Electrical Engineering - Adjusting pots on tube of monitor while switched on

Author

Adjusting pots on tube of monitor while switched on

Andy

2006-05-02, 10:21 am

I am in the UK.

I have been cleaning out the dust from the inside of my monitor and I
just moved a few pots to make sure their tracks are clean and returned
the pots to how they were.

In fact the only pots I can find are three right next to the coil on the
neck of the picture tube and they are marked:

Y-HC: Y and in small letters, HC
Delta V: capital delta symbol then V
YV: Y and in a small letter, V

What do these do?

To be prfectly honest I think I may have not quite returned them to
their original postion but might be 20 or 30 degrees out.

Can I adjust them with the monitor on? Of course I won't be touching
any HT parts but I wonder if they are inherently too close to the HT to
adjust while the monitor is on?

Must I use an insulated trimming tool rather than a meta scredriver?

thrugoodmarshall@hotmail.com

2006-05-02, 10:21 am

Years ago, my Dad, a learned professional and well respected in his
field, told me this story when I was a boy.

One day he was sitting with all the other well respected learned
professionals in the lounge in the building where they worked.

They had just gotten a new and very expensive piece of equipment
installed, and the installer was training them in the procedures for
using their new equipment.

The equipment was a COLOR television. The first one that many of the
people in the room had ever seen.

After the speech, asked the respected learned professionals in the room
if they wanted the absolute best color picture they could get on this
tv. "Well, of course.", somebody replied.

The installer opened a little door in the front of the device and
pointed to a little row of colored knobs he'd just finished adjusting.
See these little knobs here?

In rapt attention, they all stared...yes..

DON'T F*** WITH THEM.

Clive

2006-05-02, 11:21 am

Dave D

2006-05-02, 11:21 am

"Andy" <nomail@nomail.com> wrote in message
news:Xns97B78B138A65274C1H4@127.0.0.1...
>I am in the UK.
>
> I have been cleaning out the dust from the inside of my monitor and I
> just moved a few pots to make sure their tracks are clean and returned
> the pots to how they were.
>

With respect, that was an extremely foolish thing to do. If you don't
understand the inside of mains operated equipment, you shouldn't be inside
it, let alone turning adjustments. If the pots had been dirty but producing
no symptoms, turning them could have caused a fault that wasn't there before
by dragging the dirt under the wiper.

> In fact the only pots I can find are three right next to the coil on the
> neck of the picture tube and they are marked:
>
> Y-HC: Y and in small letters, HC
> Delta V: capital delta symbol then V
> YV: Y and in a small letter, V
>
> What do these do?
>

They are convergence pots. They alter the relationship of the geometries
between the beams. The red, green and blue images which make up the colour
picture on your monitor must overlap as close to perfectly as possible,
otherwise you will see red, green or blue fringes on different parts of the
image. They should only ever be altered by someone who understands how to
set them up- they can be very difficult to get back if you don't know what
you're doing.

If the picture looks OK, you've got away with it.

At least you didn't alter the static convergence rings on the CRT neck- that
really would have caused problems.

Dave

Adrian C

2006-05-02, 11:21 am

Andy wrote:
> I am in the UK.
>
> I have been cleaning out the dust from the inside of my monitor and I
> just moved a few pots to make sure their tracks are clean and returned
> the pots to how they were.
>

Totally unnecessary operation but as you've fiddled now, it can't hurt
to mess around with some insulated tools and some safety knowledge.
Track down the Sci.Electronics.Rapair FAQ site and read.. (or skip the
monitor if the picture is bad, and get a better one from freecycle.org)

Long time ago a friend bought (then) a quite nice secondhand VHS video
recorder (JVC 3V43) with HiFi heads, still frame advance and all the
toys. Plugged it into his television set and noticed the picture tearing
across from the top. So he 'fixed' it. Took the VCR covers off, got some
sand paper, scrubbed the head drum - found 4 black specks wouldn't
shift. So took a screwdriver and neatly chipped them away...

Yes, this idiot computer programmer's TV was to blame (time constant not
set for VCR) but the video head was now completely beyond service - and
cost to replace as much as the whole recorder cost him :-(

--
Adrian C

Martin Underwood

2006-05-02, 12:21 pm

Adrian C wrote in
4bp7ujF12mjdsU1@individual.net:

> Long time ago a friend bought (then) a quite nice secondhand VHS video
> recorder (JVC 3V43) with HiFi heads, still frame advance and all the
> toys. Plugged it into his television set and noticed the picture
> tearing across from the top. So he 'fixed' it. Took the VCR covers
> off, got some sand paper, scrubbed the head drum - found 4 black
> specks wouldn't shift. So took a screwdriver and neatly chipped them
> away...
> Yes, this idiot computer programmer's TV was to blame (time constant
> not set for VCR) but the video head was now completely beyond service
> - and cost to replace as much as the whole recorder cost him :-(

LOL

I'm in two minds as to whether to dismiss this story as apocryphal or to
accept that there really *are* people who would do this!

I once managed to resurrect my old VCR which started producing *very* snowy
pictures after a tape got jammed inside it and must have shed some oxide
onto the heads. However that was with the aid of a cotton-wool ear-bud
soaked in isopropyl alcohol and very gently stroked over the heads - and
only after a head-cleaning cassette had proved to have no effect. The amount
of crud that came off was quite remarkable. After allowing time for the
alcohol to evaporate (I didn't want the tape sticking to the drum!) I
gingerly fired up the VCR and the picture improved over the course of a few
minutes' playing. After a bit longer, the hi-fi sound came back as well.

But to attack a video head with sandpaper and a screwdriver... gulp!

I'm firmly of the school of thought that says "look as much as you like, but
if it's not broken, don't try to 'fix' it". And when EHT is involved, I'd be
very reluctant to open the case of a monitor, even after it's been switched
off for a while - capacitors can store lethal voltages. If I was going to
attempt to tweak the pots, I'd use a long nylon screwdriver and I'd just
tickle each pot in case the setting was very critical. To be "almost right,
but maybe 20 or 30 degrees out" sounds rather vague.

Clive

2006-05-02, 12:21 pm

"Adrian C" <email@here.invalid> wrote in message
news:4bp7ujF12mjdsU1@individual.net...
>
>
> Yes, this idiot computer programmer's TV was to blame (time constant not
> set for VCR) but the video head was now completely beyond service - and
> cost to replace as much as the whole recorder cost him :-(
>

Reminds me of when I walked into a friends room to find him armed with a
carving knife in one hand and the bezel of his computer monitor in the
other.

