Weirdest problem

[Jan Panteltje]

Um, no they don't what? Generate x-rays? Well, I'd have to disagree with
you on that, Andrew. Jan is right. They can -- if the voltage gets high
enough, which it is kept from doing by a circuit that monitors it and shunts
it to ground if it gets too high. It doesn't generally shut the tv down...
just prevents that voltage from going high enough to cause x-rays. If you
shoot a high energy electron beam (you give it higher energy by increasing
the potential) at a metal target, the metal target will emit x-rays. Basic
x-ray theory. (I was an x-ray machine repairman for the army for a while)
It just takes a higher voltage than is used in an average tv. When you were
a kid, didn't your mother tell you not to sit too close to your tv? That's
because she had heard that a television will emit low end x-rays. Because
back then they didn't build prevention into them. Incidentally, the lower
the energy level of an x-ray the more likely it will be to injure the body.
There were kids who ended up with cancer in their feet at that time, because
they would lay with their feet next to the set and watch hours of tv.

If you can't detect any x-rays now, that's because the circuitry to prevent
them is working properly. Also, you may have been measuring at the front of
the picture tube... but those are made of leaded glass (to stop the x-rays)
so they don't emit much in that direction. The glass of the bell and neck,
however, is not leaded, and also is much thinner. Even with the old sets,
the x-rays were emmited mostly out the back of the set. Now you will often
see a metal shell surrounding the bell of a larger set. That is because the
larger picture tube requires a higher voltage in order to accelerate the
beam properly, and they can emit. So they add the shield to catch any stray
x-rays.

You shouldn't accuse people of not knowing something that you don't know.
It can backfire on you.

You talk nonsense.
Almost of not all TV are 25kV
ALL TV sets have stabilized HV, so 'the ciruit' is the stabilizer.
I have had tests in the studio for the monitors, where xrays were actually
measured, and the level was as close to zero not to worry about it (for kids
too).
The metal around the tube has nothing to do with higher voltages, just
screening (degausing coils are in there).
OP mentions there was an xray detector, that is bull, there is not.
If your mama told you not to sit in front of the TV it was likely because
of the adult content.
As I mentioned in an other post in the old sets there was a PD100 parallel
stabilizer that actually DID emit a bit of xrays (it colored the tubes glass),
it was in a metal case with a safety switch.
Many technicians had it open with the switched bridged to check for things
like arcing etc...
So, how many TV (not roentgen sets) did you servie, and how many did you design?
So we know you DO NOT know what you are talking about.
JP

 

[Jan Panteltje]

Hey shit for brains. Speak for yourself.

So, as usual the poster refers to FUD and insults when he cannot come up
with real data.
At least I designed a TV (actually more then one).
And serviced thousands.
And not only consumer but in a real studio, where they know what a standard
is.
Now ask mama if you can sit if front of the TV, cause Mickey Mouse is coming.
JP

 

[Gregory L. Hansen]

Um, beg to differ with the "charges up again" statement. If you discharged
it and then got zapped, you just didn't do a good job of discharging it...
maybe because of your equipment, or maybe because of your technique. I was
a tv tech for two years, then a monitor repair tech for nine more. I know.

Electrytic capacitors store some energy chemically, like a battery, I've
read. Maybe there's some similar action in a CRT with... I don't know,
it's a lot of glass and metal in there. With the phospher on the screen?

 

[Activ8]

So, as usual

What the **** are you talking about? Don't make it sound like we've
been through this before because this is the *first* time I've had
to slap you for talking shit. You're insult to Andrew riding on the
snip of an insult toward me is enough to convince me finally that
you are an idiot.

the poster refers to FUD

No doubt here.

and insults when he cannot come up
with real data.

I've seen these things called x-ray detect circuits. They shut the
TV down when the detector fails, too. Last one I saw was bad and
cost $30 to replace.

At least I designed a TV (actually more then one).
And serviced thousands.

In what backward country was that?

