1:01 am
- Location: Bieber Ca.
Cold solder joint somewhere. Or loose connection on deflection yoke. Possibly even an unsoldered wire on the yoke.
Take the back off the set.
Place mirror in front of set so you can see the screen.
Get a plastic stick of some sort. The longer the better. Made COMPLETELY of plastic. Use something like a kitchen serving spoon if you must. Something long and insulated that will keep your hand from touching anything and will not short two parts together.
Put a hand in yor back pocket. Plug in set. Power on set.
LIGHTLY tap various parts of the set, paying close attention to the magnetic coils around the CRT. Follow the wires from the CRT yoke down to the main board. Tap there. Tap the transistors and ICs and possibly capacitors and resistors near the wires from the yoke. My guess is you will find a bad solder connection or possibly a resistor that is opening.
When you localize the fault, switch to something like a ball point pen (with the cap on) to probe to the exact spot of the failure.
Cold solder joints can look one of two major ways. One, the solder is a dull shine to it instead of a bright shiny connection. Another type will have a hair line crack around the connection.
I've fixed CRT yoke problems where there was NO solder on the connections. The wire was hooked through the terminal connection, and heat shrink tubing was placed around the connection. The wire was held in place by the tubing only.
Another problem can occur with the connector. If the wire was not fully seated into the header, it may work its way out of the connector. Check for this at the main board.
Take the back off the set.
Place mirror in front of set so you can see the screen.
Get a plastic stick of some sort. The longer the better. Made COMPLETELY of plastic. Use something like a kitchen serving spoon if you must. Something long and insulated that will keep your hand from touching anything and will not short two parts together.
Put a hand in yor back pocket. Plug in set. Power on set.
LIGHTLY tap various parts of the set, paying close attention to the magnetic coils around the CRT. Follow the wires from the CRT yoke down to the main board. Tap there. Tap the transistors and ICs and possibly capacitors and resistors near the wires from the yoke. My guess is you will find a bad solder connection or possibly a resistor that is opening.
When you localize the fault, switch to something like a ball point pen (with the cap on) to probe to the exact spot of the failure.
Cold solder joints can look one of two major ways. One, the solder is a dull shine to it instead of a bright shiny connection. Another type will have a hair line crack around the connection.
I've fixed CRT yoke problems where there was NO solder on the connections. The wire was hooked through the terminal connection, and heat shrink tubing was placed around the connection. The wire was held in place by the tubing only.
Another problem can occur with the connector. If the wire was not fully seated into the header, it may work its way out of the connector. Check for this at the main board.
No trees were harmed in the creation of this message. But billions of electrons, photons, and electromagnetic waves were terribly inconvenienced!
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Robert Reed
- Posts: 2277
- Joined: Wed Nov 24, 2004 1:01 am
- Location: ASHTABULA,OHIO
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Tapping various locations to search for intermittents has its problems. Intermittent connections dont seem to follow a common sense pattern, especially at the board level. I have seen many times where a solid whack made no change and conversly, the softest of taps would consistently show the problem. The shock waves created by tapping can telegraph far upsteram or down steam from where you are tapping, getting into the intermittent that is actually in another location, and thus giving you the false impression that is occurring at the tapping point.
Follow Jolly Rogers set up with the mirrors and safety precautions, but before you start "rapping" away on the circuits, set up a monitoring point. A good stater would be the vertical amp output. Now when you see the trace appear, dissapear you can view it on the monitor (o-Scope is best) and know which direction to go for the next monitor point. By homing in on this, eventually you will get the monitor and intermitent to agree at only one location. It may sound like more work, but is actually a much faster troubleshooting technique. Some times one or two monitoring points and you have got it.
Follow Jolly Rogers set up with the mirrors and safety precautions, but before you start "rapping" away on the circuits, set up a monitoring point. A good stater would be the vertical amp output. Now when you see the trace appear, dissapear you can view it on the monitor (o-Scope is best) and know which direction to go for the next monitor point. By homing in on this, eventually you will get the monitor and intermitent to agree at only one location. It may sound like more work, but is actually a much faster troubleshooting technique. Some times one or two monitoring points and you have got it.
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radionut8888
- Posts: 8
- Joined: Mon Jul 17, 2006 11:13 am
- Location: Redding, CA
- Contact:
Vertical deflection
The vertical trace is usually magnetically generated by a set of coils around the base of the neck of the crt (as is the horizontal deflection).
Your symptoms point to an intermittent wire, connection at the deflection coil, or a bad trace/connection at the pcb. Usually, the horizontal trace experiences these failures, because there's more power expended in the horizontal circuit and thus more heat
That you still have a trace says the crt, horizontral trace and high voltage are probably OK. Tey running the TV and poke at the coil wires carefully with an INSULATED stick. If you can cause the trace to come and co, you'll narrow down the problem.
Your symptoms point to an intermittent wire, connection at the deflection coil, or a bad trace/connection at the pcb. Usually, the horizontal trace experiences these failures, because there's more power expended in the horizontal circuit and thus more heat
That you still have a trace says the crt, horizontral trace and high voltage are probably OK. Tey running the TV and poke at the coil wires carefully with an INSULATED stick. If you can cause the trace to come and co, you'll narrow down the problem.
Simple answer
Almost has to be a loose connection somewhere. This is very common on many TVs and is usually at the vertical output IC. If you give us the brand and model number it'll be easier to give you the most likely cause.
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