Turned out he had a computer game with some text which scrolled at the very
bottom on the screen and was partially obscured by the CRT surround which he
intended to carve away. I quickly pointed out the V-height pot at the back
of his monitor but it took hours to rebuild it as to get the bezel off he
had unplugged every cable and HT lead he could see.

I really am surprised we don't see more people electrocuted whilst messing
around in the back of TVs and monitors...

//Clive.

Bruce H

2006-05-02, 12:21 pm

Couldn't this also have been a result of the VCR's back tension being out of
adjustment or was this occuring only with the regular cable signal?

Bruce

"Adrian C" <email@here.invalid> wrote in message
news:4bp7ujF12mjdsU1@individual.net...
> Andy wrote:
>
> Totally unnecessary operation but as you've fiddled now, it can't hurt to
> mess around with some insulated tools and some safety knowledge. Track
> down the Sci.Electronics.Rapair FAQ site and read.. (or skip the monitor
> if the picture is bad, and get a better one from freecycle.org)
>
> Long time ago a friend bought (then) a quite nice secondhand VHS video
> recorder (JVC 3V43) with HiFi heads, still frame advance and all the toys.
> Plugged it into his television set and noticed the picture tearing across
> from the top. So he 'fixed' it. Took the VCR covers off, got some sand
> paper, scrubbed the head drum - found 4 black specks wouldn't shift. So
> took a screwdriver and neatly chipped them away...
>
> Yes, this idiot computer programmer's TV was to blame (time constant not
> set for VCR) but the video head was now completely beyond service - and
> cost to replace as much as the whole recorder cost him :-(
>
> --
> Adrian C

Chris Vowles

2006-05-02, 2:21 pm

Andy wrote:
> I am in the UK.
>
> I have been cleaning out the dust from the inside of my monitor and I
> just moved a few pots to make sure their tracks are clean and returned
> the pots to how they were.
>
> In fact the only pots I can find are three right next to the coil on the
> neck of the picture tube and they are marked:
>
> Y-HC: Y and in small letters, HC
> Delta V: capital delta symbol then V
> YV: Y and in a small letter, V
>
> What do these do?
>
> To be prfectly honest I think I may have not quite returned them to
> their original postion but might be 20 or 30 degrees out.
>
> Can I adjust them with the monitor on? Of course I won't be touching
> any HT parts but I wonder if they are inherently too close to the HT to
> adjust while the monitor is on?
>
> Must I use an insulated trimming tool rather than a meta scredriver?

I hate to admit this but it rang too much of a bell not to reply ....
as a teenager I had a cheap 14" TV where the image was not in the
correct place,
I turned some very similar sounding pots with a non insulated
screwdriver which came with a meccano set !
Everything went fine with the picture changing until I moved around to
have a better look at the screen and the point of the screwdriver
slipped out of the pot and onto a live pin on the board ....
next thing I knew I was sat on the floor on the other side of the room
with a sore arm and a blackened screwdriver

I did get an electrical engineering degree a few years later ......

Dave D

2006-05-02, 2:21 pm

"Martin Underwood" <news@isp.com> wrote in message
news:44576ec5$0$2546$ed2619ec@ptn-nntp-reader02.plus.net...
> I once managed to resurrect my old VCR which started producing *very*
> snowy pictures after a tape got jammed inside it and must have shed some
> oxide onto the heads. However that was with the aid of a cotton-wool
> ear-bud soaked in isopropyl alcohol and very gently stroked over the
> heads - and only after a head-cleaning cassette had proved to have no
> effect.

Cotton buds should not be used on video heads IMO. The fibres can snag and
break off the heads, or become entangled. There's only two things I ever put
near the drum to clean it- chamois swabs and copier paper, both with
isopropyl alcohol. Both clean the heads very well indeed, and even dry
copier paper does a safe job if one doesn't have the proper tools handy.

Dave

Martin Underwood

2006-05-02, 3:21 pm

Chris Vowles wrote in
e383b9$skh$1$8302bc10@news.demon.co.uk:

> Andy wrote:
> I hate to admit this but it rang too much of a bell not to reply ....
> as a teenager I had a cheap 14" TV where the image was not in the
> correct place,
> I turned some very similar sounding pots with a non insulated
> screwdriver which came with a meccano set !
> Everything went fine with the picture changing until I moved around to
> have a better look at the screen and the point of the screwdriver
> slipped out of the pot and onto a live pin on the board ....
> next thing I knew I was sat on the floor on the other side of the room
> with a sore arm and a blackened screwdriver

I assume that this was mains voltage rather than EHT, otherwise you probably
wouldn't be around to tell the tale.

I once made the elementary mistake of doing some work on an old mains-driven
tape-recorder. I'd switched it off at the power-switch on the tape-recorder,
but I'd forgotten to unplug it. All was fine until - you've guessed - my
finger happened to touch the terminals of the switch. Likewise, I was left
with a very sore, tingling arm - and a feeling that I had just lost one of
my nine lives.

> I did get an electrical engineering degree a few years later ......

Same here.

Adrian C

2006-05-02, 3:21 pm

Bruce H wrote:
> Couldn't this also have been a result of the VCR's back tension being out of
> adjustment or was this occuring only with the regular cable signal?

Nope. He got another video recorder and complained of the same problem.
Didn't take us long to figure out what was up - around the mid
eighties it was fairly common knowledge (here in the UK anyway) that one
of the UHF preset channels (normally the last one of 4 or 8) on a TV set
was reserved for VCR use - he'd used another.

--
Adrian C

Adrian C

2006-05-02, 3:21 pm

Martin Underwood wrote:
All was fine until - you've guessed - my
> finger happened to touch the terminals of the switch. Likewise, I was left
> with a very sore, tingling arm - and a feeling that I had just lost one of
> my nine lives.
>
>
> Same here.
>
>

Took apart (to save the bits) the SMPS from an old Sony betamax video
recorder forgetting to discharge some heavy capacitors first. My stray
fingers met some large DC voltage and by instinct / reflex I flung the
module across the room cutting myself badly on a fold in the metal work.

That electronics degree taught me nothing...

--
Adrian C

charles

2006-05-02, 3:21 pm

In article <4bpk4eF12rgtsU1@individual.net>,
Adrian C <email@here.invalid> wrote:
> Bruce H wrote:
[color=darkred]
> Nope. He got another video recorder and complained of the same problem.
> Didn't take us long to figure out what was up - around the mid
> eighties it was fairly common knowledge (here in the UK anyway) that one
> of the UHF preset channels (normally the last one of 4 or 8) on a TV set
> was reserved for VCR use - he'd used another.

