Old school TV problem

Harassed Dad · 28-09-2007, 09:00

We've got a widescreen JVC 32" CRT that has run well over a number of years, but has an increasingly regular intermittent fault. For some reason, occasionally when you turn the TV on the bottom left hand corner of the screen has a blue glow in a crescent shape radiating from the corner, where the blue is most intense. Doesn't happen all the time, and is more noticeable when watching sport (blue grass in that area). It's happened a few times when not watching sport as well, lastly giving a few of the characters in Corrie a worse skin tone than they normally sport.

Any ideas what is going on and is it fixable? Am loathed to change the TV as it works fine most of the time, and we have 2 young boys who haven't yet grown out of the sticky handprints on the screen phase, so a glass screen is a bonus at the moment.

broadz · 28-09-2007, 09:43

Tints in one corner of the screen are often caused by a magnetic field being given off by something near that particular corner, particularly speakers. Do you have a stereo surround sound system, and has the speaker nearest that corner of the screen been moved closer to the screen?

Harassed Dad · 29-09-2007, 14:13

Good thought - think I can discount it though, for the following reasons:

1) Fault is intermittent, and doesn't relate to speaker usage/sound volume.

2) Fault has remained in the same location despite 3 different houses and 2 different speaker systems.

3) The speaker on the right of the screen is a little closer in the current set-up (still over 12" away).

4) Speakers are on stands, and level with the top of the TV screen, not the bottom corner where the colour occurs.

Setup is a JVC 32" widescreen CRT TV, on a glass fronted wooden TV stand. In the cabinet, top to bottom are a Sony amp, Sky+ box and Sony HDD/DVD recorder. Speakers are Elac Cinema 1s, with the sub to the rear of the stand. Closest speaker is the centre one, stood on top of the TV. Previous speakers were Technics, with a larger centre speaker that also stood on top of the TV with no problems. TV speakers are switched off (via the JVC menu system) and the surround system is on whenever the TV is on.

Etaoin · 29-09-2007, 14:32

Does it disappear when the set is switched completely off (not just to standby) and then on again?

Switching off completely degausses the coils in most modern TVs.

If the fault persists try turning all the equipment off completely and just turning on the TV.

Does it still happen?

If it doesn't it's interference and re-siting equipment is the cure. If it does it could still be interference from the speakers (repositioning will prove this one way or the other - the sub's positioning sounds like a candidate) or is a fault internal to the set itself.

Speakers don't have to be in use to be the cause of the problem; the magnets in the drive units are the culprits when speakers are the cause and they radiate magnetic fields whether they are in use or not. Even shielded drive units typically show some degree of radiation; it's just that they hold it down to what are usually acceptable levels.

Harassed Dad · 29-09-2007, 16:21

Quote:

Does it disappear when the set is switched completely off (not just to standby) and then on again?

Switching off completely degausses the coils in most modern TVs.

If the fault persists try turning all the equipment off completely and just turning on the TV.

Will try that next time it occurs - TV is always swithced off between uses, as is all the other kit, but I haven't yet tried an 'all off' when it occurs then 'on' again immediately afterwards. Effect is an irritant at the moment, but doesn't prevent TV viewing.

Appreciate that I may well just be not follwing the advice so kindly given; I still cannot understand how this fault could be related to the speakers. The colour distortion is always in the same place, and to the same degree, but is intermittent - in evidence some days yet wholly devoid on others. Speakers do not move on a day to day basis but the setup has swapped around in the house moves over the past few years. Sub has been behind, to the side and over 5m away, all with the same intermittent fault. AV kit underneath has changed little but once again, the fault was there when the stack was only a Toshiba DVD, JVC video and Sky box, none of which are located under the TV anymore. Even the stand has changed.

Nigel Goodwin · 29-09-2007, 17:11

If it's intermittent it's either an intermittent external magnetic source (like a vacuum cleaner), a faulty posistor (inside the TV), or a faulty tube.

Also deguassing only takes place when you turn the set ON from stone cold, it's what makes the thudding, humming noise when you turn it on. Turning the set off and back on won't usually deguass.

Etaoin · 29-09-2007, 18:48

Quote:

Originally Posted by Nigel Goodwin

If it's intermittent it's either an intermittent external magnetic source (like a vacuum cleaner), a faulty posistor (inside the TV), or a faulty tube.