And not only consumer but in a real studio, where they know what a standard
is.

There's a standard for designing TVs? Cite. Don't give me that IRE,
NTSC, or PAL shit either. Where's the power supply standard?

 

[Jan Panteltje]

No doubt here.


I've seen these things called x-ray detect circuits. They shut the
TV down when the detector fails, too. Last one I saw was bad and
cost $30 to replace.

I entered 'xray detector tv' in google, and after 13 of 31 pages full of links
I still see no diagram or even an reference.
I have had hundreds of service manuals, still some around here, and no such thing ever,
maybe it was snake oil?
I will gladly admit I am wrong (maybe it is the latest thing) if you show me
a link to a diagram of a TV set (commercial) with one in it, atht actually
DETECTS XRAYS.
Even then I think it is just blah blah, as it makes no sense.
The only backward country that comes to mind now is US, whre they vilate
Geneva conference etc.
Not even a country.
As for idiot, look in the mirror, see?
Oh maybe not, why not keep it that way.

 

[Jan Panteltje]

Electrytic capacitors store some energy chemically, like a battery, I've
read. Maybe there's some similar action in a CRT with... I don't know,
it's a lot of glass and metal in there. With the phospher on the screen?

The conductive layer on the inside may have some resistance, so the tube
does not fully discharge in a second or so.
So only parts close to the HV connection are discharged, a while after you
remove the short the voltage will go up there again, from the remote points.
Anyone who actually removed a tube can try that.
So much for the 'know it alls'.
JP

 

[Ken Weitzel]

I entered 'xray detector tv' in google, and after 13 of 31 pages full of links
I still see no diagram or even an reference.
I have had hundreds of service manuals, still some around here, and no such thing ever,
maybe it was snake oil?
I will gladly admit I am wrong (maybe it is the latest thing) if you show me
a link to a diagram of a TV set (commercial) with one in it, atht actually
DETECTS XRAYS.
Even then I think it is just blah blah, as it makes no sense.
The only backward country that comes to mind now is US, whre they vilate
Geneva conference etc.
Not even a country.
As for idiot, look in the mirror, see?
Oh maybe not, why not keep it that way.

Hi...

I'm an old guy, long retired and stroke damaged, but
maybe I can help to bring a little peace... hey, I'm
a Canadian, that's what we do

Jan, it doesn't detect x-rays. No detectors there, none
at all, never were.

What's happened is that the various and sundry experts
have decided among themselves at what level of HV the
set will emit greater than acceptable radiation...

So, the HV is capped at (or slightly below) that
point. If it rises above the set shuts down.

Hope that helps. Now be nice to each other, and
helpful

Take care.

Ken

 

[SIOL]

Hi...

I'm an old guy, long retired and stroke damaged, but
maybe I can help to bring a little peace... hey, I'm
a Canadian, that's what we do

Jan, it doesn't detect x-rays. No detectors there, none
at all, never were.

What's happened is that the various and sundry experts
have decided among themselves at what level of HV the
set will emit greater than acceptable radiation...

So, the HV is capped at (or slightly below) that
point. If it rises above the set shuts down.

Hope that helps. Now be nice to each other, and
helpful

Take care.

Ken

Sounds reasonable. I've had a milion different monitors dissassembled on my
bench and have NEVER seen actual X-ray detector inside.
Not even in service manuals.

It's usually a bit that shuts down the monitor when primary peak HV
transforme current exceeds some level and that is more or less all.

Regarding being bit by a supposedly empty CRT capacitance, IIRC this is a
long known effect and its being caused by charge bleeding by dielectric- in
this case the glass.

Older techs have known about this when woking with large, high voltage oil
capacitors, whiche were notoriously known for this, ableight it canppen
even wth elkos sometimes to a visible degree.
When charged, charge gets slowly into upper layer of dielectric through
small parasitic current, ion migration etc.

When discarged, trapped charge inside boundary layers of dielectric slowly
trickles back to plates and causes voltage regeneration...