The last channel selector altered the time constant in the line sync
locking so that it could cope with unstable vcr signals.

--
From KT24 - in drought-ridden Surrey

Using a RISC OS5 computer

Martin Underwood

2006-05-02, 6:21 pm

charles wrote in
4e20d41d1acharles@charleshope.demon.co.uk:

> In article <4bpk4eF12rgtsU1@individual.net>,
> Adrian C <email@here.invalid> wrote:
>
>
> The last channel selector altered the time constant in the line sync
> locking so that it could cope with unstable vcr signals.

What was the disadvantage of of using the VCR time constant setting for
off-air reception? Presumably there must have been a disadvantage otherwise
all the channel positions would have been permanently set to the VCR time
constant.

I know my TV (bought in 2000) has different settings on its SCART sockets
than on its phono and S-Video aux inputs on the front panel: the phono and
S-video sockets have more problem locking onto the video output from my
laptop which evidently isn't quite 625/50 specification, whereas the SCARTs
are much more tolerant.

Sam Goldwasser

2006-05-02, 6:21 pm

"Martin Underwood" <news@isp.com> writes:

> Chris Vowles wrote in
> e383b9$skh$1$8302bc10@news.demon.co.uk:
>
>
> I assume that this was mains voltage rather than EHT, otherwise you probably
> wouldn't be around to tell the tale.

Actually, this is a misconception that can prove quite lethal. Generally,
the mains voltage - 115 VAC or 230 VAC - can be more dangerous than the
25 kV or whataver.

Touching the HV may throw you across the room due to the charge on the
CRT capacitance, but probably won't kill you except on a really bad day.
Aside from the capacitor, there is too little current to do any harm.

There are AMPs available from the mains voltage.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

Derek ^

2006-05-02, 7:21 pm

On Tue, 2 May 2006 18:17:10 +0100, "Martin Underwood" <news@isp.com>
wrote:
>
>I assume that this was mains voltage rather than EHT, otherwise you probably
>wouldn't be around to tell the tale.

Naah. It's the volts that jolts but the mills that kills.

In a Vacuum tube colour set CA 1969 about the safest thing to get a
shock off was the 25 Kv. Or so they taught us at BBC training school
Evesham. IIRC effectively limited at about 2.5 ma. OTOH.

http://www.r-type.org/exhib/aaa0021.htm

"The normal anode voltage of 160 V is designed to be exceeded by
pulses of up to 8,000 Volts and 1.4 Amps. 8-((

>
>I once made the elementary mistake of doing some work on an old mains-driven
>tape-recorder. I'd switched it off at the power-switch on the tape-recorder,
>but I'd forgotten to unplug it. All was fine until - you've guessed - my
>finger happened to touch the terminals of the switch. Likewise, I was left
>with a very sore, tingling arm - and a feeling that I had just lost one of
>my nine lives.
>
>
>
>Same here.
>

DG

Roderick Stewart

2006-05-02, 7:21 pm

In article <4457c309$0$33910$ed2619ec@ptn-nntp-reader03.plus.net>, Martin
Underwood wrote:
>
> What was the disadvantage of of using the VCR time constant setting for
> off-air reception? Presumably there must have been a disadvantage otherwise
> all the channel positions would have been permanently set to the VCR time
> constant.

Greater susceptibility to noise on received sugnals, which would cause
raggedness of vertical lines due to variations in line timing. There's a
reason for using what was called "flywheel sync". A shorter time constant
effectively made it work with a smaller "flywheel" - OK for clean locally
generated video signals, but not good for off-air material.

Rod.

Roderick Stewart

2006-05-02, 7:21 pm

In article <e383b9$skh$1$8302bc10@news.demon.co.uk>, Chris Vowles wrote:
> Everything went fine with the picture changing until I moved around to
> have a better look at the screen and the point of the screwdriver
> slipped out of the pot and onto a live pin on the board ....
> next thing I knew I was sat on the floor on the other side of the room
> with a sore arm and a blackened screwdriver
>
> I did get an electrical engineering degree a few years later ......

Excellent. First the practical, then the theory. If you survive the first
and are still interested, you're qualified to have a go at the second.
:-)

Rod.

Chris Youlden

2006-05-02, 8:21 pm

Derek ^ wrote:
> On Tue, 2 May 2006 18:17:10 +0100, "Martin Underwood" <news@isp.com>
> wrote:
>
>
>
> Naah. It's the volts that jolts but the mills that kills.
>
> In a Vacuum tube colour set CA 1969 about the safest thing to get a
> shock off was the 25 Kv. Or so they taught us at BBC training school
> Evesham. IIRC effectively limited at about 2.5 ma. OTOH.
>

In the late sixties I worked with a BBC Electronic Services engineer who
regularly used to check whether EHT was present on a faulty monitor by
removing the plug from the tube and sticking his thumb on it.

Chris Y

Dave D

2006-05-02, 8:21 pm

"Martin Underwood" <news@isp.com> wrote in message
news:44579419$0$23177$ed2e19e4@ptn-nntp-reader04.plus.net...

> I assume that this was mains voltage rather than EHT, otherwise you
> probably wouldn't be around to tell the tale.
>

The EHT in a TV (anode voltage) is *far* less of a threat to life than the
mains.

Dave

Michael Kennedy

2006-05-03, 4:21 am

> In the late sixties I worked with a BBC Electronic Services engineer who
> regularly used to check whether EHT was present on a faulty monitor by
> removing the plug from the tube and sticking his thumb on it.

Ouch! That hurts.. I got zapped from the neckboard on my ms pacman cocktail
table while reaching around inside with it on.. That was a mistake that I
don't plan to repeat any time soon.. ;-)

- Mike

Mark Carver

2006-05-03, 4:21 am

Chris Youlden wrote:
> Derek ^ wrote:
>
>
> In the late sixties I worked with a BBC Electronic Services engineer who
> regularly used to check whether EHT was present on a faulty monitor by
> removing the plug from the tube and sticking his thumb on it.

My grandfather's Christmas party piece was to open up the tin box that
housed the EHT rectifier, and with a damp wooden handle screwdriver,
draw an arc from the anode terminal.

--
Mark
Please replace invalid and invalid with gmx and net to reply.