Also deguassing only takes place when you turn the set ON from stone cold, it's what makes the thudding, humming noise when you turn it on. Turning the set off and back on won't usually deguass.

Yes - forgot to mention that most sets need to be cold!

Harassed Dad · 29-09-2007, 21:57

I can rule out the intermittent external magnetic source - no consistent other appliance running, or even few appliances, and it can't be location as the fault has occured in 4 different houses.

The degaussing from cold explains why it goes away when left over night. Just as well I don't use the standby function.

Looks like I'll just have to wait for the fault to worsen and persuade my better half to allow an upgrade to a shiny new flat panel TV.

I imagine if it's the tube it puts the TV beyond economical repair; does a faulty posistor do the same?

Nigel Goodwin · 29-09-2007, 22:04

Quote:

Originally Posted by Harassed Dad

I imagine if it's the tube it puts the TV beyond economical repair; does a faulty posistor do the same?

A tube would cost more than the TV did when new, a posistor is cheap - probably £30-£40 for the job?.

Harassed Dad · 30-09-2007, 09:40

Thank you to broadz, Etaoin and Nigel for all the advice.

I'll try to make sure my better half doesn't see how cheap a posistor could be, and use the 'it could be the tube' reason as an excuse for a new flat panel HD TV.

Jason Bourne · 30-09-2007, 12:50

It could be as simple as an on/off switch fault.

I know that a few Sony's had this problem many years ago. As explained in previous posts about degaussing, when you press the on/off switch it degausses the tube, but in certain models of Sony a seperate set of contacts on the switch carried this out, and these were faulty. Hence it only degaussed the tube every now and again.

Nigel Goodwin · 30-09-2007, 13:24

Quote:

Originally Posted by Jason Bourne

It could be as simple as an on/off switch fault.

I know that a few Sony's had this problem many years ago. As explained in previous posts about degaussing, when you press the on/off switch it degausses the tube, but in certain models of Sony a seperate set of contacts on the switch carried this out, and these were faulty. Hence it only degaussed the tube every now and again.

No they don't, I've been repairing Sony TV's (and others) for 36 years, no Sony set has ever had seperate contacts for deguassing on the switch - nor has any other set I've seen or heard of.

Most of the later Sony CRT sets used a timed relay to switch the posistor though - this means that it's only activated for a few seconds after switch on. Then the relay disconnects the posistor, allowing it to cool down - so if the set has been on for a good while the posistor will be cool, and you can switch off and then back on, and still get the deguassing. Normal sets have the posistor permanently powered, so you need to turn it off for 30 minutes or so.

This isn't some clever faster deguassing scheme - it's simply to reduce power consumption - particularly in standby.

Jason Bourne · 30-09-2007, 15:26

Quote:

Originally Posted by Nigel Goodwin

No they don't, I've been repairing Sony TV's (and others) for 36 years, no Sony set has ever had seperate contacts for deguassing on the switch - nor has any other set I've seen or heard of.

Most of the later Sony CRT sets used a timed relay to switch the posistor though - this means that it's only activated for a few seconds after switch on. Then the relay disconnects the posistor, allowing it to cool down - so if the set has been on for a good while the posistor will be cool, and you can switch off and then back on, and still get the deguassing. Normal sets have the posistor permanently powered, so you need to turn it off for 30 minutes or so.

This isn't some clever faster deguassing scheme - it's simply to reduce power consumption - particularly in standby.

I must stand corrected.

Obviously my 6 years working for Sony (Many years ago) means nout!

Nigel Goodwin · 30-09-2007, 21:22

Quote:

Originally Posted by Jason Bourne

I must stand corrected.

Obviously my 6 years working for Sony (Many years ago) means nout!

Depends what you did for them?

28-09-2007, 09:00	#1
Harassed Dad Forum Member Join Date: Jul 2007 Location: Shropshire Posts: 96	Old school TV problem We've got a widescreen JVC 32" CRT that has run well over a number of years, but has an increasingly regular intermittent fault. For some reason, occasionally when you turn the TV on the bottom left hand corner of the screen has a blue glow in a crescent shape radiating from the corner, where the blue is most intense. Doesn't happen all the time, and is more noticeable when watching sport (blue grass in that area). It's happened a few times when not watching sport as well, lastly giving a few of the characters in Corrie a worse skin tone than they normally sport. Any ideas what is going on and is it fixable? Am loathed to change the TV as it works fine most of the time, and we have 2 young boys who haven't yet grown out of the sticky handprints on the screen phase, so a glass screen is a bonus at the moment.