 

[Ken Weitzel]

Ken Weitzel wrote:




Sounds reasonable. I've had a milion different monitors dissassembled on my
bench and have NEVER seen actual X-ray detector inside.
Not even in service manuals.

It's usually a bit that shuts down the monitor when primary peak HV
transforme current exceeds some level and that is more or less all.

Regarding being bit by a supposedly empty CRT capacitance, IIRC this is a
long known effect and its being caused by charge bleeding by dielectric- in
this case the glass.

Older techs have known about this when woking with large, high voltage oil
capacitors, whiche were notoriously known for this, ableight it canppen
even wth elkos sometimes to a visible degree.
When charged, charge gets slowly into upper layer of dielectric through
small parasitic current, ion migration etc.

When discarged, trapped charge inside boundary layers of dielectric slowly
trickles back to plates and causes voltage regeneration...

Hi...

YES! I'm one of those old guys...

Perhaps boring to the younger fellows; but in the
old days if a crt was "gone" but had an unbroken
neck for an inch or so behind the bell, we'd have
them re-built. This meant a special trip to the
re-builder, so we'd save up a bunch before taking
them in.

I can guarantee you that they were well shorted
before being set aside. But if it sat for even
weeks and you foolishly picked it up so your
arm was near the 2nd anode, and you were holding
the dag as well, it was very unpleasant!

Just touching on the original briefly, a
good google might be "tv overvoltage shutdown"

Take care.

Ken

 

[Ken Weitzel]

Ken Weitzel wrote:




Sounds reasonable. I've had a milion different monitors dissassembled on my
bench and have NEVER seen actual X-ray detector inside.
Not even in service manuals.

It's usually a bit that shuts down the monitor when primary peak HV
transforme current exceeds some level and that is more or less all.

Regarding being bit by a supposedly empty CRT capacitance, IIRC this is a
long known effect and its being caused by charge bleeding by dielectric- in
this case the glass.

Older techs have known about this when woking with large, high voltage oil
capacitors, whiche were notoriously known for this, ableight it canppen
even wth elkos sometimes to a visible degree.
When charged, charge gets slowly into upper layer of dielectric through
small parasitic current, ion migration etc.

When discarged, trapped charge inside boundary layers of dielectric slowly
trickles back to plates and causes voltage regeneration...

Hi...

YES! I'm one of those old guys...

Perhaps boring to the younger fellows; but in the
old days if a crt was "gone" but had an unbroken
neck for an inch or so behind the bell, we'd have
them re-built. This meant a special trip to the
re-builder, so we'd save up a bunch before taking
them in.

I can guarantee you that they were well shorted
before being set aside. But if it sat for even
weeks and you foolishly picked it up so your
arm was near the 2nd anode, and you were holding
the dag as well, it was very unpleasant!

Just touching on the original briefly, a
good google might be "tv overvoltage shutdown"

Take care.

Ken

 

[Activ8]

Hi...

I'm an old guy, long retired and stroke damaged, but
maybe I can help to bring a little peace... hey, I'm
a Canadian, that's what we do

Jan, it doesn't detect x-rays. No detectors there, none
at all, never were.

What's happened is that the various and sundry experts
have decided among themselves at what level of HV the
set will emit greater than acceptable radiation...

I think that's called safety. It's also called covering your ass. No
sense getting sued.

I think these things were mainly used on sets with higher anode
voltages, but I do recall one on a smaller set - looked like one of
those motel sets, but it was Sony or something (when I think of
motel sets, I think RCA - that was typical at one time)

It's just a potted circuit in line with the HV lead with two wires
coming out to shut down the power supply if the voltage goes too
high.

If I can get to it, I'll pull the back off this 20+ yr old set that
just failed. It's a console and I suspect I can get a pic of one of
those in line x-ray detect deals.

IIRC I've seen the circuits on Sams photofacts and they were indeed
labeled "x-ray detect". You can look at the simple circuit and see
that that's a misnomer, but lack of knowledge of these things is no
excuse for Jan's flaming Andrew or myself.