Roderick Stewart

2006-05-03, 5:21 am

In article <4br1qlF12rrq6U1@individual.net>, Mark Carver wrote:
>
> My grandfather's Christmas party piece was to open up the tin box that
> housed the EHT rectifier, and with a damp wooden handle screwdriver,
> draw an arc from the anode terminal.

I remember one of those translucent orange handled screwdrivers would do
quite well too. I've no idea what the resistance of the handle would be, but
I'd trust it to be a bit more consistent than a wooden spoon.

Slightly safer now of course, though not quite so much fun, because voltage
triplers are the usual thing - not such a big spark.

Rod.

Ashley

2006-05-03, 6:21 am

Roderick Stewart wrote:

> In article <4br1qlF12rrq6U1@individual.net>, Mark Carver wrote:
>
> I remember one of those translucent orange handled screwdrivers would
> do quite well too. I've no idea what the resistance of the handle
> would be, but I'd trust it to be a bit more consistent than a wooden
> spoon.
>
> Slightly safer now of course, though not quite so much fun, because
> voltage triplers are the usual thing - not such a big spark.
>
> Rod.

My father had an eht voltmeter that consisted of a calibrated spark
gap. You turned a knob bringing the balls closer together until the
spark jumped the gap. Then you read off the voltage on a scale.

--
Ashley
For Windsor weather see www.snglinks.com/wx/

tony sayer

2006-05-03, 7:21 am

In article <4br1qlF12rrq6U1@individual.net>, Mark Carver
<mark.carver@invalid.invalid> writes
>Chris Youlden wrote:
>
>My grandfather's Christmas party piece was to open up the tin box that
>housed the EHT rectifier, and with a damp wooden handle screwdriver,
>draw an arc from the anode terminal.

We used to do that to test for EHT, firm we worked for in those days was
too bl**dy tight to buy one.

Had the odd belt of many a CRT that wasn't discharged, but by far and
away were aerial isolator plates that had been bypassed and that wasn't
much fun if you we working up on a roof.

Metal ladder, damp soil, live aerial..Nasty!.....
>

--
Tony Sayer

Clive

2006-05-03, 7:21 am

"Ashley" <news@REMOVEsnglinks.com> wrote in message
news:BJWdneZBBtJN78XZnZ2dnUVZ8qadnZ2d@bt.com...
>
>
> My father had an eht voltmeter that consisted of a calibrated spark
> gap. You turned a knob bringing the balls closer together until the
> spark jumped the gap. Then you read off the voltage on a scale.
>

How accurate would this have been ?

Wouldn't humidity / air quality have a measurable an effect on a spark gap ?

//Clive.

Mark Carver

2006-05-03, 7:21 am

Clive wrote:
> "Ashley" <news@REMOVEsnglinks.com> wrote in message
> news:BJWdneZBBtJN78XZnZ2dnUVZ8qadnZ2d@bt.com...
>
> How accurate would this have been ?
>
> Wouldn't humidity / air quality have a measurable an effect on a spark gap ?

Were they not sealed devices ?

Sam Goldwasser

2006-05-03, 11:21 am

Roderick Stewart <rjfs@escapetime.nospam.plus.com> writes:

> In article <4br1qlF12rrq6U1@individual.net>, Mark Carver wrote:
>
> I remember one of those translucent orange handled screwdrivers would do
> quite well too. I've no idea what the resistance of the handle would be, but
> I'd trust it to be a bit more consistent than a wooden spoon.
>
> Slightly safer now of course, though not quite so much fun, because voltage
> triplers are the usual thing - not such a big spark.

The anode terminal of the HV rectifier tube was connected to the flyback
which was 15.7 kHz AC - similar to the output from a small Tesla
coil. So, as long as the screwdriver had some capacitance, the conductivity
of the handle probably didn't matter much.

With modern flybacks, the output is DC filtered by the CRT capacitance,
so the effects are quite different.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

Tzortzakakis Dimitrios

2006-05-03, 12:21 pm

? "Derek ^" <usenet@miniac.demon.co.uk> ?????? ??? ??????
news:stif52du7gkt7s47medturgqnggf5jl1oe@4ax.com...
> On Tue, 2 May 2006 18:17:10 +0100, "Martin Underwood" <news@isp.com>
> wrote:
probably[color=darkred]
>
> Naah. It's the volts that jolts but the mills that kills.
>
> In a Vacuum tube colour set CA 1969 about the safest thing to get a
> shock off was the 25 Kv. Or so they taught us at BBC training school
> Evesham. IIRC effectively limited at about 2.5 ma. OTOH.
>
> http://www.r-type.org/exhib/aaa0021.htm
>
Thanks a lot for sharing this adress, I could dwell for hours on this
website surfing the now sinister tubes.I have in my possesions this sinister
device which can be seen here
http://www.shuttercity.com/ShowGallery.cfm?AcctID=11354
I think it's something like a mechanical inverter, it produced a mediocre AC
voltage from an AA cell.You can see the brass battery holder on the left and
the coil in the middle with the removable core and in the right the holder
for some strange kind of material, probably some pulverized medicine.For my
thesis in Kozani I chose an AM MW transmitter with the 6C4 triode as an
Oscillator and the 807 pseudo-pentode as the amplifier stage.I chose valves
after failing to find trasistors in this frequency range.It was a very
interesting project.It's quite easy to engineer something with valves,
nothing is very critical
160 V is designed to be exceeded by
> pulses of up to 8,000 Volts and 1.4 Amps. 8-((
>
mains-driven[color=darkred]
tape-recorder,[color=darkred]
left[color=darkred]
of[color=darkred]
>
> DG
>

--
Tzortzakakis Dimitrios
major in electrical engineering,freelance electrician
542nd mechanized infantry batallion
dimtzort AT otenet DOT gr

Roderick Stewart

2006-05-03, 10:21 pm

In article <6wvesnckm0.fsf@saul.cis.upenn.edu>, Sam Goldwasser wrote:
>
> The anode terminal of the HV rectifier tube was connected to the flyback
> which was 15.7 kHz AC - similar to the output from a small Tesla
> coil. So, as long as the screwdriver had some capacitance, the conductivity
> of the handle probably didn't matter much.

I was referring to the fact that most modern EHT circuits will only have 8kV
pulses instead of 25kV pulses, because they use a diode/capacitor multiplier and
a lower voltage transformer.

> With modern flybacks, the output is DC filtered by the CRT capacitance,
> so the effects are quite different.