29-09-2007, 14:13	#3
Harassed Dad Forum Member Join Date: Jul 2007 Location: Shropshire Posts: 96	Good thought - think I can discount it though, for the following reasons: 1) Fault is intermittent, and doesn't relate to speaker usage/sound volume. 2) Fault has remained in the same location despite 3 different houses and 2 different speaker systems. 3) The speaker on the right of the screen is a little closer in the current set-up (still over 12" away). 4) Speakers are on stands, and level with the top of the TV screen, not the bottom corner where the colour occurs. Setup is a JVC 32" widescreen CRT TV, on a glass fronted wooden TV stand. In the cabinet, top to bottom are a Sony amp, Sky+ box and Sony HDD/DVD recorder. Speakers are Elac Cinema 1s, with the sub to the rear of the stand. Closest speaker is the centre one, stood on top of the TV. Previous speakers were Technics, with a larger centre speaker that also stood on top of the TV with no problems. TV speakers are switched off (via the JVC menu system) and the surround system is on whenever the TV is on. Last edited by Harassed Dad : 29-09-2007 at 14:16. Reason: Forgot to put in speakers are on stands

28-09-2007, 09:43	#2
broadz Banned User Join Date: Jun 2006 Posts: 2,313	Tints in one corner of the screen are often caused by a magnetic field being given off by something near that particular corner, particularly speakers. Do you have a stereo surround sound system, and has the speaker nearest that corner of the screen been moved closer to the screen?

29-09-2007, 14:32	#4
Etaoin Forum Member Join Date: May 2007 Posts: 33	Does it disappear when the set is switched completely off (not just to standby) and then on again? Switching off completely degausses the coils in most modern TVs. If the fault persists try turning all the equipment off completely and just turning on the TV. Does it still happen? If it doesn't it's interference and re-siting equipment is the cure. If it does it could still be interference from the speakers (repositioning will prove this one way or the other - the sub's positioning sounds like a candidate) or is a fault internal to the set itself. Speakers don't have to be in use to be the cause of the problem; the magnets in the drive units are the culprits when speakers are the cause and they radiate magnetic fields whether they are in use or not. Even shielded drive units typically show some degree of radiation; it's just that they hold it down to what are usually acceptable levels.

29-09-2007, 16:21	#5
Harassed Dad Forum Member Join Date: Jul 2007 Location: Shropshire Posts: 96	Quote: Does it disappear when the set is switched completely off (not just to standby) and then on again? Switching off completely degausses the coils in most modern TVs. If the fault persists try turning all the equipment off completely and just turning on the TV. Will try that next time it occurs - TV is always swithced off between uses, as is all the other kit, but I haven't yet tried an 'all off' when it occurs then 'on' again immediately afterwards. Effect is an irritant at the moment, but doesn't prevent TV viewing. Appreciate that I may well just be not follwing the advice so kindly given; I still cannot understand how this fault could be related to the speakers. The colour distortion is always in the same place, and to the same degree, *but* is intermittent - in evidence some days yet wholly devoid on others. Speakers do not move on a day to day basis *but* the setup has swapped around in the house moves over the past few years. Sub has been behind, to the side and over 5m away, all with the same intermittent fault. AV kit underneath has changed little *but* once again, the fault was there when the stack was only a Toshiba DVD, JVC video and Sky box, none of which are located under the TV anymore. Even the stand has changed.

29-09-2007, 17:11	#6
Nigel Goodwin Forum Member Join Date: Apr 2006 Location: North Derbyshire Posts: 41,789	If it's intermittent it's either an intermittent external magnetic source (like a vacuum cleaner), a faulty posistor (inside the TV), or a faulty tube. Also deguassing only takes place when you turn the set ON from stone cold, it's what makes the thudding, humming noise when you turn it on. Turning the set off and back on won't usually deguass.