 

[Rich Grise]

know.

Electrytic capacitors store some energy chemically, like a battery, I've
read. Maybe there's some similar action in a CRT with... I don't know,
it's a lot of glass and metal in there. With the phospher on the screen?

It's stored in the glass itself. Kinda like an electret. The charge
distorts the atoms of the glass, so that even when it's discharged,
there's some residual charge left. Since glass is an insulator, it
takes awhile for this charge to leak out, so it seems to recharge
itself. (i.e., the atoms don't un-distort immediately.)

I always take a clip to ground and a screwdriver, poke the screwdriver
under the cup until I feel it making good contact with the, well, contact,
and leave it there.

Good Luck!
Rich

 

[Andrew VK3BFA]

Confirmed
JP

Sunshine, if you worked in the industry I would believe you, but you
dont so you talk crap (or as its now known, "spin") - your reference
points are 20 years out of date.
Well, I can only go by current industry experience - 3 years before a
big failure is about average - and thats looking at 40+ Tvs a week -
not 3 Philips in 15 years. And you are partially correct given limited
experience - I have a 20yo philips here still with a good CRT that
has needed totally minimal work. Also have a 14" JVC with rotary
tuners from the 70's, all thats ever done is pop a mains fuse and need
a shot of CRC in a noisy volume pot.Modern Philips are crap by
comparison - hopelessly overengineered in a bizarre way, loust
mechanical access, with woeful documentation run from a call centre in
Bangladesh.(or wherever it is....) If one comes down the driveway to
the workshop, I pretend to be out, or tell the customer straight out
it will cost them heaps to diagnose and fix... Sony are heading the
same way - they closed down their local support centre here a few
years ago, you can play musical chairs for days as the call centres
people are hopeless if the fault isnt in the existing knowledge base
and they shuffle you round the world on hold.... Sony are no longer
worth the premium price they charge. And Trinitron tubes "Always"
looked fantastic when new (thats how they sold them), and its basic
psychology 101 that if you pay a lot of money for something it "must"
be good . They do not have long life, emission goes down pretty
fast.... Have a critical look at a 5 year old Sony next to a new $400
Asian cheapy and tell me then if the Sony was worth the money you paid
for it. You wont tho, becasue you will have got used to the poor
picture over a period of years and so not "see" it.

de VK3BFA Andrew

 

[Mjolinor]

Well, I can only go by current industry experience - 3 years before a
big failure is about average - and thats looking at 40+ Tvs a week -
not 3 Philips in 15 years. And you are partially correct given limited
experience - I have a 20yo philips here still with a good CRT that
has needed totally minimal work. Also have a 14" JVC with rotary
tuners from the 70's, all thats ever done is pop a mains fuse and need
a shot of CRC in a noisy volume pot.Modern Philips are crap by
comparison - hopelessly overengineered in a bizarre way, loust
mechanical access, with woeful documentation run from a call centre in
Bangladesh.(or wherever it is....) If one comes down the driveway to
the workshop, I pretend to be out, or tell the customer straight out
it will cost them heaps to diagnose and fix... Sony are heading the
same way - they closed down their local support centre here a few
years ago, you can play musical chairs for days as the call centres
people are hopeless if the fault isnt in the existing knowledge base
and they shuffle you round the world on hold.... Sony are no longer
worth the premium price they charge. And Trinitron tubes "Always"
looked fantastic when new (thats how they sold them), and its basic
psychology 101 that if you pay a lot of money for something it "must"
be good . They do not have long life, emission goes down pretty
fast.... Have a critical look at a 5 year old Sony next to a new $400
Asian cheapy and tell me then if the Sony was worth the money you paid
for it. You wont tho, becasue you will have got used to the poor
picture over a period of years and so not "see" it.

de VK3BFA Andrew

I have to agree with this, the Painter chip fitted by Philips is the worst
goddam invention ever to be introduced to domestic equipment. It's awful to
change and if a new one isn't booted right first power on then you have to
change it again and it's expensive. I guess that about 95% of the faults on
big Philips TVs can be put down to the Painter chip and those faults are
really varied like for example "it comes on OK then after 20 minutes goes
into standby on it's own, if I turn it on again it runs for another 20
minutes", or "it takes 5 minutes to change channels when I press the remote
button". They are mostly ridiculous problems that shouldn't exist on TVs
today, there is no excuse for it.