That happens anyway doesn't it? The coatings on the inside and outside of the
bowl of the CRT constitute the EHT smoothing capacitor.

Rod.

Sam Goldwasser

2006-05-04, 10:21 am

Roderick Stewart <rjfs@escapetime.nospam.plus.com> writes:

> In article <6wvesnckm0.fsf@saul.cis.upenn.edu>, Sam Goldwasser wrote:
>
> I was referring to the fact that most modern EHT circuits will only have 8kV
> pulses instead of 25kV pulses, because they use a diode/capacitor multiplier and
> a lower voltage transformer.
>
>
> That happens anyway doesn't it? The coatings on the inside and outside of the
> bowl of the CRT constitute the EHT smoothing capacitor.

What I was trying to say is that in a modern CRT TV or monitor, there is
no place to find the full HV pulses - 5 kV or 25 kV - since the only
output of the flyback goes directly to the CRT anode and its capacitance.

In old once, the flyback output went to the 1B3 (or whatever) anode and
was AC at that point.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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Important: Anything sent to the email address in the message header above is
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Roderick Stewart

2006-05-04, 10:21 pm

In article <6w4q063qv6.fsf@saul.cis.upenn.edu>, Sam Goldwasser wrote:
>
> What I was trying to say is that in a modern CRT TV or monitor, there is
> no place to find the full HV pulses - 5 kV or 25 kV - since the only
> output of the flyback goes directly to the CRT anode and its capacitance.

If you mean the multiplier, then yes, it would incorporate the EHT rectifier which
would otherwise have been a separate diode. The output terminal of the multilplier
unit would be the cathode of the diode, so no AC at that point.

> In old once, the flyback output went to the 1B3 (or whatever) anode and
> was AC at that point.

Yes, a whacking great pulse equal to the full EHT potential onto the anode of a
separate diode. Treat with extreme respect!

Rod.

Andy

2006-05-05, 8:21 pm

On 02 May 2006, Dave D<dave-d@dave-d.com> wrote:

> They are convergence pots. They alter the relationship of the
> geometries between the beams. The red, green and blue images which
> make up the colour picture on your monitor must overlap as close to
> perfectly as possible, otherwise you will see red, green or blue
> fringes on different parts of the image. They should only ever be
> altered by someone who understands how to set them up- they can be
> very difficult to get back if you don't know what you're doing.
>
> If the picture looks OK, you've got away with it.

Phew!

> At least you didn't alter the static convergence rings on the CRT
> neck- that really would have caused problems.

Hmmm. Let me have a look and see if I can move .... :-)

Alex Coleman

2006-05-05, 8:21 pm

On 02 May 2006, Martin Underwood<news@isp.com> wrote:

> I assume that this was mains voltage rather than EHT, otherwise you
> probably wouldn't be around to tell the tale.

i thought that some posts to a very recent thread said that HT was not
actually so very dangerous but would throw you across a room (the main
danger being how you landed).

Sam Goldwasser

2006-05-05, 9:21 pm

Andy <nomail@nomail.com> writes:

> On 02 May 2006, Dave D<dave-d@dave-d.com> wrote:
>
>
> Phew!
>
>
> Hmmm. Let me have a look and see if I can move .... :-)

Everyone loves to diddle with those magnet rings....

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
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Roderick Stewart

2006-05-06, 5:21 am

In article <Xns97BAEED2F2CB471F3M4@127.0.0.1>, Alex Coleman wrote:
>
> i thought that some posts to a very recent thread said that HT was not
> actually so very dangerous but would throw you across a room (the main
> danger being how you landed).

Electricity doesn't "throw you across a room", so if somebody's
description included this statement you know how much you can trust the
rest of it.

If you find yourself somewhere else in the room after an electric shock,
it will have been your own muscles that put you there.

Rod.

Alex Coleman

2006-05-06, 6:21 pm

On 06 May 2006, Roderick Stewart<rjfs@escapetime.nospam.plus.com>
wrote:

> In article <Xns97BAEED2F2CB471F3M4@127.0.0.1>, Alex Coleman wrote:
>
> Electricity doesn't "throw you across a room", so if somebody's
> description included this statement you know how much you can trust
> the rest of it.
>
> If you find yourself somewhere else in the room after an electric
> shock, it will have been your own muscles that put you there.
>

Steady on Roderick! Now that's a wee bit pedantic.
Are you not happy with ellipsis? Otherwise we will have to sort out
things like:

Water does not satisfiy your thirst, it satisfies your body's thirst.

A car does not run on pertrol, a car's engine runs on petrol.

You do not watch television, you watch images on the tube of the
television.

PHEW!
:-0

David Nebenzahl

2006-05-06, 6:21 pm

Alex Coleman spake thus:

> On 06 May 2006, Roderick Stewart<rjfs@escapetime.nospam.plus.com>
> wrote:
>
>
> Steady on Roderick! Now that's a wee bit pedantic.
> Are you not happy with ellipsis? Otherwise we will have to sort out
> things like:
>
> Water does not satisfiy your thirst, it satisfies your body's thirst.
>
> A car does not run on pertrol, a car's engine runs on petrol.
>
> You do not watch television, you watch images on the tube of the
> television.
>
> PHEW!

Thank you for de-pedantifying that.

--
Pierre, mon ami. Jetez encore un Scientologiste
dans le baquet d'acide.

- from a posting in alt.religion.scientology titled
"France recommends dissolving Scientologists"

Sam Goldwasser

2006-05-06, 8:21 pm

Alex Coleman <no@no-email.com> writes:

> On 06 May 2006, Roderick Stewart<rjfs@escapetime.nospam.plus.com>
> wrote:
>
>
> Steady on Roderick! Now that's a wee bit pedantic.
> Are you not happy with ellipsis? Otherwise we will have to sort out
> things like:
>
> Water does not satisfiy your thirst, it satisfies your body's thirst.
>
> A car does not run on pertrol, a car's engine runs on petrol.
>
> You do not watch television, you watch images on the tube of the
> television.

No, the images and sound are usually a waste of time. Watching the
electronics is more educational.

Roderick Stewart

2006-05-06, 8:21 pm

In article <Xns97BBDDFA9BC2E71F3M4@127.0.0.1>, Alex Coleman wrote:
>
> Steady on Roderick! Now that's a wee bit pedantic.
> Are you not happy with ellipsis?

Apologies if I underestimated you, but there are plenty of people who
apparently really believe that an electric shock will "throw you across
the room". I've no idea how they think it does this, and probably
neither have they, but they've heard it somewhere so it must be true
and will tenaciously defend this viewpoint against all attempts to
correct it.