29-09-2007, 18:48	#7
Etaoin Forum Member Join Date: May 2007 Posts: 33	Quote: Originally Posted by Nigel Goodwin If it's intermittent it's either an intermittent external magnetic source (like a vacuum cleaner), a faulty posistor (inside the TV), or a faulty tube. Also deguassing only takes place when you turn the set ON from stone cold, it's what makes the thudding, humming noise when you turn it on. Turning the set off and back on won't usually deguass. Yes - forgot to mention that most sets need to be cold!

29-09-2007, 21:57	#8
Harassed Dad Forum Member Join Date: Jul 2007 Location: Shropshire Posts: 96	I can rule out the intermittent external magnetic source - no consistent other appliance running, or even few appliances, and it can't be location as the fault has occured in 4 different houses. The degaussing from cold explains why it goes away when left over night. Just as well I don't use the standby function. Looks like I'll just have to wait for the fault to worsen and persuade my better half to allow an upgrade to a shiny new flat panel TV. I imagine if it's the tube it puts the TV beyond economical repair; does a faulty posistor do the same?

29-09-2007, 22:04	#9
Nigel Goodwin Forum Member Join Date: Apr 2006 Location: North Derbyshire Posts: 41,789	Quote: Originally Posted by Harassed Dad I imagine if it's the tube it puts the TV beyond economical repair; does a faulty posistor do the same? A tube would cost more than the TV did when new, a posistor is cheap - probably £30-£40 for the job?.

30-09-2007, 09:40	#10
Harassed Dad Forum Member Join Date: Jul 2007 Location: Shropshire Posts: 96	Thank you to broadz, Etaoin and Nigel for all the advice. I'll try to make sure my better half doesn't see how cheap a posistor could be, and use the 'it could be the tube' reason as an excuse for a new flat panel HD TV.

30-09-2007, 12:50	#11
Jason Bourne Forum Member Join Date: Aug 2007 Posts: 9	It could be as simple as an on/off switch fault. I know that a few Sony's had this problem many years ago. As explained in previous posts about degaussing, when you press the on/off switch it degausses the tube, but in certain models of Sony a seperate set of contacts on the switch carried this out, and these were faulty. Hence it only degaussed the tube every now and again.

30-09-2007, 13:24	#12
Nigel Goodwin Forum Member Join Date: Apr 2006 Location: North Derbyshire Posts: 41,789	Quote: Originally Posted by Jason Bourne It could be as simple as an on/off switch fault. I know that a few Sony's had this problem many years ago. As explained in previous posts about degaussing, when you press the on/off switch it degausses the tube, but in certain models of Sony a seperate set of contacts on the switch carried this out, and these were faulty. Hence it only degaussed the tube every now and again. No they don't, I've been repairing Sony TV's (and others) for 36 years, no Sony set has ever had seperate contacts for deguassing on the switch - nor has any other set I've seen or heard of. Most of the later Sony CRT sets used a timed relay to switch the posistor though - this means that it's only activated for a few seconds after switch on. Then the relay disconnects the posistor, allowing it to cool down - so if the set has been on for a good while the posistor will be cool, and you can switch off and then back on, and still get the deguassing. Normal sets have the posistor permanently powered, so you need to turn it off for 30 minutes or so. This isn't some clever faster deguassing scheme - it's simply to reduce power consumption - particularly in standby.

30-09-2007, 15:26	#13
Jason Bourne Forum Member Join Date: Aug 2007 Posts: 9	Quote: Originally Posted by Nigel Goodwin No they don't, I've been repairing Sony TV's (and others) for 36 years, no Sony set has ever had seperate contacts for deguassing on the switch - nor has any other set I've seen or heard of. Most of the later Sony CRT sets used a timed relay to switch the posistor though - this means that it's only activated for a few seconds after switch on. Then the relay disconnects the posistor, allowing it to cool down - so if the set has been on for a good while the posistor will be cool, and you can switch off and then back on, and still get the deguassing. Normal sets have the posistor permanently powered, so you need to turn it off for 30 minutes or so. This isn't some clever faster deguassing scheme - it's simply to reduce power consumption - particularly in standby. I must stand corrected. Obviously my 6 years working for Sony (Many years ago) means nout!

30-09-2007, 21:22	#14
Nigel Goodwin Forum Member Join Date: Apr 2006 Location: North Derbyshire Posts: 41,789	Quote: Originally Posted by Jason Bourne I must stand corrected. Obviously my 6 years working for Sony (Many years ago) means nout! Depends what you did for them?

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Old school TV problem