Samsung technical support is brilliant. They listen to the people ringing
with problems and they make changes to the sets because of it. They fit
rivets to the heavy current tracks which Philips haven't done for years,
good quality PCBs all round. When they first became popular a few (maybe 5)
years ago they had HT transformer problems and they addressed it big style
the transformer never goes faulty now, the whole TV design is dynamic, no
factory released fixes except for the older models, they change the current
design to cure the fault. Picture quality is still a way off a good Philips
but they are improving every day.

It's also sad to note that "the public" in general seem to be prepared to
accept poorer picture quality in general (not talking about home cinema top
of the range here) than they did 15 years ago. A good 1980s set in top
condition will blow most run of the mill new TVs into touch.

 

[Roderick Stewart]

It's stored in the glass itself. Kinda like an electret.

It's not an electret. It's a capacitor. A plain, simple, non-electrolytic
capacitor. Its place in the circuit enables it to be used as the smoothing
capacitor for the EHT supply. The metal coating on the inside of the bowl is
one plate and graphite coating on the outside is the other plate. The glass
of the tube is the dielectric, and a very good one, hence the ability of a
CRT "capacitor" to store charge for some time.

Rod.

 

[Roderick Stewart]

What's happened is that the various and sundry experts
have decided among themselves at what level of HV the
set will emit greater than acceptable radiation...

So, the HV is capped at (or slightly below) that
point. If it rises above the set shuts down.

In other words, it's an overvoltage safety cutout. It limits the
*voltage* by detecting the *voltage*. It doesn't detect X-rays, but
because its original purpose was to prevent the emission of X-rays (in
the days when TV sets included devices that could do this), it is
sometimes loosely spoken of as an X-ray limiter (or detector). Just
another example of how something can be half-understood by the
half-educated, who then jump to the wrong conclusion.

I've seen overvoltage limiters that use a thyristor (or triac) placed
after a fast-acting fuse, with the intention that a fault situation
will cause the thyristor to present a deliberate short-circuit across
the supply and blow the fuse, thus rendering the equipment safe. An
arrangement like this can be called a "crowbar" circuit, or "crowbar
protection", because of the "brute force" nature of the way it works.
It doesn't mean you'll find a crowbar in your TV set (though you may be
tempted to place one there).

Rod.

 

[Leonard Caillouet]

It's also sad to note that "the public" in general seem to be prepared to
accept poorer picture quality in general (not talking about home cinema top
of the range here) than they did 15 years ago. A good 1980s set in top
condition will blow most run of the mill new TVs into touch.

Sorry, but I have to disagree. The typical consumer has never really cared
about quality very much. Also, all this love for products from the 80s and
90s is mostly just nostalgia for the familiar. For half the price today you
can get a set that is better featured, a better pix, and designed much more
smartly than during most of that period. I'd take a current Sony or Zenith,
for two examples, over what they made in the mid 90s without a second
thought. Also, when I hear people lament that they have a set that is 20
years old that is still going strong I have to laugh. That set is almost
always half the size of the ones that they would buy today and was likely
much more expensive in constant dollars. It also likely had a lot softer
pix. Sure, there is a lot of crap on the market, but the market has changed
quite a bit. Overall, the consumer gets a pretty incredible deal.