Rod.

Jeff Liebermann

2006-05-06, 11:21 pm

Chris Vowles <NO_SPAM_PLEASE_chris_vowles@hotmail.com_NO_SPAM_PLEASE>
hath wroth:

>Everything went fine with the picture changing until I moved around to
>have a better look at the screen and the point of the screwdriver
>slipped out of the pot and onto a live pin on the board ....
>next thing I knew I was sat on the floor on the other side of the room
>with a sore arm and a blackened screwdriver

Amazing. That was also one of my earlier introductions to electricity
when I was about 13 or 14 years old. I deduced that anything that
powerful was worth understanding.

I kinda miss the good old daze of tube radios and televisions. After
getting zapped a few times, one automatically developes a healthy
respect for high voltage. In the 2way radio business in the 1960's,
it was mostly tube radios. In Smog Angeles, we would kill off about 1
or 2 technicians each year, mostly from high voltage related
accidents. Darwin would be honored as the unworthy and careless
eliminated themselves.

My wakeup call was holding a cast zinc grounded microphone in one
hand, while probing around the high voltage cage with an NE-2 neon
lamp. The last thing I remember was a bright purple flash from the
NE-2 when I hit the plate cap.

I guess the only high voltage challenges left are CRT's, broadcasting,
and power transmission.

>I did get an electrical engineering degree a few years later ......

Yep. I also managed to graduate college without getting killed or
drafted into the army. I even learned a few things along the way.

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Tom Horne

2006-05-07, 12:21 am

Roderick Stewart wrote:
> In article <Xns97BBDDFA9BC2E71F3M4@127.0.0.1>, Alex Coleman wrote:
>
>
>
> Apologies if I underestimated you, but there are plenty of people who
> apparently really believe that an electric shock will "throw you across
> the room". I've no idea how they think it does this, and probably
> neither have they, but they've heard it somewhere so it must be true
> and will tenaciously defend this viewpoint against all attempts to
> correct it.
>
> Rod.
>

I have to explain that one to apprentices all the time. What throws you
across the room is your own muscles. When an electric shock causes all
of them to contract the stronger ones win the argument and their violent
contracting does the rest. If the shock does not kill you your own body
might throw you off a ladder or into a higher energy shock.

Yes I know that many of you new that but for those that didn't...
--
Tom of the sparks and arcs

"This alternating current thing is just a fad. It is much too dangerous
for general use." Thomas Alva Edison

Derek ^

2006-05-07, 8:21 am

On Tue, 02 May 2006 23:15:22 +0100, Roderick Stewart
<rjfs@escapetime.nospam.plus.com> wrote:

>
>Greater susceptibility to noise on received sugnals, which would cause
>raggedness of vertical lines due to variations in line timing. There's a
>reason for using what was called "flywheel sync". A shorter time constant
>effectively made it work with a smaller "flywheel" - OK for clean locally
>generated video signals, but not good for off-air material.
>

I've only just realised reading this that it's *years* since I saw
ignition interference on my TV, there was a time when everything from
an electric razor upwards could flatten the received signal.

DG

Dave D

2006-05-07, 12:21 pm

"Alex Coleman" <no@no-email.com> wrote in message
news:Xns97BAEED2F2CB471F3M4@127.0.0.1...
> On 02 May 2006, Martin Underwood<news@isp.com> wrote:
>
>
>
> i thought that some posts to a very recent thread said that HT was not
> actually so very dangerous but would throw you across a room (the main
> danger being how you landed).

To clarify- Mains areas inside a monitor or TV are potentially lethal
because there is enough current for the full voltage to be presented across
the body, or from hand to earth and it is either low frequency AC or DC from
the mains smoothing caps- very nasty. There is more than enough available
current to kill- IIRC it only takes around 100mA to do the job! Luckily,
unless one is sweaty or wet, there's a good chance the body's internal
resistance will keep the current well below that and make it a nasty,
frightening experience, rather than meaning your family going out to pick a
coffin!

The EHT, or anode voltage, inside a TV monitor is a much higher voltage, but
as the supply is high impedance the available current is very small (a
couple of milliamps or so), so as soon as it is presented across your body
it loads the supply and the voltage dips dramatically. Also, very high
voltages have a habit of preferring to travel across the skin rather than
through your body. The same thing applies to high frequency pulsed DC like
we have in TVs and monitors, so the effect is probably even more pronounced.

AIUI the most lethal voltage range is surprisingly low- 200V to 2000V or
thereabouts if my memory serves.
EHT at high currents (power grid etc) tends to cause a corona around the
victim and massive burns, but it is not unheard of to survive power line
shocks at several KVs!

Dave

Tom MacIntyre

2006-05-07, 1:21 pm

On Sat, 06 May 2006 18:39:21 -0700, Jeff Liebermann
<jeffl@comix.santa-cruz.ca.us> wrote:

>Chris Vowles <NO_SPAM_PLEASE_chris_vowles@hotmail.com_NO_SPAM_PLEASE>
>hath wroth:
>
>
>Amazing. That was also one of my earlier introductions to electricity
>when I was about 13 or 14 years old. I deduced that anything that
>powerful was worth understanding.
>
>I kinda miss the good old daze of tube radios and televisions. After
>getting zapped a few times, one automatically developes a healthy
>respect for high voltage. In the 2way radio business in the 1960's,
>it was mostly tube radios. In Smog Angeles, we would kill off about 1
>or 2 technicians each year, mostly from high voltage related
>accidents. Darwin would be honored as the unworthy and careless
>eliminated themselves.
>
>My wakeup call was holding a cast zinc grounded microphone in one
>hand, while probing around the high voltage cage with an NE-2 neon
>lamp. The last thing I remember was a bright purple flash from the
>NE-2 when I hit the plate cap.
>
>I guess the only high voltage challenges left are CRT's, broadcasting,
>and power transmission.

Don't try a MWO capacitor...apparently the worst hazard in consumer
repair...never tried it.

Tom

>
>
>Yep. I also managed to graduate college without getting killed or
>drafted into the army. I even learned a few things along the way.

Sam Goldwasser

2006-05-07, 2:21 pm

"Dave D" <dave-d@dave-d.com> writes:

> "Alex Coleman" <no@no-email.com> wrote in message
> news:Xns97BAEED2F2CB471F3M4@127.0.0.1...
>
> To clarify- Mains areas inside a monitor or TV are potentially lethal
> because there is enough current for the full voltage to be presented across
> the body, or from hand to earth and it is either low frequency AC or DC from
> the mains smoothing caps- very nasty. There is more than enough available
> current to kill- IIRC it only takes around 100mA to do the job! Luckily,
> unless one is sweaty or wet, there's a good chance the body's internal
> resistance will keep the current well below that and make it a nasty,
> frightening experience, rather than meaning your family going out to pick a
> coffin!
>
> The EHT, or anode voltage, inside a TV monitor is a much higher voltage, but
> as the supply is high impedance the available current is very small (a
> couple of milliamps or so), so as soon as it is presented across your body
> it loads the supply and the voltage dips dramatically. Also, very high
> voltages have a habit of preferring to travel across the skin rather than
> through your body. The same thing applies to high frequency pulsed DC like
> we have in TVs and monitors, so the effect is probably even more pronounced.

High voltages don't in thermselves prefer the surface. It's the high
frequencies of Tesla coils and to some extent TV and monitor horizontal
deflection that do this.

HV DC will take the path of least resistance.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

Jeff Liebermann

2006-05-07, 3:21 pm

"Dave D" <dave-d@dave-d.com> hath wroth:

>AIUI the most lethal voltage range is surprisingly low- 200V to 2000V or
>thereabouts if my memory serves.

Lower. See:
http://en.wikipedia.org/wiki/Electric_shock
"It is believed that human lethality is most common with AC
current at 100-250 volts, as lower voltages can fail to overcome
body resistance while with higher voltages the victim's muscular
contractions are often severe enough to cause them to recoil
(although there will be considerable burn damage). However,
death has occurred from supplies as low as 32 volts."

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Tom MacIntyre

2006-05-07, 3:21 pm

On Sun, 07 May 2006 10:05:45 -0700, Jeff Liebermann
<jeffl@comix.santa-cruz.ca.us> wrote:

>"Dave D" <dave-d@dave-d.com> hath wroth:
>
>
>Lower. See:
> http://en.wikipedia.org/wiki/Electric_shock
> "It is believed that human lethality is most common with AC
> current at 100-250 volts, as lower voltages can fail to overcome
> body resistance while with higher voltages the victim's muscular
> contractions are often severe enough to cause them to recoil
> (although there will be considerable burn damage). However,
> death has occurred from supplies as low as 32 volts."

And, if I remember right, depending upon the person involved,
somewhere in the 50mA-150mA range is where the heart's rhythm gets
disrupted...I may be wrong.

Tom

Jeff Liebermann

2006-05-07, 4:21 pm

Tom MacIntyre <tom__macintyre@hotmail.com> hath wroth:

>On Sun, 07 May 2006 10:05:45 -0700, Jeff Liebermann
><jeffl@comix.santa-cruz.ca.us> wrote:
>
[color=darkred]
>And, if I remember right, depending upon the person involved,
>somewhere in the 50mA-150mA range is where the heart's rhythm gets
>disrupted...I may be wrong.
>Tom

Yep. The point where fibrillation occurs is where you have problems.
Instead of pumping at 50-70 times per minute, the heard sorta vibrates
at a much higher rate. There's not enough time for blood to go in and
out of the various heart valves and chambers, so blood flow
effectively stops. Giving the heart a good blast of the right
frequency pulses gets it back into sync. I don't know the current
range required to induce fibrillation, but it's not very much.

Anyway, my point was that the most dangerous voltage range is common
household AC power.

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann

2006-05-07, 4:21 pm

Sam Goldwasser <sam@saul.cis.upenn.edu> hath wroth:

>High voltages don't in thermselves prefer the surface. It's the high
>frequencies of Tesla coils and to some extent TV and monitor horizontal
>deflection that do this.

Yep, sorta. The common explanation of why you don't get electrocuted
with RF frequencies is because skin effect causes it to flow on the
surface, where there's little chance of heart and muscle damage.
However, there are those that suggest that the reason RF frequencies
have no effect on human muscles is that the frequency response of
those muscles is insufficiently high for RF to have an effect. At
relatively low frequencies (i.e. 50/60Hz), the muscles respond quite
nicely and violently. At much higher frequencies, they just sit
there.

>HV DC will take the path of least resistance.

DC is also bad because it makes the muscles contract, causing one to
be unable to let go of whatever is causing the shock. Many years ago,
I learned that if you wanna use your hand to check for voltage, use
the back of the hand. If you use the fingers or palm side, you could
easily end up grabbing the wire and not being able to let go.

Incidentally, based on atmospheric potential differences, we have
about 200VDC between our head and our toes. So, why don't we get
electrocuted?

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Dave D

2006-05-07, 5:21 pm

"Sam Goldwasser" <sam@saul.cis.upenn.edu> wrote in message
news:6wac9thi4m.fsf@saul.cis.upenn.edu...
> High voltages don't in thermselves prefer the surface.

I stand corrected!

Dave

SpamTrapSeeSig

2006-05-09, 6:21 am

In article <pq5s525t9gd8oo0ssc3b5ljs2ejiok7rad@4ax.com>, Tom MacIntyre
<tom__macintyre@hotmail.com> writes

>Don't try a MWO capacitor...apparently the worst hazard in consumer
>repair...never tried it.

You wouldn't be posting if you had!

Considering the energy stored and the voltage, it would be almost
certainly fatal if it discharged through the body (instead of across
your hand to the chassis). Nowadays many (most?) of them have a high
value (10 M Ohm?) parallel resistor built into the package so that they
self discharge, but not all of them!

I was highly relieved to find that, when ours started misbehaving, it
was a microswitch, and I didn't have to play with the HT side...

Regards,

Simonm.

--
simonm|at|muircom|dot|demon|.|c|oh|dot|u|kay
SIMON MUIR, BRISTOL UK www.ukip.org
EUROPEANS AGAINST THE EU www.members.aol.com/eurofaq
GT250A'76 R80/RT'86 110CSW TD'88 www.kc3ltd.co.uk/profile/eurofollie/

Richard Lamont

2006-05-09, 7:21 am

Tom MacIntyre wrote:

> Don't try a MWO capacitor...apparently the worst hazard in consumer
> repair...never tried it.

What is an MWO capacitor?