Leonard

 

[Mjolinor]

Sorry, but I have to disagree. The typical consumer has never really cared
about quality very much. Also, all this love for products from the 80s and
90s is mostly just nostalgia for the familiar. For half the price today you
can get a set that is better featured, a better pix, and designed much more
smartly than during most of that period. I'd take a current Sony or Zenith,
for two examples, over what they made in the mid 90s without a second
thought. Also, when I hear people lament that they have a set that is 20
years old that is still going strong I have to laugh. That set is almost
always half the size of the ones that they would buy today and was likely
much more expensive in constant dollars. It also likely had a lot softer
pix. Sure, there is a lot of crap on the market, but the market has changed
quite a bit. Overall, the consumer gets a pretty incredible deal.

Leonard

Yes the consumer does get a lot better deal, the price is unbelievable,
being an old git I can remember colour TVs being £350 when a weekly wage was
£20, the price of the TV hasn't changed much but the money is worth a lot
less. Your right, the typical consumer never really cared much for the
quality so I was wrong to say people are satisfied with it, what i meant was
that the quality was much better and still is, if you take a 20 year old TV
that has had a good life and is in top condition then the picture quality
will be better than the same sized new one you buy today. I mended a 100Hz
JVC a few weeks ago, dogs bollocks model and in good order. Sitting on the
bench next to a similar Philips basic 15 year old, same picture on both and
the JVC just did not have the bandwidth of the old Philips. This isn't
exceptional it is an easy comparison to make and is across the range of
"mass market" models.

 

[Andrew VK3BFA]

Um, no they don't what? Generate x-rays? Well, I'd have to disagree with
you on that, Andrew. Jan is right. They can -- if the voltage gets high
enough, which it is kept from doing by a circuit that monitors it and shunts
it to ground if it gets too high. It doesn't generally shut the tv down...
just prevents that voltage from going high enough to cause x-rays. If you
shoot a high energy electron beam (you give it higher energy by increasing
the potential) at a metal target, the metal target will emit x-rays. Basic
x-ray theory. (I was an x-ray machine repairman for the army for a while)
It just takes a higher voltage than is used in an average tv. When you were
a kid, didn't your mother tell you not to sit too close to your tv? That's
because she had heard that a television will emit low end x-rays. Because
back then they didn't build prevention into them. Incidentally, the lower
the energy level of an x-ray the more likely it will be to injure the body.
There were kids who ended up with cancer in their feet at that time, because
they would lay with their feet next to the set and watch hours of tv.

If you can't detect any x-rays now, that's because the circuitry to prevent
them is working properly. Also, you may have been measuring at the front of
the picture tube... but those are made of leaded glass (to stop the x-rays)
so they don't emit much in that direction. The glass of the bell and neck,
however, is not leaded, and also is much thinner. Even with the old sets,
the x-rays were emmited mostly out the back of the set. Now you will often
see a metal shell surrounding the bell of a larger set. That is because the
larger picture tube requires a higher voltage in order to accelerate the
beam properly, and they can emit. So they add the shield to catch any stray
x-rays.

You shouldn't accuse people of not knowing something that you don't know.
It can backfire on you.

Are you some sort of a fucking idiot - of course the TV doesnt have an
xray detector, it monitors eht voltage and shuts it down if it exceeds
the potential required to generate X rays. If you want to argue
semantics, go to alt.argument.stupid.idiots who cant read (or
whatever). You might have been a xray tech in the army, I am a TV tech
now, and if you want to grab any TV schematic you can see the area
labelled "xray protection". And Xrays thru the feet - bugger me, thats
a new one. Do aliens speak to you thru your headphones as well?

de VK3BFA Andrew

 

[Roderick Stewart]

There were kids who ended up with cancer in their feet at that time, because
they would lay with their feet next to the set and watch hours of tv.

When I was young (1950s, possibly as late as early 60s) some shoe shops had
fluoroscopes to show you an X-ray view of a child's feet, so you could see how
well the shoes fitted. I must have had my feet in one of these things several
times a year before the age of about 12. Haven't got cancer in my feet, or
anywhere else (yet). Should I worry?

Rod.