--
Richard Lamont http://www.lamont.me.uk/
<richard@lamont.me.uk>
OpenPGP Key ID: 0x5096714C
Fingerprint: F838 740C 76B4 6EC6 9ECC 1C4D A4DE 3322 5096 714C

Tony Quinn

2006-05-09, 7:21 am

In message <446062b4$0$652$5a6aecb4@news.aaisp.net.uk>, Richard Lamont
<richard@lamont.me.uk> writes
>Tom MacIntyre wrote:
>
>
>What is an MWO capacitor?

I assume Microwave Oven .......
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

Jeff Liebermann

2006-05-09, 12:21 pm

Richard Lamont <richard@lamont.me.uk> hath wroth:

>Tom MacIntyre wrote:
>
>
>What is an MWO capacitor?

Multi-Wave Oscillator.
http://www.altered-state.com/index2.htm?/lmwo/lmwo.htm
http://www.altered-states.net/barry...er161/index.htm
http://www.braintuner.com/mwo.htm
http://www.copenlabs.com/copenmwo.htm
Cures cancer. Satisfaction guaranteed if you live to collect your
money back.

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Ashley

2006-05-10, 12:21 am

SpamTrapSeeSig wrote:

> In article <pq5s525t9gd8oo0ssc3b5ljs2ejiok7rad@4ax.com>, Tom
> MacIntyre <tom__macintyre@hotmail.com> writes
>
>
> You wouldn't be posting if you had!
>
> Considering the energy stored and the voltage, it would be almost
> certainly fatal if it discharged through the body (instead of across
> your hand to the chassis). Nowadays many (most?) of them have a high
> value (10 M Ohm?) parallel resistor built into the package so that
> they self discharge, but not all of them!
>
> I was highly relieved to find that, when ours started misbehaving, it
> was a microswitch, and I didn't have to play with the HT side...
>
>
> Regards,
>
> Simonm.

Mine's just packed up and it's the EHT side!

Found the 550mA 5kV fuse blown. Can't find any shorts so it might just
be the fuse. It's about £7 for a new fuse. Quite a lot if it just blows
again!

--
Ashley
For Windsor weather see www.snglinks.com/wx/

Pat Horridge

2006-05-10, 6:21 am

"Ashley" <news@REMOVEsnglinks.com> wrote in message
news:w6ednU5zJvZ0y_zZRVnyig@bt.com...
> SpamTrapSeeSig wrote:
>
>
> Mine's just packed up and it's the EHT side!
>
> Found the 550mA 5kV fuse blown. Can't find any shorts so it might just
> be the fuse. It's about £7 for a new fuse. Quite a lot if it just blows
> again!

>
> --
> Ashley
> For Windsor weather see www.snglinks.com/wx/

You know the answer.
replace the fuse with a solid short.
Power up in the garden on a long mains lead.
If it goes with a big bang then whatever was at fault will be clear to see
and you can thorw it all away.
If it works then replace the short with the new fuse.
Most likely it's either the capacitor or the magnatron which will make it
cheaper to replace then repair.

SpamTrapSeeSig

2006-05-10, 11:21 am

In article <e3s7s6$ms3$1$830fa7a5@news.demon.co.uk>, Pat Horridge
<pat@remove-spam.vet.co.uk> writes

>You know the answer.
>replace the fuse with a solid short.
>Power up in the garden on a long mains lead.
>If it goes with a big bang then whatever was at fault will be clear to see
>and you can thorw it all away.
>If it works then replace the short with the new fuse.
>Most likely it's either the capacitor or the magnatron which will make it
>cheaper to replace then repair.

Won't comment on the technique (!) but I found spares etc. fairly easy
to obtain on the net. True if it's the Magnetron it'll not be worth it,
but the HT caps weren't that bad, neither were the diodes. Mine's a
Panasonic, YMMV.

Regards,

Simonm.

--
simonm|at|muircom|dot|demon|.|c|oh|dot|u|kay
SIMON MUIR, BRISTOL UK www.ukip.org
EUROPEANS AGAINST THE EU www.members.aol.com/eurofaq
GT250A'76 R80/RT'86 110CSW TD'88 www.kc3ltd.co.uk/profile/eurofollie/

Tzortzakakis Dimitrios

2006-05-11, 2:21 pm

? "Tom Horne" <hornetd@mindspring.com> ?????? ??? ??????
news:Ryd7g.4613$Vn.996@newsread4.news.pas.earthlink.net...
> Roderick Stewart wrote:
>
> I have to explain that one to apprentices all the time. What throws you
> across the room is your own muscles. When an electric shock causes all
> of them to contract the stronger ones win the argument and their violent
> contracting does the rest. If the shock does not kill you your own body
> might throw you off a ladder or into a higher energy shock.
>
> Yes I know that many of you new that but for those that didn't...
> --
> Tom of the sparks and arcs
>
> "This alternating current thing is just a fad. It is much too dangerous
> for general use." Thomas Alva Edison
I would add to this that all voltages above 1000 V are considered HT and are
extremely dangerous.That's why the voltage is stepped down for
distribution;120 or 240 voltas are far less a danger than 20 kV.Typically
units generate power from 6.6 kV to 27 kV which is stepped up for
transmission and stepped down for primary distribution and stepped down
again for home or industry use so that noone changing a lamp won't be
exposed to worse than a nasty schock.I would never dare even get near to a
TV that has its back cover removed and is on,29.5 kV is extremely dangerous
and surely a very painful way to die.

--
Tzortzakakis Dimitrios
major in electrical engineering,freelance electrician
542nd mechanized infantry batallion
dimtzort AT otenet DOT gr

Alex Coleman

2006-05-13, 3:21 pm

On 11 May 2006, Tzortzakakis Dimitrios<dimtzort@otenet.gr> wrote:

> ? "Tom Horne" <hornetd@mindspring.com> ?????? ??? ??????
> news:Ryd7g.4613$Vn.996@newsread4.news.pas.earthlink.net...
> I would add to this that all voltages above 1000 V are considered
> HT and are extremely dangerous.That's why the voltage is stepped
> down for distribution;120 or 240 voltas are far less a danger than
> 20 kV.Typically units generate power from 6.6 kV to 27 kV which is
> stepped up for transmission and stepped down for primary
> distribution and stepped down again for home or industry use so
> that noone changing a lamp won't be exposed to worse than a nasty
> schock.I would never dare even get near to a TV that has its back
> cover removed and is on,29.5 kV is extremely dangerous and surely a
> very painful way to die.
>

Now I thought people here were saying that the a shock from the back
of a TV would make you get thrown across a room but that it would
*not* kill you.

What you now say confuses me.

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